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- Создано: 17-11-21
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PCR TUBES
Описание: PCR TUBES The PCR tube is highly optimized to achieve excellent PCR Supplies performance in various thermal cyclers. These innovative and RNase-free PCR tubes are the results of years of research on the best design of PCR tubes, coupled with meticulous craftsmanship to ensure that each product is as perfect as the first product. The results speak for themselves, and we are happy to introduce our ultimate PCR tube to the world. We will explore some of the defining characteristics of these advanced thin-walled PCR tubes. RNase-free PCR tubes with broad thermal cycler compatibility Our RNase free PCR Tubes are compatible with all the most common thermal cyclers on the market. We make sure to optimize their design to ensure PCR performance that is agnostic to the thermal cycler. This means that no matter which brand of thermal cycler you use, their performance is the same. The pipette is one of the most commonly used handheld instruments in a research laboratory and the model of the pipette is chosen based on your needs for performance, ergonomics and quality. But it doesn’t end there - you may have the most advanced pipette on the market but a poor quality tip means that the reproducibility of your results may be at risk. Don’t be caught out; the fact is that quality Pipette Tips are critical to ensuring that the correct volume of liquid is aspirated and dispensed and that your samples are not contaminated in the process. Here are some quick hints to ensure that your pipette tips are a perfect match for your pipette of choice and do not compromise your lab work. The Reagent Bottle is a special container for various liquids and solid reagents in the laboratory. The shape of the reagent bottle is mainly divided into narrow mouth and wide mouth. Since reagent bottles are only used for normal temperature storage reagents, they are usually made of sodium calcium plain glass. In order to ensure a certain strength, the bottle wall is generally thicker. Reagent bottle is divided into narrow mouth or wide mouth, clear or amber,and with stopper or without stopper. Among them, glass stopper, no matter small mouth, wide mouth, should have inside ground sand processing craft. The specifications of HDPE Reagent Bottles are expressed in volume size, small to 30mL, 60mL, ranging from thousands to tens of thousands of ml. b>Precautions for use: (1) when the reagent bottle is not used, you need to slip the paper between the bottle stopper and the bottle mouth to prevent adhesion. As mentioned above, none of the reagent bottles can be used for heating. (2) according to holding the physical and chemical properties of the reagents needed reagent bottles of the general principle is: dress up solid reagent selection jar, holding liquid reagent - choose fine mouth bottle, all see light is easy to break down, or metamorphic reagent to choose a brown bottle, holding low boiling point volatile reagent chooses frosted PP Reagent Bottles, holding an alkaline reagent selection with a rubber plug reagent bottles, and so on. If the reagent has the above multiple physical and chemical indexes, the appropriate reagent bottle can be selected according to the above principles. (3) some special reagents, such as hydrofluoric acid, are not available in any glass reagent bottles and are used in plastic bottles. An Erlenmeyer flask is a widely used type of laboratory flask that features a conical base with a cylindrical neck. They are usually marked on the side (graduated) to indicate the approximate volume of their contents. It is named after the German chemist Emil Erlenmeyer, who created it in 1861. The conical flask is similar to the beaker, but is distinguished by its narrow neck. The neck allows the flask to be stoppered using rubber bungs or cotton wool. The conical shape allows the contents to be swirled or stirred during an experiment (as is required in titration); the narrow neck keeps the contents from spilling. The smaller neck also slows evaporative loss better than a beaker. The flat bottom of the conical flask makes it unlikely to tip over, unlike the Florence flask. Erlenmeyer flasks are used for pH titrations and in microbiology for the preparation of microbial cultures. Plastic Erlenmeyer Flasks used in cell culture are pre-sterilized and feature closures and vented closures to enhance gas exchange during incubation and shaking. If the flask is to be heated in an oil or water bath, a 'C' shaped lead or iron weight may be placed over the outside to keep the flask firmly planted. When heating, it is usually placed on a ring held to a ring stand by means of a ring clamp. The ring keeps it over a Bunsen burner so that it is heated by the flame of the burner. When set up this way, a wire gauze mesh or pad is placed between the ring and the flask to prevent the flames from directly touching the glass. An alternative way to set up the apparatus is to clamp the flask directly to the ring stand by means of holding it with a test tube clamp around the neck of the flask.
Дата Публикации: 17-11-21
Automatic classification of granite tiles through colour and texture features
Описание: Automatic classification of granite tiles through colour and texture features This paper is about the development of an expert system for automatic classification of granite tiles through computer vision. We discuss issues and possible solutions related to image acquisition, robustness against noise factors, extraction of visual features and classification, with particular focus on the last two. In the experiments we compare the performance of different visual features and classifiers over a set of 12 granite classes. The results show that classification based on colour and texture is highly effective and outperforms previous methods based on textural features alone. As for the classifiers, Support Vector Machines show to be superior to the others, provided that the governing parameters are tuned properly. Highlights We discuss the development of an expert system for automatic classification of granite tiles. We propose new approaches to granite classification based on combined colour and texture analysis. We evaluate the performance of different visual descriptors and classifiers. Combination of colour and texture features proves highly effective in discriminating granite appearance. Classification based on SVM support vector classification outperforms the other methods. People have used granite for thousands of years. It is used as a construction material, a dimension stone, an architectural stone, a decorative stone, and it has also been used to manufacture a wide variety of products. Granite is used in buildings, bridges, paving, monuments, and many other exterior projects. Indoors, polished granite slabs and tiles are used in countertops, tile floors, stair treads and many other design elements. Granite is a prestige material, used in projects to produce impressions of elegance and quality. Some interesting and common uses of granite are shown in the photo collection below. The definition of "granite" varies. A geologist might define granite as a coarse-grained, quartz- and feldspar-bearing igneous rock that is made up entirely of crystals. However, in the dimension stone trade, the word "granite" is used for any feldspar-bearing rock with interlocking crystals that are large enough to be seen with the unaided eye. By this classification, rocks such as anorthosite, gneiss, granite, granodiorite, diabase, monzonite, syenite, gabbro and others are all sold under the trade name of "granite." The quality control process in stone industry is a challenging problem to deal with nowadays. Due to the similar visual appearance of different rocks with the same mineralogical content, economical losses can happen in industry if clients cannot recognize properly the rocks delivered as the ones initially purchased. In this paper, we go toward the automation of rock-quality assessment in different image resolutions by proposing the first data-driven technique applied to granite tiles classification. Our approach understands intrinsic patterns in small image patches through the use of Convolutional Neural Networks tailored for this problem. Experiments comparing the proposed approach to texture descriptors in a well-known dataset show the effectiveness of the proposed method and its suitability for applications in some uncontrolled conditions, such as classifying granite slab under different image resolutions. These ceramic and granite tiles from Italian company Cerdomus are unusual, modern and effortlessly beautiful. The ceramic-granite made tiles mimic gorgeous wood flooring. Their unique appearance brings dynamic contrasts into a modern interior design, offering practical, convenient flooring. Wood-like floor tiles are a timeless choice that turns living spaces into luxurious and unique rooms, filled with comfort, warmth and timeless elegance. These modern floor tiles are excellent for creating an original interior design, adding a contemporary touch to home decorating. Suitable for decorating almost all home interiors, from bathrooms, laundry rooms and entryways to kitchens and living rooms. The nature of granite ensures durability and practicality, exceeding over marble or man-made stone. The durable and attractive floor tiles are made of ceramic-granite. Encouraging to experiment and create fresh and sophisticated floor decor. Designed for few stylish collections, ideal for different interior design and home decorating styles. From country home style to classic, contemporary and eco style. Numerous tile colour shades reflect natural wood yellowish to bleached white and brown colours of natural wood. Monochromatic colour schemes make it easy to create a sleek and modern design for your floor decoration. The tiles come in more vibrant colour combinations for something a little different. All collections from Cerdomus are 100% original, blending nature-inspired themes with contemporary home decorating material. Have a browse through our Granite collection. Flooring is an important part that can determine the appearance of your house. Therefore, the selection of material to be used as a floor must be thoroughly considered. In general, ceramics and granite are often used as floor material. Both have strong characteristics, can last a long time, and have several other aspects that can make it difficult for you to choose. If you are that type of person who likes to play with style and color, ceramic tiles are the right choice for you. This is because ceramic tiles have a large selection of colors, motifs, shapes, styles, and finishing. In conclusion, ceramic tiles have a variety of endless variations. Unlike ceramic tiles, granite grey tiles have limited variation. Granite tiles, which were made from natural stones, tend to have irregular patterns with a limited choice of colors and motifs. In addition, granite tiles only have two kinds of finishing. In terms of maintenance, ceramic tiles are easier to care for because they are not easily scratched, and are not easily imprinted if exposed to stains, dirt, or liquid. In other hand, granite tiles are more porous, which can give you a hard time to remove any stains on them. However, granite tiles are one step ahead of ceramic tiles in terms of strength. They are more resistant to impact and friction, which makes them one of the most durable flooring options. In recent years, the manual recognition and classification of natural stones have become a multifaceted challenge due to the similar patterns and visual appearance. Therefore in the current study, a robust and more effective system has been developed for an automatic classification of natural stones i.e. black granite wall tiles using the Convolutional Neural Networks (CNNs). This approach is based on fine-tuning pre-trained networks such as AlexNet and VGGNet. The techniques of data augmentation such as reflection and rotation are incorporated to reduce the probability of overfitting. Efforts have been made to distinguish the performance of training from scratch and fine-tuning pre-trained models. It is observed that the classification, based on CNNs incorporating color and texture both at the same time, is highly reliable, effective and better than the other conventional methods using visual features separately. The research findings also demonstrated that transfer learning based on fine-tuning a network produced better results in accuracy for the classification task of granite tiles. Gorgeous and tough, granite makes a great countertop material. Unfortunately, greatness has its price: Granite slab countertops start at about $100 per sq. ft. But you can have granite countertops for half that cost (or even less) by using granite tile instead of professionally installed granite slabs. Budget-conscious builders and homeowners have done this for decades—and now there are red granite floor tiles designed especially for countertops. This article will show you how to install these special tiles. Since a countertop sits just a couple of feet below eye level, minor mistakes are easy to see. So we’ll show you how to set your tiles flat, even and perfectly aligned. The materials bill for our countertop and backsplash was less than $50 per sq. ft., including everything from screws and backer board to the tiles themselves. The number of inside and outside corners has a big impact on the total cost: Corners cost us about $40 each. Standard bullnose tiles cost $20 and field tiles just $10 each. This is a two-weekend project for a typical kitchen. You’ll spend about half that time tearing out your old countertop and creating a solid base for the tile. A countertop requires a bit more skill and precision than a wall or floor, so we don’t recommend this as a first-time tile project. In addition to standard tile tools, you’ll need to rent a tile saw for a day. You can’t cut the tiles with a manual cutter. Aside from the tile, all the tools and materials you’ll need are at home centers. Tiles are available at tile stores or online (search for “modular granite tile countertop.”) A few weeks before you tear off your old countertops, pull out a pencil and pad and calculate the number and types of tiles needed. Measure, then sketch your countertop on graph paper, including the sink. Label the tiles (bullnose, field, corners) to assess what’s needed where. When you arrive at a final count, you’re almost ready to place your order. Because the tiles are color-matched before shipping, order a few extra to allow for cutting mistakes. Three extra field tiles and two extra bullnose tiles is a safe allowance for a simple job, but for a complex project, you might want extra insurance.
Дата Публикации: 17-11-21
TURN YOUR KID’S ARTWORK INTO A SCRAPBOOK
Описание: TURN YOUR KID’S ARTWORK INTO A SCRAPBOOK The kids have only been in school for two months, but the papers and artwork are piling up. Normally I keep a select pieces of artwork and recycle the rest (after the kids are in bed). This year I’m taking a different approach. Armed with my Straight Talk Samsung Galaxy S6, I’m taking pictures of their artwork and turning it into a kids art scrapbook. What, you don’t have time to make a scrapbook? Don’t worry, this scrapbook is low maintenance and costs less than $10 to make. Even if you’re not crafty, you’ll be surprised by how simple it is to turn your kid’s artwork into a scrapbook. Grab your smartphone and let’s get started! Now grab that stack of artwork you have piled up in the corner. Pull out your favorite pieces (or have your child help) to photograph. Natural lighting is the best, so photograph outside or near a window. I set up a photography station on our patio. I already have foam boards for my food photography, but you can also use posterboard or cardboard. Make sure it’s bigger than your child’s artwork and the board is a solid neutral color. Here I used black foam board. Set the foam board on a chair or something sturdy. Alternately, you can tape it to a wall or window. Take a 3″ piece of masking or washi tape and roll it onto itself. Attach it to the board. You’re essentially creating a reusable sticky surface to attach the artwork to the board. The hobby of scrapbooking is quite popular. People use kids' scratch coding book to tell a story, chronicle the history of their family, and preserve cherished memories. Most scrapbookers are also having fun and relieving stress. If you have thought about giving scrapbooking a whirl but are clueless where to start, this guide will help. Even if you are not the artistic type, you can still make lovely pages when following some simple rules and guidelines. There are many types of glues sold for scrapbooking; decide what kind you prefer. Examples are glue sticks, liquid glue pens, photo tape, foam dots, and more. The glue needs to photo-safe and acid-free. Albums and Sheet Protectors Albums come in a variety of sizes; the standard size that most beginners use is 12 x 12 inch. This size allows you to use many sizes of photos and still have room for other scrapbooking elements. Make sure the page protectors are Mylar, polypropylene, or polyethylene. Any other page protector will damage and fade your pages with time. Cutting Tools You will want large and small straight edge pairs of scissors. Other options include decorative scissors, paper trimmers, and shape cutters. For advanced art stencil book, a digital die-cut machine is useful. Die cuts are cut paper shapes that you can add to your pages. They are premade and sold in packages. Paper You will want a variety of solid colored and patterned paper. Paper comes in 12 x 12-inch sheets or in 8.5 x 11 inches. It's sold in individual sheets or stacks. Buy only acid-free (ph neutral) and lignin free paper. Acid-free paper has been treated so that the acids present in wood pulp papers are removed. Lignin free means that the paper has been processed to remove the acidic part of the wood pulp in paper. Pens Use pens that have pigment ink. It is fade resistant, colorfast, and waterproof. Always practice writing with your pen on a piece of scrap paper first, before writing on your page layout. Photos are the most essential part of your scrapbook page. Make sure that your photos are well lit and in focus for the best results. Punches are tools in various shapes that are used cut out shapes from paper. Rubber stamps add beauty and interest to the magic water coloring drawing book page. Use embossing powders with a heating tool to give the print dimension. Use markers to add color to the stamped images. Stickers are an essential embellishment to scrapbook pages. Craft stores sell sticker packages in thousands of shapes, themes, and designs especially for scrapbooking. Templates are stencils that can help the artistically challenged make perfect shapes and borders. Place the templates on the paper, trace the shapes, cut out, and glue to your layout. If you determine that scrapbooking is a hobby that you want to continue, you will find inspiration galore in scrapbooking magazines, online videos, scrapbook product manufacturers websites, and personal blogs devoted to the craft. Scrapbooking will give you endless hours of fun, stress relief, and an outlet for your creativity. Mementos including cards, photos and other paper materials can now be simply turned into scrapbooks, which are a original and fun method to display your family memories. For kids, scrapbooking is a wonderful way to combine many facets of graphic arts. In this article we will explain how to design a scrapbook for kids, creating projects that will turn crafts into delightful memories! Scrapbooking is amonst the most entertaining and enjoyable ways of keeping memories safe and meaningful to view. By collecting and keeping bits and pieces of memories as one, anybody can create and tell a story. For kids, scrapbooking is a learning experience, educating them the values of resourcefulness, inspiration, patience, and perseverance. Scrapbooking is a fun activity you can work on with your children. It can also be a project they can enjoy with their playmates and friends. Before you get started teaching your kids the beauty of scrapbooking, there are some things you need to consider. The first idea to consider is their interest in the arts. If your child is drawn to the arts and collecting keepsakes to create a new work of art, then she or he will gravitate toward the activity. They have already shown the drive and the creativity needed to create their masterpiece. If your child is not yet drawn to arts and crafts, it doesn't mean they cannot learn about scrapbooking. As a matter of fact, this is the right time to introduce them into this exciting and enjoyable activity. Apart from your child's interest in arts and crafts, another thing you need to consider is the availability of space where your kids can set up their workspace. Because scrapbooking requires a lot of materials, you will need a space big enough for them to spread out and arrange the materials for creating the scrapbook. It is advisable that you provide a space where kids can work on their cartoon colouring book and a place where they can organize their supplies. If you plan to teach your kids scrapbooking, invest in boxes, bins, file folders or other storage systems to keep different items apart from one another. Next, you need to think about the amount of materials your child will need. As you are about to teach them basic scrapbooking, you can use materials from around your home. Here's a basic list of the materials and supplies your children will need: paper or scrapbook paper, pens and colored pencils, photos, tools such as scissors and stickers. Other items can include albums and scrapbooking magazines for ideas. If you work on a scrapbook for kids, you will need to help your children create an overall theme for the scrapbook or just focus on individual pages, such as a birthday page. Here are a few cost saving tips for parents who wish to teach their children scrapbooking, but choose not to purchase costly scrapbooking supplies and materials: 1. Collect old pictures and your youngsters cut out the photos you no longer need. 2. Whenever you go to the photo lab, ask for the double prints and permit your children experiment with the second print. 3. After finishing a specific project, make sure that you put the leftovers and unused scraps in a container so the kids can enjoy it for another scrapbooking session. 4. Look through your office supplies and magazines and let your kids use any items you are no longer involved in. 5. Help your kids form their thoughts and visual themes before gluing down any materials to the scrapbook paper. Be sure to help them decide the correct order for gluing, so that items are displayed correctly. When working on a scrapbook for kids, remember that part of your job will be to provide the organization necessary for kids to select the images and materials they wish to use. Children scrapbooking projects are for kids of any age. Simply use materials that are age-appropriate. A photo from school, treasured pictures and even greeting cards can be transformed into collages that will speak volumes for years to come.
Дата Публикации: 17-11-21
Calculation Inductance of Toroidal Inductor Wound by Rectangular Cross-Sectional Wire
Описание: Calculation Inductance of Toroidal Inductor Wound by Rectangular Cross-Sectional Wire In this article, we present two methods for calculation of the inductance of toroidal core power inductors wound by rectangular cross-sectional wire, considering that the current density is inversely proportional to the circular coil radius. The first method is to simplify the helical toroidal coil into a thick-walled toroidal, and based on Grover’s toroidal inductor formula, the inductance is obtained by calculation the magnetic flux and the calculation method is simple, but the applicability is poor. The second method is to simplify the helical toroidal coil into a collection of self-closing circular coils, the calculation method is complex but has high accuracy, and the mutual inductance between the circular coils is calculated by the filament method based on the adjusted Grover’s mutual inductance of circular coils with inclined axes. We verify the adjusted Grover’s mutual inductance of filamentary circular coils with inclined axes and the mutual inductance between inclined circular coils with a rectangular cross section. Finally, we compared and analyzed the results calculated by the two methods proposed in this article and the results calculated by the finite element method. The various advantages of toroidal inductors, which are cooler, smaller and more EMI-resistant are discussed. With toroidal inductors, there is an advantage to maintaining a single layer of windings due to which the inductor behaves closer to an ideal component of lower levels of parasitic capacitance. Multi-layer toroidal inductors involve both turn-to-turn capacitance and layer-to-layer capacitance and a very significat start/finish gap capacitance since there is no start/finish gap. This increases the total amount of parasitic capacitance by orders of magnitude. This paper presents a micromachined implementation of embedded toroidal solenoids for high-performance on-chip inductors and transformers, which is highly demanded in radio-frequency integrated circuits (RFICs). Microfabricated on CMOS compatible silicon wafers with post-CMOS micromachining techniques, the RF toroidal components can constrain the magnetic flux into a well-defined path and away from other on-chip RF devices, thereby, being in favor of decrease in RF loss, increase in Q-factor and elimination of electromagnetic interference. By using a technical combination of an anisotropic wet etch and an isotropic dry etc., the micromachined toroidal structure can be used for the formation of metal solenoid by copper electroplating. Processed under low temperature (Max 120 °C for photoresist hard-baking), the three mask microfabrication can be compatible with CMOS IC fabrication in a post-process way. The formed toroidal inductors with 4.92 nH and 8.48 nH inductance are tested, and we obtain maximum Q-factors of 25.7 and 17.8 at 3.6 GHz and 3.1 GHz, while the self-resonant frequencies are 17.3 GHz and 7.4 GHz, respectively. On the other hand, two types of toroidal transformers are also formed and tested, resulting in satisfactory RF-performance. Therefore, the novel techniques for close-loop solenoid inductors are promising for high-performance RF ICs. In electrical engineering a toroidal inductor is used to measure or monitor the electric currents of an AC power circuit as a function of the harmonic distortion . A galvanically isolated current measurement is required, such that the advantages of lower losses nd measurement signals processed directly must be attained . The ferrite core toroid inductors produces a reduced current accurately proporonal to the measured current. The toroidal inductor can be also commonly used for feedback control, and other applications .The design method of toroidal inductors have been developed by a non iterative method, which introduce an equation for estimation of the core size required as function of the wanted inductance and the maximum values specified for induction and current . Another method solution consists in modeling inductors along with the equivalent circuits, calculation of the leakage inductance, core material characteristics, and geometrical configuretion for the minimization of volume inductors in order to simplify the design procedure . Nevertheless, the trend for the current monitoring is driven by cost reduction, an increased functionality, and limited weight/space in some applications .This finally results in constantly increasing frequencies, which comes along with and increased bandwidth and poor stability.Based on electric and magnetic properties, like saturation magnetization, and toroidal-core losses, here is proposed the possibility of application of the grain-oriented silicon-iron cores for current monitoring, because these can reduce phase error and improve its accuracy in measurements of AC current at low frequencies (50 - 60 Hz) . A simple method for toroidal-inductor design at minimum losses is suggested to calculate several inductors accepting a broad tolerance of the core material features.In general, the inductor design procedure described in literature makes use of numerous monograms, and the final result is achieved through several iterations. In special, toroidal inductors have been designed by several engineers with tedious methods . For that reason, the lack of deeper understanding of the fundamental electromagnetic laws, it makes many engineers to consider the design of inductive components a difficult task.The purpose here is to explain a design method based on well-known tools by engineers ; presenting in a simple and easy way the relationships that exists between equivalent circuit and transfer function of a toroidal inductor. The proposed work is developed to meet the following objectives:1) To explain the relationship between equivalent circuit and magnetic parameters of a toroidal inductor;2) To develop the method based on normalized parameters;3) To demonstrate the method validation with a current-signal sensor and evaluate the EN-50160-2-2 standard as a function of single harmonic distortion (SHD) in home use loads . The design method for an anti interference toroidal inductor is proposed as an alternative to power-quality evaluation. The method is based on well-known tools by the engineers in which is presented the relationships that exist between equivalent circuit and transfer function of a toroidal inductor. The proposed design method has been explained with normalized functions based on physical parameters of a toroidal inductor. This work presents the main arguments of the suggested methodology and as demonstration of the design method as function of normalized parameters, is developed a current-signal sensor which has been validated in the laboratory by the EN-50160-2-2 standard to evaluate the power quality in home use loads. In this work a method of design based on normalized parameters for a high flux toroidal inductor were proposed. Based on proposed method a current-signal sensor was designed to monitoring of the AC current waveforms.Two normalized functions have been found. One is the magnetizing inductance, Lm(α), another is magnetizing impedance, Zm(α). These parameter leads to obtain in general an optimal design of any toroidal inductor as a function of α parameter.A toroid was built with recycled grain-oriented silicon-iron foils. From the results was observed that the home use loads do not satisfy the EN-50160-2-2 standard which should be corrected in the future. Also, with some suggestions, the proposed method can be expanded to special design of toroidal inductors for other applications. Ferrites are of great interest for power electronics due to their low power losses and they form an essential part of inductors and transformers used in their main applications areas . Therefore, it is necessary to investigate and model the magnetic properties and the nonlinear behavior of ferrites, which exhibit saturation, hysteresis and power losses. These effects and the great variety of core geometries (e.g., E, RM, POT, toroidal) and other parameters, such as the number of turns, make it difficult to obtain a single model that is both simple and precise. Of all the geometries, the toroidal core (Figure 1a) is the most studied in current literature . Nevertheless, despite these publications there are not enough studies that calculate parameters to be used in circuit simulators, such as inductances in all working regions of the ferrite (linear, intermediate and saturation), geometries and number of turns. In this context, our previous publications have focused on 2D Finite Element Analysis procedures for RM and POT ferrite cores . In addition, in the case of the RM core, we have shown an application of our procedures in a commercial circuit simulator . In this paper we focus on the modeling of ferrite inductors with toroidal cores and their nonlinear behavior. We present a specific procedure to compute the inductance of an inductor with a toroidal ferrite core. We present the 2D model (cross-section of the real inductor) and then we study, by numerical simulations and experimental measurements, if this model is suitable for the simulation of ferrite cores in the linear, intermediate and saturation regions. To do so, we compare 3D and 2D results with experimental measurements. The validation is carried out based on convergence and computational cost, spatial distribution of the magnetic fields and flux and inductance curves. At the same time we present preliminary studies of convergence and computational cost in 2D and 3D, showing the reduction of the computational cost and the similarity of the results. The outline of the paper is as follows. In Section 2, we present and describe the specific Finite Element procedure to calculate the inductance. We also describe in detail the measuring procedure we use to validate the procedure and to calculate the input parameters. In Section 3 we provide results obtained in the preliminary study of the convergence and computational cost, and we show the results of the magnetic flux, inductance and magnetic fields. Finally, Section 4 briefly summarizes our main conclusions.
Дата Публикации: 17-11-21
The integrated impact indicator revisited
Описание: The integrated impact indicator revisited We propose the I3* indicator as a non-parametric alternative to the journal impact factor (JIF) and h-index. We apply I3* to more than 10,000 journals. The results can be compared with other journal metrics. I3* is a promising variant within the general scheme of non-parametric I3 indicators introduced previously: I3* provides a single metric which correlates with both impact in terms of citations (c) and output in terms of publications (p). We argue for weighting using four percentile classes: the top-1% and top-10% as excellence indicators; the top-50% and bottom-50% as shock indicators. Like the h-index, which also incorporates both c and p, I3*-values are size-dependent; however, division of I3* by the number of publications (I3*/N) provides a size-independent indicator which correlates strongly with the 2- and 5-year journal impact factors (JIF2 and JIF5). Unlike the h-index, I3* correlates significantly with both the total number of citations and publications. The values of I3* and I3*/N can be statistically tested against the expectation or against one another using chi-squared tests or effect sizes. A template (in Excel) is provided online for relevant tests. Citations create links between publications; but to relate citations to publications as two different things, one needs a model (for example, an equation). The journal impact factor (JIF) indexes only one aspect of this relationship: citation impact. Using the h-index, papers with at least h citations are counted. One can also count papers with h2 or h/2 citations (Egghe 2008). This paper is based on a different and, in our opinion, more informative model: the Integrated Impact Indicator I3. The 2-year JIF was outlined by Garfield and Sher (1963; cf. Garfield 1955; Sher and Garfield 1965) at the time of establishing the Institute for Scientific Information (ISI). JIF2 is defined as the number of citations in the current year (t) to any of a journal’s publications of the two previous years (t???1 and t???2), divided by the number of citable items (substantive articles, reviews, and proceedings) in the same journal in these two previous years. Although not strictly a mathematical average, JIF2 provides a functional approximation of the mean early citation rate per citable item. A JIF2 of 2.5 implies that, on average, the citable items published 1 or 2 years ago were cited two and a half times. Other JIF variants are also available; for example, JIF5 covers a 5-year window.Footnote1 The central problem that led Garfield (1972, 1979) to use the JIF when developing the Science Citation Index, was the selection of journals for inclusion in this database. He argued that citation analysis provides an excellent source of information for evaluating journals. The choice of a 2-year time window was based on experiments with the Genetics Citation Index and the early Science Citation Index (Garfield 2003, at p. 364; Martyn and Gilchrist 1968). However, one possible disadvantage of the short term (2 years) could be that “the journal impact factors enter the picture when an individual’s most recent papers have not yet had time to be cited” (Garfield 2003, p. 365; cf. Archambault and Larivière 2009). Bio-medical fields have a fast-moving research front with a short citation cycle, and JIF2 may be an appropriate measure for such fields but less so for other fields (Price 1970). In the 2007 edition of Journal Citation Reports (reissued for this reason in 2009) a 5-year JIF (JIF5, considering five instead of only two publication years) was added to balance the focus on short-term citations provided by JIF2 (Jacsó 2009; cf. Frandsen and Rousseau 2005).Footnote2 The skew in citation distributions provides another challenge to the evaluation (Seglen 1992, 1997). The mean of a skewed distribution provides less information than the median as a measure of central tendency. To address this problem, McAllister et al. (1983, at p. 207) proposed the use of percentiles or percentile classes as a non-parametric tilt indicators (Narin 1987Footnote3; see later: Bornmann and Mutz 2011; Tijssen et al. 2002). Using this non-parametric approach, and on the basis of a list of criteria provided by Leydesdorff et al. (2011), two of us first developed the Integrated Impact Indicator (I3) based on the integration of the quantile values attributed to each element in a distribution (Leydesdorff and Bornmann 2011). Since I3 is based on integration, the development of I3 presents citation analysts with a construct fundamentally different from a methodology based on averages. An analogy that demonstrates the difference between integration and averaging is given by basic mechanics: the impact of two colliding bodies is determined by their combined mass and velocity, and not by the average of their velocities. So, it can be argued that the gross impact of the journal as an entity is the combined volume and citation of its contents (articles and other items); but not an average. Journals differ both in size (the number of published items) and in the skew and kurtosis of the distribution of citations across items. A useful and informative indicator for the comparison of journal influences should respond to these differences. A citation average cannot reflect the variation in both publications and citations but an indicator based on integration can do so. One route to indexing both performance and impact via a single number has been provided by the h-index (Hirsch 2005) and its variants (e.g., Bornmann et al. 2011a, b; Egghe 2008). However, the h-index has many drawbacks, not least mathematical inconsistency (Marchant 2009; Waltman and Van Eck 2012). Furthermore, Bornmann et al. (2008) showed that the h-index is mainly determined by the number of papers (and not by citation impact). In other words, the impact dimension of a publication set may not be properly measured using the h-index. One aspect that I3 has in common with the h-index is that the focus is no longer on impact as an attribute but on the information production process (Egghe and Rousseau 1990; Ye et al. 2017). This approach could be applied not only to journals but also to other sets of documents with citations such as the research portfolios of departments or universities. In this study, however, we focus on journal indicators. At the time of our previous paper about I3 (Leydesdorff and Bornmann 2011), we were unable to demonstrate the generic value of the non-parametric approach because of limited data access. Recently, however, the complete Web of Science became accessible under license to the Max Planck Society (Germany). This enables us to compare I3-values across the database with other journal shock indicator stickers such as JIF2 and JIF5, total citations (NCit), and numbers of publications (NPub). The choice for journals as units of analysis provides us with a rich and well-studied domain. Our approach based on percentiles can be considered as the development of “second generation indicators” for two reasons. First, we build on the first-generation approach that Garfield (1979, 2003, 2006) developed for the selection of journals. Second, the original objective of journal selection is very different from the purposes of research evaluation to which JIF has erroneously ben applied (e.g., Alberts 2013). The relevant indicators should accordingly be appropriately sophisticated. Data were harvested at the Max Planck Digital Library (MPDL) in-house database of the Max Planck Society during the period October 15–29, 2018. This database contains an analytically enriched copy of the Sciences Citation Index-Expanded (SCI-E), the Social Sciences Citation Index (SSCI), and the Arts and Humanities Citation Index (AHCI). Citation count data can be normalized for the Clarivate Web of Science Subject Categories (WoS Categories) and theoretically could be based on whole-number counting or fractional counting in the case of more than a single co-author. The unit of analysis in this study, however, is the individual paper to which citation counts are attributed irrespective of whether the paper is single- or multi-authored. The (current) citation window in the in-house database was the period to the end of 2017, at the time of the data collection. We collected substantive items (articles and reviews) using the publication year 2014 with a 3-year citation window to the end of 2017. The results were checked against a similar download for the publication year 2009, that is, 5 years earlier. The year 2014 was chosen as the last year with a complete 3-year citation window at the time of this research (October–November, 2018); furthermore, the year 2009 is the first year after the update of WoS to its current version 5. Non-normalized data The in-house database contains many more journals than the Journal Citation Reports (JCR, which form the basis for the computation of JIF). In order to be able to compare between I3*-values and other indicators, we use only the subset of publications in the 11,761 journals contained in the JCR 2014. These journals all have JIFs and other shock indicator for shipping. Of these journals, 11,149 are unique in the SCI-E and SSCI, and the overlap between SSCI and SCI-E is 612 journals. Another 207 journals could not be matched unequivocally on the basis of journal name abbreviations in the in-house database and JCR, so that our sample is 10,942 journals. Note that we are using individual-journal attributes so that the inclusion or exclusion of a specific journal does not affect the values for the other journals under study. Normalized data Citation counts are also field-normalized in the in-house database using the WoS Categories, because citation rates differ between fields. These field-normalized scores are available at individual document level for all publications since 1980. The I3* indicator calculated with field-normalized data will be denoted as I3*F—pragmatically abbreviating I3*F(99-100, 90-10, 50-2, 0-1) in this case. Some journals are assigned to more than a single WoS category: in these instances, the journal items and their citation counts are fractionally attributed. In the case of ties at the thresholds of a top-x% class of papers (see above), the field-normalized indicators have been calculated following Waltman and Schreiber (2013). Thus, the in-house database shows whether a paper belongs to the top-1%, top-10%, or top-50% of papers in the corresponding WoS Categories. Papers at the threshold separating the top from the bottom are fractionally assigned to the top paper set. Statistics Table 2 shows how to calculate I3* based on publication numbers using PLOS One as an example. The publication numbers in the first columns (a and b) are obtained from the in-house database of the Max Planck Society. These are the numbers of papers in the different top-x%-classes. Since the publication numbers in the higher classes are subsets of the numbers in the lower classes, the percentile classes are corrected (by subtraction) to avoid double counting. Previous research has shown that citation data from different types of Web sources can potentially be used for research evaluation. Here we introduce a new combined Integrated Online Impact (IOI) indicator. For a case study, we selected research articles published in the Journal of the American Society for Information Science & Technology (JASIST) and Scientometrics in 2003. We compared the citation counts from Web of Science (WoS) and Scopus with five online sources of citation data including Google Scholar, Google Books, Google Blogs, PowerPoint presentations and course reading lists. The mean and median IOI was nearly twice as high as both WoS and Scopus, confirming that online citations are sufficiently numerous to be useful for the impact assessment of research. We also found significant correlations between conventional and online impact shipping shock indicator, confirming that both assess something similar in scholarly communication. Further analysis showed that the overall percentage for unique Google Scholar citations outside the WoS were 73% and 60% for the articles published in JASIST and Scientometrics, respectively. An important conclusion is that in subject areas where wider types of intellectual impact indicators outside the WoS and Scopus databases are needed for research evaluation, IOI can be used to help monitor research performance.
Дата Публикации: 17-11-21
Refrigerators
Описание: Refrigerators Now here's a cool idea: a metal box that helps your food last longer! Have you ever stopped to think how a refrigerator keeps cool, calm, and collected even in the blistering heat of summer? Food goes bad because bacteria breed inside it. But bacteria grow less quickly at lower temperatures, so the cooler you can keep food, the longer it will last. A food meat refrigerator is a machine that keeps food cool with some very clever science. All the time your refrigerator is humming away, liquids are turning into gases, water is turning into ice, and your food is staying deliciously fresh. Let's take a closer look at how a refrigerator works! What’s your favorite late night snack – that go-to treat that melts away the troubles of the day as you curl up in front of the TV? Perhaps it’s a creamy bowl of Rocky Road or maybe some delicious, spicy Szechuan chicken left over from a recent take-out feast. Refrigerator-finds like these may make you feel bad about indulging in guilty pleasures, but at least you don't have to feel bad about how high your energy bill will be to cure your cravings. That’s because of innovative technology and meaningful energy conservation standards put into place by the Office of Energy Efficiency and Renewable Energy's Building Technologies Program. In recent decades, the Energy Department has led technological innovation that vastly improved the energy efficiency of our refrigerators and freezers (and thousands of other household appliances). As a result, it’s a lot easier on your pocket and on the environment to keep that ice cream at peak frosty perfection. In fact, today’s refrigerators use only about 25 percent of the energy that was required to power models built in 1975. Even while continually improving efficiency to meet standards, refrigerators have increased in size by almost 20 percent, have added energy-using features such as through-the-door ice, and provide more benefits than ever before. Refrigerators today can be customized to fit consumer needs with touch-screen displays, glass doors, or even a beer tap. The dramatic rise in efficiency began in response to the oil and energy crises of the 1970s when refrigerators typically cost about $1,300 when adjusted for inflation, a hefty price to pay for an energy waster. Refrigeration labels and standards have improved efficiency by two percent per year since 1975. Due to research, useful tools, partnerships with utilities and other organizations, and market initiatives that helped enable top open air curtain refrigerator and other appliance standards, the Energy Department has helped avoid the construction of up to 31 1-GW power plants with the energy saved since the first Federal standards in 1987. That’s the same amount of electricity consumed by Spain annually. The Department will soon have strengthened the standards for household refrigerators three times. Each time, manufacturers have responded with new innovations that enabled their products to meet the new requirements and often to exceed them. Refrigerators that performed above and beyond the minimum standards qualified for the ENERGY STAR label, motivated consumers to care about energy usage, and primed the market for continued efficiency improvements. Decades worth of progressive energy-efficiency standards for refrigerators have translated into big savings for consumers. Compared to refrigerators of the 1970s, today's refrigerators save the nation about $20 billion per year in energy costs, or $150 per year for the average American family. The next proposed increase in refrigerator and freezer efficiency -- scheduled to take effect in 2014 -- will save the nation almost four and a half quadrillion BTUs over 30 years. That’s three times more than the total energy currently used by all refrigeration products in U.S. homes annually. It’s also the equivalent amount of energy savings that could be used to power a third of Africa for an entire year The Energy Department is continuing to invest even more in future innovations for energy efficient products. So go ahead and indulge with those late night snacks and frozen treats. Your fridge has you covered. To learn more about Appliance Standards and how they save consumers money go to the Building Technologies Program website. In this position, Roland Risser was responsible for leading all of EERE's applied research, development and demonstration for renewable energy, including geothermal, solar, and wind and water power.In this position, Roland Risser was responsible for leading all of EERE's applied research, development and demonstration for renewable energy, including geothermal, solar, and wind and water power. GREENSBORO, N.C. — The beige-and-brown General Electric top open glass door refrigerator, circa 1982, whirs in a dark corner of Doris and Anthony Vincent’s basement. Mrs. Vincent, a 70-year-old churchgoer and longtime community volunteer, can date its purchase with precision. In her home here, appliances mark milestones. And that nearly 40-year-old model — one of three refrigerators she owns — tells a story of her re-entry into the work force after having a daughter. She spent much of her first paychecks from her job as a counselor at Bennett College on the refrigerator-freezer combo, with the external ice dispenser and other bells and whistles of its era. “I’d been a stay-at-home mother, you know,” she said. When the couple built their 5,000-square-foot home in 1992, the G.E. went to the basement, to make room for a stainless steel upgrade that holds last night’s dinner and the morning’s juice. But the second refrigerator is no afterthought appliance. It occupies pride of place in many American homes — often because, Mr. Vincent said, yesteryear’s fridges were built to last. That didn’t stop the couple, however, from buying a third model for the basement apartment they keep for guests. Around 35 million U.S. households have two refrigerators, and the Vincents are among the six million households that report owning more than two refrigerators, whether full- or dorm-size units, according to the Energy Information Administration, a federal agency that tracks appliance ownership. That number has climbed from 14 percent of all homes in 1978, when the agency first started surveying Americans, to 30 percent in 2015. About 27 percent of today’s urban homes and almost 40 percent of rural ones have at least two refrigerators. Those numbers will likely change again as the pandemic continues and with the average 10-year life span of newer refrigerators. When stand-alone freezers sold out in stores nationwide in the spring of 2020, months of back orders set off a buying spree on refrigerators. In April, Consumer Reports urged those who couldn’t find a freezer to consider a second upright back sliding door refrigerator instead. The second refrigerator can be a homey holdover or the latest model. And, for many, it can be aspirational. It may fulfill a yen for storage space. For others, its contents may function as edible insurance policies during lean years. And there are countless other reasons for a second fridge: frequent entertaining; storing kimchi or other specialties that take time to age; a tendency toward hoarding; or simply the cost of getting rid of a refrigerator. But class and context matter in the world of multiple fridges, or for that matter, freezers. (Statisticians at the Energy Information Administration call those chest or stand-alone appliances “deer freezers” because of their popularity among Midwestern hunters.) Newer models have made owning a second refrigerator easier on the pocketbook. Once, refrigerators routinely used more than 10 percent of a household’s total power, which prompted old-fridge disposal or buybacks around the country during previous blackouts and energy crises, said William McNary, a research statistician for the agency. “Now it’s nowhere near that,” he said. Modern EnergyStar-rated models can cost as little as 10 cents a day to operate. Despite once-valid concerns about a nation of power-sucking surplus refrigerators, Mr. McNary knows they’re not going away — even in his own family. His in-laws keep an avocado-colored refrigerator from the 1970s in their basement. “I go down there, and it’s got three beers and six ginger ales in it,” he said. “My mother-in-law complains every year at Thanksgiving and holidays that our fridge isn’t big enough” to store sides or uneaten turkey. Ms. Reilly remembers an Italian-American friend whose family removed shelves from an extra fridge to hang homemade sausages. Jonathan Ammons, a food writer in Asheville, N.C., contends that refrigerators transmit culture as much as they chill food. “I am a third-generation multiple fridge-freezer kid,” he said. “It is as deep a part of my culinary heritage as candied yams and sugar beets.” He currently owns one refrigerator and one stand freezer, packed this time of year with discounted whole ducks and broth. Mr. Ammons’s parents have three refrigerators, including one that he stocks with prepared meals for his mother, who is ill and bedridden. He traces the family’s desire to have more than one refrigerator to his grandmother’s traditions and preservation practices, common in Appalachia. “Her house in Bakersville had the smokehouse out back and the canning shed,” he said. “And they had smoked meat. When the freezer came, it became an irreplaceable thing, an ingrained thing with my grandmother, that if you have a freezer, you can preserve things. “I see that as an aspect of Appalachian culture: preserving the things you love and prioritizing it — and growing enough of it that you can stay there through the hard times.” While conventional wisdom suggests that the more mouths there are to feed, the more refrigerators, the statistics don’t bear that out. U.S. households with only two occupants lead in two-fridge ownership. People of color also have second refrigerators in disproportionately high rates. Nearly 20 percent of Black Americans have them, as do 22 percent of Latinos and 23 percent of Asian-Americans. One-third of Native American respondents in the Energy Information Administration’s last major survey of residential energy consumption, completed five years ago, reported having more than one stand up back front sliding door refrigerator. That last figure gave Farina King some pause. She’s a citizen of the Navajo Nation and a history professor in Tahlequah, Okla. While her parents, Phillip and JoAnn Smith, have two refrigerators at their home in Utah, they use the second to feed patients, who travel long distances to her father’s medical clinic, as well as friends and missionaries in their church community. Dr. King knows that second refrigerators are rare in the Navajo Nation, which stretches across three states but has only about a dozen full-service grocery stores. Some people, particularly those in urban or semirural areas, may have two fridges, but the dominant reality is quite different. “Many Navajos on the reservation actually do not have access to the space and electricity” for even a first multi-deck display refrigerator, she said.
Дата Публикации: 17-11-21
What is a Filter Press?
Описание: What is a Filter Press? In some batch filtration processes, highly permeable suspensions dewater fast compared to the rest of the process. This work explores the impact of fast-filtering compressible materials on the throughput of fixed-chamber filter presses. The dewatering properties for a compressible yet highly permeable minerals processing slurry are used as inputs to a standard filter press model to explore the effects of operating and design parameters. For fast-filtering materials, maximum throughput is achieved with wide cavities and minimal handling time, while membrane resistance can be significant. Pressure affects the maximum achievable concentration, as given by the strength of the material. Overall, this work demonstrates the combined use of material characterisation and device modelling for filter press optimisation. This article answers three common inquiries. What is a filter press? How does a filter press work? What is a filter press used for? We’ll also give you some advice on sizing your equipment (including your feed pump). Our Sales and Service Team is looking forward to answering any other questions you might have. WHAT IS A FILTER PRESS? A pressure leaf filter is a batch operation, fixed volume machine that separates liquids and solids using pressure filtration. A slurry is pumped into the filter press and dewatered under pressure. It is used for water and wastewater treatment in a variety of different applications ranging from industrial to municipal. M.W. Watermark manufacturers filter presses ranging from .06-600 cubic feet. Slurry is pumped into the filter press. The solids are distributed evenly during the feed (fill) cycle. Solids begin to build on the filter cloth. Most of the solid/liquid separation is done by the filter cake building on the cloths. At first some fines may pass through the cloth (1), but eventually the solids begin to form a layer on the filter cloth (2) much like a pre-coat. That layer traps the fine particles and forms a filter cake (3). As the vertical pressure leaf filter builds pressure, the solids build within the chambers until they are completely full of filter cake. When the chambers are full, the fill cycle is complete. The filtrate (liquid) exits the filter pack (plates) through the corner ports into the manifold; when the correct valves in the manifold are open, the filtrate exits the press through one single point, the filtrate outlet. The Total Cycle time is the Fill Cycle time plus a constant. For presses of 125 cubic feet and under this constant is usually around 45 minutes. This is the time required to close/open the press, perform the Air Blow Down and discharge the filter cake. If the particular application requires operations such as Core Blow or Cake Wash, for example, this constant is longer. HOW LONG DOES A FILL CYCLE TAKE? The Fill Cycle is dependent on many parameters. The most important parameter is the nature of material to be dewatered. A sand slurry releases its water readily and dewaters quickly. On the other hand, an Aluminum Hydroxide waste slurry from beverage can manufacture does not readily release its water and dewaters slowly. The next most important parameter is the concentration of the solids by weight in the slurry. The Fill Cycle for a 5% solids slurry is about twice as long as a 10% solids slurry (with all other parameters being equal). This is because the press has to process half of the water to fill with solids. Other parameters include the thickness of the filter cake, the maximum feed pressure which the slurry is fed to the press, and the filter cloth selection. These parameters are typically fixed during the proposal process. CAN YOU GIVE SOME EXAMPLES OF FILL CYCLES? With 32mm (1.25”) cake chamber thickness, 100 psi max feed to the press and a 3-5 SCFM filter cloth, a 5% sand slurry would be expected to dewater in 20-30 minutes and a 10% sand slurry in 10-15 minutes. Conversely, the 5% Aluminum Hydroxide slurry may take 4-6 hours to dewater, while the 10% slurry would dewater in 2-3 hours. We have an in-house laboratory where we can test a sample of your slurry to determine the Fill Cycle time as well as the other outputs from pressure filtration testing. Give us a call. WILL A SMALL PRESS FILL FASTER THAN A LARGER PRESS? The Fill Cycle times for a 1 cubic foot, 10 cubic foot and 100 cubic foot press are approximately the same. Press volume is the ability to remove solids. Associated with this volume is the square feet of surface area in the press. Square footage is the ability to process fluid. As volume is added, square feet of surface area is proportionally added and the cubic foot to square foot ratio remains (roughly) constant. Therefore, the Fill Cycle Time is basically the same. Example A 1 cubic foot press at 32mm cake thickness has 22 square feet of surface area for a 0.045 cf/sf ratio. A 10 cubic foot press at 32mm cake has 211 square feet of surface area for a 0.047 cf/sf ratio. WHAT TYPE OF PUMP SHOULD I USE TO FEED MY PRESS? For press capacities of 125 cubic feet or less, the double Air Operated Diaphragm pump (AOD) is uniquely suited for vibrating filter operations. The filter press is not a constant flow device. As the solids build up within the press, the resistance to flow increases and the flow rate through the press decreases. At a given air pressure supply, the time between pump strokes for an AOD pump, then, constantly increases with no harm done to the pump. On presses larger than 125 cubic feet in capacity, AOD pumps become impractical because three or more large (3”) pumps would be required. On large presses pumps such as progressive cavity, centrifugal and piston membrane pumps are often used. Control of these constant flow pumps is through a PLC that requires input from a pressure transducer and a flow meter to control a VFD (Variable Frequency Drive) on the pump motor. For a small press the control system for a constant flow pump is generally more costly than the press itself. SO, ARE THERE ANY RULES OF THUMB ON PRESS FEED FLOW RATES THAT CAN BE USED TO SELECT A PUMP SIZE? For presses 125 cubic feet and less, an AOD pump that can deliver 0.1 gallons per minute per square foot of surface area after the initial fill should be selected. 800mm, 20 cubic foot press has about 420 square feet of surface area. A pump that can deliver 42 gpm should be selected. This can be either a 1.5” or 2” AOD pump. A 1200mm, 100 cubic foot press has 2030 square feet of surface area. While one 3” AOD pump can deliver 203 gpm, the operating envelope would be on the edge of the curves. Here, two 3” AOD pumps in parallel would be recommended. For the very large presses a constant flow pump would be sized to be able to fill the void of the press in about 4-6 minutes. For example, a 300 cubic foot press is about 2,250 gallons. To initially fill this press in 5 minutes requires a pump that can deliver 450 gpm. IS THERE ANY WAY TO QUICKLY RELATE THIS RULE OF THUMB INFORMATION TO PRESS CAPACITY? The vast majority of filter presses sold are 125 cubic feet in capacity and below. The table below gives quick guidelines. However, there are always overlaps at the ends of the range. A 15 (or 16) cubic foot press can be fed with a 1.5” or 2” pump. For feed pumping purposes, the fully automatic filter press can be viewed as an open system. There can always be one more stroke of the AOD pump. It may take days to get it, but there will be one more stroke. A practical end of the dewatering cycle has to be determined. For all practical purposes, the Fill Cycle is finished when the flow rate through the press at terminal pressure is 0.01 gpm per square foot of surface area. For an 800mm, 20 cf press with 420 square feet of surface area, this is 4.2 gpm. There is a correlation between this terminal flow rate and the time between pump strokes at terminal feed pressure, typically 100 psi. Depending on the nature of the slurry being dewatered, the interval between pump strokes at terminal pressure is 30-60 seconds. DO I GIVE THE FEED PUMP 100 PSI OF AIR PRESSURE FROM THE START AND STAND THERE TIMING THE INTERVAL BETWEEN PUMP STROKES OR IS THERE SOME WAY TO AUTOMATE THIS? The press Fill Cycle can be started at full blast by giving the AOD pump a 100 psi air supply, walking away and coming back in a couple of hours to check on the interval between pump strokes. However, to save on wear and tear on the AOD feed pump and prolong the useful life of the filter cloths, it would be preferable to ramp up the feed pressure to the press. The feed pressure can be manually ramped up by installing a pressure regulator in the air supply line to the AOD pump and ramping up in 25 psi increments for example. The ramp point for the 25, 50 and 75 psi stages would be when there is a 5-10 second interval between pump strokes. On the 100 psi stage the termination point is 30-60 seconds between pump strokes. This ramp up and termination can be done automatically with the M.W. Watermark Automatic Feed Pump Control System (AFPCS). A filter press is one of the oldest and most trusted pieces of dewatering equipment. It’s used for wastewater treatment across a variety of industries and applications. A filter press works by separating out solids from liquids, removing impurities, and suspended solids from industrial wastewater. This allows plant managers to easily handle and dispose of waste while returning clean water to their systems. Filter presses separate liquids and solids. Specifically, the filter press separates the liquids and solids using pressure filtration across a filter media. Afterward, the slurry is pumped into the filter press and then dewaters under pressure. What are the Four Main Components of a Filter Press? Manifold (piping and valves) Filter Cloth (This is key for optimizing filter press operations. Basically, the filter press design is based on the dewatering volume and type of slurry. ChemREADY is an expert in liquid and solid separation and offers a wide range of filter press types and capacities to suit specific application needs for trouble-free, economical dewatering. The origin of the filter press dates to around the mid-19th century in the United Kingdom, where a rudimentary form of the press was used to obtain vegetable oil from seeds. However, it wasn’t until major developments in the mid-20th century that engineers were able to develop the world’s first automatic horizontal-type filter press. It’s this long history of advancements that’s allowed the filter presses of today to achieve significantly lower energy and maintenance costs compared to their belt press and centrifuge counterparts. In fact, the total operating filtration cost for a filter press can easily be 1/6 the cost of what it would be for a belt press or centrifuge. While there are many different styles of modern edible oil filter press, the plate and frame filter press are one of the oldest and most tested types of dewatering equipment available. You can read more on this type of filter press, along with a more detailed comparison between different types of dewatering equipment, in our Water Facts blog on How Industrial Wastewater Pretreatment Works. Filter presses are especially useful as the leftover solids are cheaper and easier to move than the entire slurry. With the clean water that filter presses return, plant managers can discharge that to their local municipalities, watersheds or use the water in their own closed-loop systems, creating highly efficient processes. Common filter press applications include: Mining operations and aggregate Food & beverage production Marble and stone cutting Without a filter press or similar pieces of dewatering equipment, a settling pond is often the first option for water treatment. Not only do ponds require a large amount of real estate to use, but they also lose their ability to clean water over time as the solids that you remove build up in the pond water. This gives ponds an unfavorable long-term ROI as dirty water will eventually start coming back into your process unless you dredge the pond or make a new pond. At ChemREADY, we advise the use of a filter press and other dewatering equipment over a pond in most applications. How does a Filter Press Work? During the fill cycle, the slurry pumps into the filter press and distributes evenly during the fill cycle. Solids build up on the filter cloth, forming the filter cake in the void volume of the plate. The filtrate, or clean water, exits the filter plates through the ports and discharges clean water out the side of the plates. Filter presses are a pressure filtration method. As the filter press feed pump builds pressure, the solids build within the chambers until they are completely full of solids. This forms the cake. The filter cakes release when the plates are full, and the cycle is complete. Also, many higher capacity filter presses use fast action automatic plate shifters which speeding cycle time. Matec specifically designs their filter presses for fully automatic, 24-hour operation in a harsh environment such as mines or chemical manufacturing plants for wastewater treatment. What Is A Filter Press Used For? While the various styles of filter presses work differently, they all operate under similar principles. Slurries of water mixed with solids are pumped into the press by using a feeding pump. Once inside the press, pressure – often from a centrifugal pump or similar device – pushes the slurry through chambers made of filter plates. This removes impurities from the water as “filter cakes” of solids build up on the machine’s filters. Once the chambers of a filter press are full, its filtration cycle is complete, and the machine releases the filter cakes. These cakes are easily removed, allowing you to filter your water at high efficiencies. In filter presses, fast action automatic plate shifters may be used to help speed up cake removal and cycle time. In harsher environments where continuous operation is required – like in mining processes or chemical manufacturing plants – a fully automatic filter press design is needed to handle the 24-hour workloads. To get the best performance out of your filter press, the cloth of the filter should be specifically designed for your application and the types of solids that you are filtering. The following can also be customized to fit your individual needs: Machine design Filtration capacity In addition to these, you can use additional systems such as cloth washing systems, drip trays, and cake shields to further increase filter press performance and functionality. Ultimately, each filter press should be designed based on the expected volume and type of slurry that it will be handling. Since filter presses work using pressure, equipment that increase pressure through the means of high-pressure technology are great for optimizing your filter press system. That’s the secret to success for Matec? filter presses, which use pressures of 21 to 30 bar to handle even the most difficult and hard to treat slurries, no matter the sector or application. Filter presses can be built in a wide range of sizes, from small, lab-scale presses, to those with much larger capacities, such as those with 2000×2000 mm plates.
Дата Публикации: 17-11-21
60 years of integrated circuits
Описание: 60 years of integrated circuits An integrated circuit is a semiconductor wafer on which thousands or millions of tiny resistors, capacitors, and transistors are fabricated. Sometimes called a chip or microchip. The invention of the integrated circuit made technologies of the Information Age feasible. ICs are now used extensively in all walks of life, from cars to toasters to amusement park rides. Integrated circuits (ICs) are self-contained circuits with many separate components such as transistors, diodes, resistors and capacitors etched into a tiny silicon chip. Related Journals of Integrated circuit Journal of Physical Chemistry & Biophysics, Journal of Electrical & Electronic Systems, Analog Integrated Circuits and Signal Processing, IEEE Radio Frequency Integrated Circuits Symposium, IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, Journal of Integrated Circuits and Systems, Proceedings of the Custom Integrated Circuits Conference. On 12 September 1958, Jack Kilby of Texas Instruments demonstrated a working integrated circuit1. The circuit was a phase-shift oscillator that used transistor, resistor and capacitor elements built from a single piece of germanium; the elements were connected into a circuit with the help of thin gold wires. A few months later, Robert Noyce, working at Fairchild Semiconductor, proposed a monolithic integrated circuit2. This planar design was based on silicon and used lines of aluminium, deposited on the insulating silicon dioxide layer that can form on the surface of silicon wafers, to connect the different circuit elements in the single chip. By 1960, a team of engineers at Fairchild Semiconductor had turned this design into a reality. Electronic components, which had previously been discrete units connected with individual wires, could now be integrated into the same piece of semiconducting material. In the 60 years since Kilby’s initial demonstration, progress in STM8S207C8T6 has been astounding. Noyce would go on to co-found Intel, and just how far the company — and the design of integrated circuits — has come in that time is highlighted in this issue of Nature Electronics. In a News & Views article, Suman Datta of the University of Notre Dame reports on Intel’s 10-nanometre logic technology. With this latest design iteration3, the company has introduced a number of unconventional approaches to improve transistor density and performance, including a technique to reduce the spacing between cells and a method to add gate contacts directly over the active area. As a result, they can deliver around 100 million transistors per square millimetre — a transistor density that is 2.7 times higher than that of their previous 14-nm technology, which was introduced in 2014. At this level of complexity, developments are far from straightforward. Earlier this year, it emerged that Intel have encountered problems in the manufacturing of the 10-nm chips, leading to delays in mass production4; the chips are now expected to ship in volume in 2019. And in the past few weeks, GlobalFoundries announced5 that they would stop development of their 7-nm chips (thought to be comparable to Intel’s 10-nm technology). The continued scaling of silicon complementary metal–oxide–semiconductor (CMOS) technology beyond these levels is also likely to prove increasingly difficult. But, at the same time, the applications of computers are evolving, and demand the processing of ever larger amounts of data. As a result, the search for strategies and materials beyond silicon, which could help create the next generation of devices and integrated circuits, remains vital. Carbon nanotubes are among the contenders fighting for a place in the future of electronics, and in our Reverse Engineering column in this issue, Cees Dekker recounts how the first carbon nanotube transistor was built back in 1998. A related contender in this fight is two-dimensional materials, as well as the vertical stacks of different two-dimensional materials known as van der Waals heterostructures. These materials have been used to build a range of promising devices and some basic circuits — even a microprocessor6. The unique challenges involved in trying to build practical integrated circuits from two-dimensional materials are just starting to be addressed, but innovative ideas are emerging. For example, in an Article in this issue, Moon-Ho Jo and colleagues illustrate how a scanning light probe can be used to write monolithic integrated circuits For ST on two-dimensional molybdenum ditelluride (MoTe2). The researchers — who are based at the Institute for Basic Science in Pohang, Pohang University of Science and Technology, the Korea Institute of Materials Science, and Yonsei University — first pattern gold electrodes onto the MoTe2. Then, by shining the light probe (a visible laser) onto the electrodes, the semiconducting MoTe2 beneath can be converted from an n-type semiconductor to a p-type semiconductor. (With silicon CMOS technology, such doping is typically achieved using ion implantation.) The approach allows the two-dimensional material to be doped precisely and quickly, and Jo and colleagues use it to create arrays of bipolar junction transistors and circular diodes. Integrated circuits are the basis of so much of modern technology and here at Nature Electronics we aim to also consider the wider social, ethical and legal issues that surround the implementation of such technology. To this end, this issue sees the start of our Books & Arts section. Here, Arlindo Oliveira of the Instituto Superior Técnico in Portugal reviews Hello World, a book by Hannah Fry on the roles — both good and bad — that algorithms play in everyday life. Then Christiana Varnava from our editorial team reviews The Future Starts Here, an exhibition at the Victoria and Albert Museum in London that brings together a collection of emerging technologies in order to explore the ways they could shape society in the years to come. An integrated circuit consists of capacitors, resistors, transistors, and other metallic connections required for a complete electrical circuit. The most popular electrical circuits are the MOSFET circuits because the switching time can be easily reduced. In addition, the transistors switch faster if the devices are made smaller. However, it is important to keep in check the power dissipated by a transistor so that the amount of heat produced in an integrated circuit can be kept under control. Due to the improvement of the technology in building integrated circuits, primarily due to the decrease in the individual devices as well as in the increase in the area of the circuit, there has been a rapid growth in the number of transistors on an integrated circuit since the first such circuit was fabricated in 1961 with only four transistors. At present, a typical integrated circuit For TI has about 80 million transistors. The single most important criterion is to keep in check the enormous heat produced by such circuits. The ICs or chips used in a PCB do various tasks, such as signal acquisition, transformation, processing, and transfer. Some of these chips (for example, an encryption or image compression chip) work on digital signals and are called digital ICs, whereas others work on analog or both types of signals, and called analog/mixed-signal (AMS) chips. Examples of the latter type include voltage regulators, power amplifiers, and signal converters. The ICs can also be classified based on their usage model and availability in the market. Application-specific integrated circuits (ASIC) represent a class of ICs, which contain customized functionalities, such as signal processing or security functions, and meet specific performance targets that are not readily available in the market. On the other hand, commercial off-the-shelf (COTS) ICs are the ones, which are already available in the market, often providing flexibility and programmability to support diverse system design needs. These products can be used out-of-the-box, but often needs to be configured for a target application. Examples of COTS components include field programmable gate arrays (FPGA), microcontrollers/processors, and data converters. The distinction between ASIC and COTS is often subtle, and when a chip manufacturer decides to sell its ASICs into the market, they can become “off-the-shelf” to the original equipment manufacturers (OEMs), who build various computing systems using them. To develop integrated circuits, we need to accelerate the development of bases in both north and south China, and begin establishing research and production consortiums spread over Shanghai, Wuxi, and Shaoxing to create the conditions for large-scale development during the Seventh Five-Year Program period. Before 1985, we need to focus on mastering the technology for industrialized mass production of small- and medium-scale integrated circuits and achieving a breakthrough in the technology for the industrialized mass production of medium- and low-grade, large-scale integrated circuits. We need to strive to solve the difficult problem of ensuring the quality of small- and medium-scale integrated circuits having anywhere from several tens up to a thousand components on a wafer produced on a large production line and do everything possible to increase yield and decrease the failure rate. Products made in accordance with the seven special standards1 should have tolerances of 10?7 m and consumer electronics should have tolerances of 10?6 m. In addition, one or two production lines should have the capacity to produce more than 10 million items per year and the whole country should be able to produce 50 million per year at a cost that enables them to sell at the same price that imported integrated circuits cost in the late 1970s. We need to attain stable batch production of circuits for memory, 4- and 8-bit microcomputers, computers, instruments and meters, communications equipment, electronic clocks and watches, and TV speakers, all of which have a degree of integration of around 10,000 components, and we need to produce a total of 3–5 million of them per year. At the same time, we need to actively carry out R&D on high-grade, large- and very-large-scale integrated circuits. We need to finalize the design of 16K single-supply NMOS dynamic memory cells and 4K CMOS static memory cells and put them into production, and build satisfactory prototypes of 16K NMOS static memory cells, 64K NMOS dynamic memory cells, 16-bit microprocessor circuits, and ultra-high speed GaAs circuits.The worldwide development of integrated circuits has become more rapid, and a new generation seems to emerge almost every 3 years. Science and technology have achieved astonishing progress over the 20th century, and the next century will bring even greater breakthroughs in the areas of physical science, information science, bioengineering, materials science, cosmology, and environmental science. While developing new and high technologies and the industries using them, it is necessary not only to do good R&D work but also to take care to build a complete set of effective mechanisms. If China wants to develop a technology or product, it must consider the market for it. Without the impetus of market demand, it is very difficult to develop. The country should consider the development of integrated circuits. One major problem is that a few foreign companies have a huge share of Chinese electronic products market. Integrated circuits in these electronic products find their way to China installed in import equipment. The country does not have a market for the integrated circuits they produce, so there is no way to mass produce them.
Дата Публикации: 17-11-21
Engineering Essentials: Fundamentals of Hydraulic Pumps
Описание: Engineering Essentials: Fundamentals of Hydraulic Pumps When a hydraulic pump operates, it performs two functions. First, its mechanical action creates a vacuum at the pump inlet which allows atmospheric pressure to force liquid from the reservoir into the inlet line to the pump. Second, its mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system. A pump produces liquid movement or flow: it does not generate pressure. It produces the flow necessary for the development of pressure which is a function of resistance to fluid flow in the system. For example, the pressure of the fluid at the pump outlet is zero for a pump not connected to a system (load). Further, for a pump delivering into a system, the pressure will rise only to the level necessary to overcome the resistance of the load. Classification of pumps All pumps may be classified as either positive-displacement or non-positive-displacement. Most pumps used in hydraulic systems are positive-displacement. A non-positive-displacement pump produces a continuous flow. However, because it does not provide a positive internal seal against slippage, its output varies considerably as pressure varies. Centrifugal and propeller pumps are examples of non-positive-displacement pumps. If the output port of a non-positive-displacement pump were blocked off, the pressure would rise, and output would decrease to zero. Although the pumping element would continue moving, flow would stop because of slippage inside the pump. In a positive-displacement pump, slippage is negligible compared to the pump's volumetric output flow. If the output port were plugged, pressure would increase instantaneously to the point that the pump's pumping element or its case would fail (probably explode, if the drive shaft did not break first), or the pump's prime mover would stall. Positive-displacement principle A positive-displacement pump is one that displaces (delivers) the same amount of liquid for each rotating cycle of the pumping element. Constant delivery during each cycle is possible because of the close-tolerance fit between the pumping element and the pump case. That is, the amount of liquid that slips past the pumping element in a positive-displacement pump is minimal and negligible compared to the theoretical maximum possible delivery. The delivery per cycle remains almost constant, regardless of changes in pressure against which the pump is working. Note that if fluid slippage is substantial, the harvester hydraulic pump is not operating properly and should be repaired or replaced. Positive-displacement pumps can be of either fixed or variable displacement. The output of a fixed displacement pump remains constant during each pumping cycle and at a given pump speed. The output of a variable displacement pump can be changed by altering the geometry of the displacement chamber. Other names to describe these pumps are hydrostatic for positive-displacement and hydrodynamic pumps for non-positive-displacement. Hydrostatic means that the pump converts mechanical energy to hydraulic energy with comparatively small quantity and velocity of liquid. In a hydrodynamic pump, liquid velocity and movement are large; output pressure actually depends on the velocity at which the liquid is made to flow. Reciprocating pumps Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2015 02 Pumps1 Figure 1. Reciprocating pump. The positive-displacement principle is well illustrated in the reciprocating-type pump, the most elementary positive-displacement gear pump, Figure 1. As the piston extends, the partial vacuum created in the pump chamber draws liquid from the reservoir through the inlet check valve into the chamber. The partial vacuum helps seat firmly the outlet check valve. The volume of liquid drawn into the chamber is known because of the geometry of the pump case, in this example, a cylinder. As the piston retracts, the inlet check valve reseats, closing the valve, and the force of the piston unseats the outlet check valve, forcing liquid out of the pump and into the system. The same amount of liquid is forced out of the pump during each reciprocating cycle. All positive-displacement pumps deliver the same volume of liquid each cycle (regardless of whether they are reciprocating or rotating). It is a physical characteristic of the pump and does not depend on driving speed. However, the faster a pump is driven, the more total volume of liquid it will deliver. Rotary pumps In a rotary-type pump, rotary motion carries the liquid from the pump inlet to the pump outlet. Rotary pumps are usually classified according to the type of element that transmits the liquid, so that we speak of a gear-, lobe-, vane-, or piston-type rotary pump. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig2 Figure 2. Spur gear pump. External-gear pumps can be divided into external and internal-gear types. A typical external-gear pump is shown in Figure 2. These pumps come with a straight spur, helical, or herringbone gears. Straight spur gears are easiest to cut and are the most widely used. Helical and herringbone gears run more quietly, but cost more. A gear pump produces flow by carrying fluid in between the teeth of two meshing gears. One gear is driven by the drive shaft and turns the idler gear. The chambers formed between adjacent gear teeth are enclosed by the pump housing and side plates (also called wear or pressure plates). A partial vacuum is created at the pump inlet as the gear teeth unmesh. Fluid flows in to fill the space and is carried around the outside of the gears. As the teeth mesh again at the outlet end, the fluid is forced out. Volumetric efficiencies of gear pumps run as high as 93% under optimum conditions. Running clearances between gear faces, gear tooth crests and the housing create an almost constant loss in any pumped volume at a fixed pressure. This means that volumetric efficiency at low speeds and flows is poor, so that gear pumps should be run close to their maximum rated speeds. Although the loss through the running clearances, or "slip," increases with pressure, this loss is nearly constant as speed and output change. For one pump the loss increases by about 1.5 gpm from zero to 2,000 psi regardless of speed. Change in slip with pressure change has little effect on performance when operated at higher speeds and outputs. External-gear pumps are comparatively immune to contaminants in the oil, which will increase wear rates and lower efficiency, but sudden seizure and failure are not likely to occur. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig3 Figure 3. Lobe pump. The lobe pump is a rotary, external-gear pump, Figure 3. It differs from the conventional external-gear pump in the way the "gears" are driven. In a gear pump, one gear drive the other; in a lobe pump, both lobes are driven through suitable drives gears outside of the pump casing chamber. A screw pump is an axial-flow gear pump, similar in operation to a rotary screw compressor. Three types of screw pumps are the single-screw, two-screw, and three-screw. In the single-screw pump, a spiraled rotor rotates eccentrically in an internal stator. The two-screw pump consists of two parallel intermeshing rotors rotating in a housing machined to close tolerances. The three-screw pump consists of a central-drive rotor with two meshing idler rotors; the rotors turn inside of a housing machined to close tolerances. Flow through a screw pump is axial and in the direction of the power rotor. The inlet hydraulic fluid that surrounds the rotors is trapped as the rotors rotate. This fluid is pushed uniformly with the rotation of the rotors along the axis and is forced out the other end. The fluid delivered by a screw pump does not rotate, but moves linearly. The rotors work like endless pistons, which continuously move forward. There are no pulsations even at higher speed. The absence of pulsations and the fact that there is no metal-to-metal contact results in very quiet operation. Larger pumps are used as low-pressure, large-volume prefill pumps on large presses. Other applications include hydraulic systems on submarines and other uses where noise must be controlled. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig4 Figure 4. Internal-gear pumps - gerotor and crescent. Internal-gear pumps, Figure 4, have an internal gear and an external gear. Because these pumps have one or two less teeth in the inner gear than the outer, relative speeds of the inner and outer gears in these designs are low. For example, if the number of teeth in the inner and outer gears were 10 and 11 respectively, the inner gear would turn 11 revolutions, while the outer would turn 10. This low relative speed means a low wear rate. These pumps are small, compact units. The crescent seal internal-gear pump consists of an inner and outer gear separated by a crescent-shaped seal. The two gears rotate in the same direction, with the inner gear rotating faster than the outer. The hydraulic oil is drawn into the pump at the point where the gear teeth begin to separate and is carried to the outlet in the space between the crescent and the teeth of both tears. The contact point of the gear teeth forms a seal, as does the small tip clearance at the crescent. Although in the past this pump was generally used for low outputs, with pressures below 1,000 psi, a 2-stage, 4,000-psi model has recently become available. The gerotor internal-gear pump consists of a pair of gears which are always in sliding contact. The internal gear has one more tooth than the gerotor gear. Both gears rotate in the same direction. Oil is drawn into the chamber where the teeth are separating, and is ejected when the teeth start to mesh again. The seal is provided by the sliding contact. Generally, the internal-gear pump with toothcrest pressure sealing has higher volumetric efficiency at low speeds than the crescent type. Volumetric and overall efficiencies of these pumps are in the same general range as those of external-gear pumps. However, their sen In vane pumps, a number of vanes slide in slots in a rotor which rotates in a housing or ring. The housing may be eccentric with the center of the rotor, or its shape may be oval, Figure 5. In some designs, centrifugal force holds the vanes in contact with the housing, while the vanes are forced in and out of the slots by the eccentricity of the housing. In one vane pump, light springs hold the vanes against the housing; in another pump design, pressurized pins urge the vanes outward. During rotation, as the space or chamber enclosed by vanes, rotor, and housing increases, a vacuum is created, and atmospheric pressure forces oil into this space, which is the inlet side of the pump. As the space or volume enclosed reduces, the liquid is forced out through the discharge ports. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig6 Figure 6. Balanced vane pump. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig7 Figure 7. Variable-displacement, pressure-compensated vane pump. Balanced and unbalanced vane pumps — The pump illustrated in Figure 5 is unbalanced, because all of the pumping action occurs in the chambers on one side of the rotor and shaft. This design imposes a side load on the rotor and drive shaft. This type vane pump has a circular inner casing. Unbalanced vane pumps can have fixed or variable displacements. Some vane pumps provide a balanced construction in which an elliptical casing forms two separate pumping areas on opposite sides of the rotor, so that the side loads cancel out, Figure 6. Balanced vane pumps come only in fixed displacement designs. In a variable-volume unbalanced design, Figure 7, the displacement can be changed through an external control such as a handwheel or a pressure compensator. The control moves the cam ring to change the eccentricity between the ring and rotor, thereby changing the size of the pumping chamber and thus varying the displacement per revolution. When pressure is high enough to overcome the compensator spring force, the cam ring shifts to decrease the eccentricity. Adjustment of the compensator spring determines the pressure at which the ring shifts. Because centrifugal force is required to hold the vanes against the housing and maintain a tight seal at those points, these pumps are not suited for low-speed service. Operation at speeds below 600 rpm is not recommended. If springs or other means are used to hold vanes out against the ring, efficient operation at speeds of 100 to 200 rpm is possible. Vane pumps maintain their high efficiency for a long time, because compensation for wear of the vane ends and the housing is automatic. As these surfaces wear, the vanes move further out in their slots to maintain contact with the housing. Vane pumps, like other types, come in double units. A double pump consists of two pumping units in the same housing. They may be of the same or different sizes. Although they are mounted and driven like single pumps, hydraulically, they are independent. Another variation is the series unit: two pumps of equal capacity are connected in series, so that the output of one feeds the other. This arrangement gives twice the pressure normally available from this pump. Vane pumps have relatively high efficiencies. Their size is small relative to output. Dirt tolerance is relatively good. Piston pumps Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig8 Figure 8. Axial-piston pump varies displacement by changing angle of swashplate. The piston pump is a rotary unit which uses the principle of the reciprocating pump to produce fluid flow. Instead of using a single piston, these pumps have many piston-cylinder combinations. Part of the pump mechanism rotates about a drive shaft to generate the reciprocating motions, which draw fluid into each cylinder and then expels it, producing flow. There are two basic types, axial and radial piston; both area available as fixed and variable displacement pumps. The second variety often is capable of variable reversible (overcenter) displacement. Most axial and radial piston pumps lend themselves to variable as well as fixed displacement designs. Variable displacement pumps tend to be somewhat larger and heavier, because they have added internal controls, such as handwheel, electric motor, hydraulic cylinder, servo, and mechanical stem. Axial-piston pumps — The pistons in an axial piston pump reciprocate parallel to the centerline of the drive shaft of the piston block. That is, rotary shaft motion is converted into axial reciprocating motion. Most axial piston pumps are multi-piston and use check valves or port plates to direct liquid flow from inlet to discharge. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig9 Figure 9. Radial piston pump. Inline piston pumps — The simplest type of axial piston pump is the swashplate design in which a cylinder block is turned by the drive shaft. Pistons fitted to bores in the cylinder block are connected through piston shoes and a retracting ring, so that the shoes bear against an angled swashplate. As the block turns, Figure 8, the piston shoes follow the swashplate, causing the pistons to reciprocate. The ports are arranged in the valve plate so that the pistons pass the inlet as they are pulled out and the outlet as they are forced back in. In these pumps, displacement is determined by the size and number of pistons as well as their stroke length, which varies with the swashplate angle. In variable-displacement models of the inline pump, the swashplate swings in a movable yoke. Pivoting the yoke on a pintle changes the swashplate angle to increase or decrease the piston stroke. The yoke can be positioned with a variety of controls, i.e., manual, servo, compensator, handwheel, etc. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig10 Figure 10. Pressure-flow curve of fixed-displacement oil hydraulic pump. Bent-axis pumps — This pump consists of a drive shaft which rotates the pistons, a cylinder block, and a stationary valving surface facing the cylinder block bores which ports the inlet and outlet flow. The drive shaft axis is angular in relation to the cylinder block axis. Rotation of the drive shaft causes rotation of the pistons and the cylinder block. Because the plane of rotation of the pistons is at an angle to the valving surface plane, the distance between any one of the pistons and the valving surface continually changes during rotation. Each individual piston moves away from the valving surface during one-half of the shaft revolution and toward the valving surface during the other half. The valving surface is so ported that its inlet passage is open to the cylinder bores in that part of the revolution where the pistons move away. Its outlet passage is open to the cylinder bores in the part of the revolution where the pistons move toward the valving surface. Therefore, during pump rotation the pistons draw liquid into their respective cylinder bores through the inlet chamber and force it out through the outlet chamber. Bent axis pumps come in fixed and variable displacement configurations, but cannot be reversed. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig11 Figure 11. Pressure flow curve of variable-displacement hydraulic oil transfer pump with ideal flow and pressure compensation. In radial-piston pumps, the pistons are arranged radially in a cylinder block; they move perpendicularly to the shaft centerline. Two basic types are available: one uses cylindrically shaped pistons, the other ball pistons. They may also be classified according to the porting arrangement: check valve or pintle valve. They are available in fixed and variable displacement, and variable reversible (over-center) displacement. In pintle-ported radial piston pump, Figure 9, the cylinder block rotates on a stationary pintle and inside a circular reacting ring or rotor. As the block rotates, centrifugal force, charging pressure, or some form of mechanical action causes the pistons to follow the inner surface of the ring, which is offset from the centerline of the cylinder block. As the pistons reciprocate in their bores, porting in the pintle permits them to take in fluid as they move outward and discharge it as they move in. The size and number of pistons and the length of their stroke determine pump displacement. Displacement can be varied by moving the reaction ring to increase or decrease piston travel, varying eccentricity. Several controls are available for this purpose. Hydraulicspneumatics Com Sites Hydraulicspneumatics com Files Uploads 2014 04 Fig12 Figure 12. Schematic of typical proportional pump pressure compensator control. Plunger pumps are somewhat similar to rotary piston types, in that pumping is the result of pistons reciprocating in cylinder bores. However, the cylinders are fixed in these pumps; they do not rotate around the drive shaft. Pistons may be reciprocated by a crankshaft, by eccentrics on a shaft, or by a wobble plate. When eccentrics are used, return stroke is by springs. Because valving cannot be supplied by covering and uncovering ports as rotation occurs, inlet and outlet check valves may be used in these pumps. Because of their construction, these pumps offer two features other pumps do not have: one has a more positive sealing between inlet and outlet, permitting higher pressures without excessive leakage of slip. The other is that in many pumps, lubrication of moving parts other than the piston and cylindrical bore may be independent of the liquid being pumped. Therefore, liquids with poor lubricating properties can be pumped. Volumetric and overall efficiencies are close to those of axial and radial piston pumps. Measuring pump performance Volume of fluid pumped per revolution is calculated from the geometry of the oil-carrying chambers. A pump never quite delivers the calculated, or theoretical, amount of fluid. How close it comes is called volumetric efficiency. Volumetric efficiency is found by comparing the calculated delivery with actual delivery. Volumetric efficiency varies with speed, pressure, and the construction of the pump. A pump's mechanical efficiency is also less than perfect, because some of the input energy is wasted in friction. Overall efficiency of a hydraulic oil pressure pump is the product of its volumetric and mechanical efficiencies. Pumps are generally rated by their maximum operating pressure capability and their output, in gpm or lpm, at a given drive speed, in rpm. Pressure compensation and load sensing are terms often used to describe pump features that improve the efficiency of pump operation. Sometimes these terms are used interchangeably, a misconception that is cleared up once you understand the differences in how the two enhancements operate. To investigate these differences, consider a simple circuit using a fixed-displacement pump running at constant speed. This circuit is efficient only when the load demands maximum power because the pump puts out full pressure and flow regardless of load demand. A relief valve prevents excessive pressure buildup by routing high-pressure fluid to tank when the system reaches the relief setting. As Figure 10 shows, power is wasted whenever the load requires less than full flow or full pressure. The unused fluid energy produced by the pump becomes heat that must be dissipated. Overall system efficiency may be 25% or lower. Variable displacement pumps, equipped with displacement controls, Figure 11, can save most of this wasted hydraulic horsepower when moving a single load. Control variations include hand wheel, lever, cylinder, stem servo, and electrohydraulic servo controls. Examples of displacement control applications are the lever-controlled hydrostatic transmissions used to propel windrowers, skid-steer loaders, and road rollers. While matching the exact flow and pressure needs of a single load, these controls have no inherent pressure or power-limiting capabilities. And so, other provisions must be made to limit maximum system pressure, and the prime mover still must have corner horsepower capability. Moreover, when a pump supplies a circuit with multiple loads, the flow and pressure-matching characteristics are compromised. A design approach to the system in which one pump powers multiple loads is to use a pump equipped with a proportional pressure compensator, Figure 12. A yoke spring biases the pump swashplate toward full displacement. When load pressure exceeds the compensator setting, pressure force acts on the compensator spool to overcome the force exerted by the spring. The spool then shifts toward the compensator-spring chamber, ports pump output fluid to the stroking piston, and decreases pump displacement. The compensator spool returns to neutral when pump pressure matches the compensator spring setting. If a load blocks the actuators, pump flow drops to zero. Using a variable-displacement, pressure-compensated pump rather than a fixed-displacement pump reduces circuit horsepower requirements dramatically, Figure 13. Output flow of this type of pump varies according to a predetermined discharge pressure as sensed by an orifice in the pump's compensator. Because the compensator itself operates from pressurized fluid, the discharge pressure must be set higher - say, 200 psi higher - than the maximum load-pressure setting. So if the load-pressure setting of a pressure-compensated pump is 1,100 psi, the pump will increase or decrease its displacement (and output flow) based on a 1,300-psi discharge pressure. A two-stage pressure-compensator control, Figure 14, uses pilot flow at load pressure across an orifice in the main stage compensator spool to create a pressure drop of 300 psi. This pressure drop generates a force on the spool which is opposed by the main spool spring. Pilot fluid flows to tank through a small relief valve. A spring chamber pressure of 4,700 psi provides a compensator control setting of 5,000 psi. An increase in pressure over the compensator setting shifts the main stage spool to the right, porting pump output fluid to the stroking piston, which overcomes bias piston force and reduces pump displacement to match load requirements. The earlier stated misconception stems from an observation that output pressure from a pressure-compensated pump can fall below the compensator setting while an actuator is moving. This does not happen because the pump is sensing the load, it happens because the pump is undersized for the application. Pressure drops because the pump cannot generate enough flow to keep up with the load. When properly sized, a pressure-compensated pump should always force enough fluid through the compensator orifice to operate the compensator.
Дата Публикации: 17-11-21
What is a 3-Phase Motor and How Does it Work?
Описание: What is a 3-Phase Motor and How Does it Work? What is a 3-Phase Motor and How Does it Work? Three-phase motors (also annotated numerically as 3-phase motors) are widely used in industry and have become the workhorse of many mechanical and electromechanical systems because of their relative simplicity, proven reliability, and long service life. Three-phase motors are one example of a type of induction motor, also known as an asynchronous motor, that operates using the principals of electromagnetic induction. While there are also single-phase induction motors available, those types of induction motors are used less frequently in industrial applications but are widely used in domestic applications such as in vacuum cleaners, refrigerator compressors, and air conditioners, owing to the use of single-phase AC power in homes and offices. In this article, we will discuss what a three-phase motor is and describe how it operates. To access other resources about motors, consult one of our other motor guides covering AC motors, DC motors, Induction motors, or the more general article on the types of motors. A full list of related motor articles is found in the section on related articles. To understand single phase motor, it is useful to first understand three-phase power. In electrical power generation, alternating current (AC) that is created by a generator has the characteristic that its amplitude and direction changes with time. If shown graphically with the amplitude on the y-axis and time on the x-axis, the relationship between the voltage or current vs. time would resemble a sine wave as shown below: Electrical power carried to homes is single-phase, meaning that there is one current-carrying conductor plus a neutral connection and a ground connection. In three-phase power, which is used in industrial and commercial settings to run larger machinery that has greater power needs, there are three conductors of electrical current, each of which is operating at a phase difference of 120o of 2π/3 radians apart. If viewed graphically, each phase would appear as a separate sine wave, which then combines as shown in the image below: Three-phase motors are powered from the electrical voltage and current that is generated as three-phase input power and is then used to produce mechanical energy in the form of a rotating motor shaft. What is a 3-Phase Motor? Three-phase motors are a type of AC motor that is a specific example of a reducer motor. These motors can be either an induction motor (also called an asynchronous motor) or a synchronous motor. The motors consist of three main components – the stator, the rotor, and the enclosure. The stator consists of a series of alloy steel laminations around which are wound with wire to form induction coils, one coil for each phase of the electrical power source. The stator coils are energized from the three-phase power source. The rotor also contains induction coils and metal bars connected to form a circuit. The rotor surrounds the motor shaft and is the motor component that rotates to produce the mechanical energy output of the motor. The enclosure of the motor holds the rotor with its motor shaft on a set of bearings to reduce the friction of the rotating shaft. The enclosure has end caps that hold the bearing mounts and house a fan that is attached to the motor shaft which spins as the motor shaft turns. The spinning fan draws ambient air from outside the enclosure and forces the air across the stator and rotor to cool the motor components and dissipate heat that is generated in the various coils from the coil resistance. The enclosure also typically has raised mechanical fins on the exterior that serve to further conduct heat to the outside air. The end cap will also provide a location to house the electrical connections for the three-phase power to the motor. How does a 3-Phase Motor Work? Three-phase motors operate by the principle of electromagnetic induction which was discovered by the English physicist Michael Faraday back in 1830. Faraday noticed that when a conductor such as a coil or loop of wire, is placed in a changing magnetic field, there is an induced electromotive force or EMF that is generated in the conductor. He also observed that current flowing in a conductor such as wire will generate a magnetic field and that the magnetic field will vary as the current in the wire changes in either magnitude or dir These principles form the basis for understanding how a three phase induction motor works. Figure 3 below is an illustration of Faraday's law of induction. Note that the presence of an EMF depends on the motion of the magnet which results in a changing magnetic field to exist. For induction motors, when the stator is powered from a three-phase electrical energy source, each coil generates a magnetic field whose poles (north or south) change position as the AC current oscillates through a complete cycle. Since each of the three phases of the AC current are phase-shifted by 120o, the magnetic polarity of the three coils are not all identical at the same instant of time. This condition results in the stator producing what is known as an RMF or Rotating Magnetic Field. As the rotor sits in the center of the stator coils, the changing magnetic field from the stator induces a current in the rotor coils, which in turn results in an opposing magnetic field being generated by the rotor. The rotor field seeks to align its polarity against that of the stator field, the result being a net torque is applied to the motor shaft and it begins to rotate as it seeks to bring its field into alignment. Note that in the 3-phase induction motor, there is no direct electrical connection to the rotor; magnetic induction causes the motor rotation. With three-phase induction motors, the rotor seeks to maintain alignment with the RMF of the stator, but never achieves it, which is why induction motors are also called asynchronous motors. where Nr is the speed of the rotor, and Ns is the synchronous speed of the rotating field (RMF) of the stator. Synchronous motors operate in a similar fashion to induction motors except that in the case of a synchronous motor, the stator and rotor fields are locked into alignment so that the stator RMF will cause the rotor to turn at the exact same rate of rotation (in synch – therefore the slip is equal to 0). For more information on how this is accomplished, refer to these articles on reluctance motors and brushless DC motors. Note that synchronous motors, unlike induction motors, need not be powered by AC power. Motor Controllers for 3-Phase Motors The speed that is generated by a 3-phase AC motor is a function of the AC supply frequency since it is the source of the RMF in the stator coils. Therefore, some AC motor controllers operate by using the AC current input to generate a modulated or controlled frequency input to the motor, thereby controlling the speed of the motor. Another approach that can be used to control motor speed is by altering the slip (described earlier). If the slip increases, the motor speed (i.e. the speed of the rotor) decreases. To learn more about the approaches for motor control, review our article on AC Motor Controllers. Summary This article presented a brief discussion of what 3-phase motors are and how they operate. To learn more about motors, explore our related articles listed below. For information on other products, consult our additional guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products. The first concept we need to understand about a 3 phase induction motor is the first part of its name – 3 phase power. A single phase power supply uses two wires to provide a sinusoidal voltage. In a three phase system, three wires are used to provide the same sinusoidal voltage, but each phase is shifted by 120°. At any point in time if you were to add up the voltage of each phase, the sum would be constant. Single phase power is fine for residential or other low power applications, but three phase power is typically required for industrial or higher power applications. This is because it can transmit three times as much power while only using 1.5 times as much wire. This makes for a more efficient and economical power supply. Induction motors offer many advantages, including reduced upfront and maintenance costs. Because of their basic, economical design, induction machines usually cost less than synchronous and dc motors. This makes them an ideal choice for industrial, fixed speed applications like wind power and wind turbine generators. The sheer simplicity of induction motors also makes maintenance easier and less frequent, decreasing operating costs over time. This cost efficiency gives induction machines a significant edge over synchronous and dc motors, which feature many additional components, like slip rings, commutators, and brushes. Durability is another strength of induction motors. These rugged machines can run for several years with little attention and maintenance, even in demanding environments. The absence of brushes (and sparks) allows induction motors to operate safely in explosive or other environmental conditions, creating a flexible solution for Oil & Gas, material handling, and more. 3 phase induction motors bear unique advantages as well, including self-starting torque. This feature eliminates the need for starting capacitors, which are typically required for a single phase motors. 3 phase machines also deliver exceptional speed regulation and overload capacity, making them viable for a wide range of applications.
Дата Публикации: 17-11-21