Appliance Design - April 2008 - (Page 20)

COOLING TECHNOLOGIES Graph 1. Graph 2. stage compressor, typical of that used to power a small home or hotel refrigerator would show that the Rankine system would need to be larger, heavier and use more power to perform the same job. Even if a Rankine system were available that could operate in 80 DegC ambient temperatures, it would still suffer in performance, power density and reliability when compared with the M100. These examples demonstrate the potential for the technology to serve a vast array of applications. Currently, price is the primary barrier for FPSC entry into mainstream applications. FPSC costs range from around $250 to $20,000 in low-volume production. However, when sales volumes near commodity levels, the reduced mass vs. performance ratio of the FPSC suggests eventual cost parity with conventional methods of cooling, followed by an actual cost advantage in fully automated production. Historically, the most common question about the adoption and integration of Stirling coolers pertained to the removal of the heat load from the space that requires cooling. To address this question, several methods have been refined to make the integration of the Stirling cooler simpler to accomplish and easier to service, and in ways that offer more flexibility than with Rankine systems. The simplest method for secondary heat transport is direct conduction. In its most basic form, the object to be cooled is attached to the cold side of the Stirling cooler with a direct mechanical connection. While simple and effective, this method is limited in the effective distance that heat can be transported by the physical properties of the interface material. A product example using this transport method is the CryoPorter, manufactured by the Scinics Co. of Japan. (See Fig. 11.) The Cryoporter is designed to transport and store sample vials at –80 DegC. A more advanced method for heat transport employs a fin assembly attached to the cold side of the machine with forced air circulated over the fins and then ducted to the cold chamber. This method is especially effective for minimizing temperature stratification and can be effective across broad temperature ranges, as long as the appropriate moisture control provisions are taken to ensure that ice buildup does not unduly compromise the fin assembly. A representative product using this secondary heat transport method is Twinbird’s CoolCargo. The SC-JS05 module powering the CoolCargo is designed for integration into custom insulated containers for product transport at temperatures as low as –40 DegC. The available collapsible containers come in sizes from 100 liters (4 cu. ft.) to 200 liters (8 cu. ft.) with vacuum insulation panels and expanded foam insulation respectively. A third method of secondary heat transport takes it cue from the Rankine camp and uses a liquid circulated in a loop between two heat exchangers either by the cooler itself or an independent pump. This configuration allows for the cooler to be mounted much further from the cold chamber and Graph 3. 20 applianceDESIGN April 2008 Graph 4. www.applianceDESIGN.com 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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