Appliance Design - April 2008 - (Page 26)

COOLING TECHNOLOGIES similar metals come in contact. Brazed construction is also used in a new series of heat exchangers from Danfoss Refrigeration & AirConditioning Div., Baltimore, Md. In 2006, Danfoss purchased Quinbao, a Chinese manufacturer of brazed heat exchangers, and now offers a variety of brazed heat exchanger models designed for applications such as HVAC, boilers, chillers and air driers. Recently, Danfoss introduced 15 models of brazed plate heat exchangers, each of which has a series of thin, A schematic of a thermoelectric cool enhanced fin. corrugated stainless-steel plates that are The technology is being developed at the University of brazed together in a vacuum furnace. Maryland. Beyond improving a heat exchanger’s tion, overall system footprint reduction and resistance to corrosion, brazed construction also improves heat transfer effi- closer approach temperatures that require ciency, says Peter D’Ambrosio, strategic glob- less water and reduce pumping costs.” The redesign of heat exchangers becomes al marketing manager-heat transfer, Danfoss. a greater challenge when developing systems The refrigerant travels through channels that are designed to induce a high degree of tur- for natural refrigerants, which have different bulence, which increases thermal efficiency physical properties and often higher operatwhile maintaining low-pressure drop. This ing pressures. For example, Coca-Cola has contributes to an increase in overall cooling pledged to place more than 6,000 vending machines charged with CO2 at the Beijing capacity, he says. The BPHE is available with three differ- Olympics this year. The company has already ent types of plate and three types of chan- moved away from CFCs and is working to nel. According to the company, the H type move to HFC-free refrigerants to CO2. The has obtuse angles that result in higher heat carbon-dioxide-based system require a heat transfer efficiency by increasing the turbu- exchanger that can handle the increased preslence of the fluid. The L-type has acute angle sures at which the CO2 operates. Giovanni that reduces the pressure drop and leads to Simeoni, head of sales and marketing, prodreduced turbulence and lower heat transfer uct development and R&D for Luvata’s efficiency. The M channel is made by one H ECO-Heatcraft division, says that the higher plate and one L plate, with both medium of volumetric efficiency of CO2 refrigerant also means that the cross-sectional area of pressure drop and heat transfer coefficient. D’Ambrosio says that designers can use pipes used in heat transfer equipment can the BPHE to replace other types of heat be reduced. “As a result,” he says, “equipment transfer technology such as shell and tube, has the potential to be smaller, lighter, more coaxial or plate and frame as well as other efficient and better for the environment.” brazed plate heat exchangers. The benefits of redesigning the system to include the BPHE are numerous, he says, including reduced footprint, reduced refrigerant charge, lower installed cost and increased efficiency and performance. D’Ambrosio says that designers should consider such factors as installed cost, as well as the total cost of ownership related to the BPHE. “Typically, systems will require much less refrigerant charge, saving a great deal of money on expensive refrigerants,” he says. “Other benefits include system piping reduc- Design help Designing or redesigning an airconditioning or refrigeration unit is challenging because of the numerous variables involved and the effects of the interactions between them. One new way to take all of these variables into account and improve the heat exchanger specifically and overall vapor compression system generally is by using a simulation software program such as the one that is offered by the University of Maryland’s Center for Environmental Energy Engineering (CEEE). The software can simulate tube-fin, microchannel, wire-fin and flat tube coils. It can examine refrigerant options, air side options, tube circuitry, using verified heat transfer and pressure drop correlations. One of its unique capabilities is the Genetic Algorithm feature that can look at various design issues such as tube length, fin density, number of fans, circuits, fan types, motor types, and other variables. It can effectively search through many thousands of design options and show the best coils that meet certain criteria such as cost, performance and overall volume. “When you ask a design engineer how many variables they can come up with, they would most likely come up with only a handful,” Reinhard Radermacher says. “But, when you consider all the possible variables and all of the combinations, it can add up fairly quickly and the options can grow into the hundreds of thousands.” The CEEE also offers also the VapCyc software, which is a vapor-compression cycle simulation and optimization tool. Different types of cycles can be considered including the basic 4-component cycle with and without suction line and two-stage split cycle and A schematic of a vapor compression cycle with TE subcooler as designed by researchers at the University of Maryland. www.applianceDESIGN.com 26 applianceDESIGN April 2008 http://www.appliancedesign.com

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Appliance Design - April 2008 Contents Editorial Shipments/Forecasts News Watch A Variant of Thermoacoustic Refrigeration Known as Acoustic-Stirling is Expanding Its Range Outside Cryocooling Into More Conventional Applications Such As Refrigeration and Air Conditioning Free-Piston, Stirling Coolers Are Now Showing Up in Mainstream Applications As Costs Come Down and Heat Transport Solutions Are Devised Heat Exchanger Innovations Are Helping To Improve the Overall Efficiency of Vapor Compression Systems Environmental Concerns Have Once Again Ignited a Debate Over Refrigerants A New Glass Ceramic Material for Induction Cooktops Can Be Decorated In a Variety of Glimmering Metallic, 3-D Looks That Can Employ a Number of Shades, Patterns, Styles, Colors, Intensities, and Textures Colorful, Reflective Coatings for Glass Create a Variety of Design Options To Help Designers Establish a Unique Look for Their Products Appliance Designers Faced With Different Motor and Drive Options Need To Understand the Differences and Tradeoffs Before Choosing A New MEMS Valve Offers a Number of Advantages Over Solenoids In Certain Applications, Including the Opportunity To Cut Energy Use The AHR Expo Set Attendance Records and Showcased Thousands of Innovative New Products Classifieds Design Marts Advertiser’s Index Association Report: CEA

Appliance Design - April 2008

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