Appliance Design - April 2008 - (Page 23)

COOLING TECHNOLOGIES A microchannel tube and separator from Modine. The coils on a PF2 heat exchanger from Modine that has already jumped into the field is the microchannel heat exchanger (MCHX). Traditionally, round tube plate fin (RTPF) coils with mechanically bonded copper tubes and aluminum fins were the standard bearer for heat exchangers. By contrast, microchannel heat exchangers utilize aluminum construction and brazing technology. They transfer heat through multiple flat, fluidfilled tubes that have fins located between alternating layers of the tubes. Separator plates segment the coil assembly into a desuperheating and condensing section, where the refrigerant gas transitions from gas to liquid, and to a sub-cooling section where the liquid refrigerant is further cooled below its saturated temperature. The tube’s interior is segmented into a series of parallel-flow microchannels that contain the refrigerant. Similarly, a microchannel heat exchanger can be used as an evaporator. Instead of entering the heat exchanger as a superheated gas, the refrigerant enters the evaporator as two-phase mixture of liquid and gas. The air is cooled by transferring heat from the air to the refrigerant, which causes the refrigerant to evaporate. Typically the refrigerant will exit the evaporator as a single-phase gas. When acting as an evaporator, refrigerant distribution and condensate drainage are additional factors to consider. For example, Modine Mfg., Racine, Wis., a manufacturer of traditional fin-tube heat exchangers and microchannel versions, offers the PF2 coil that provides a drainage path for evaporators with vertical headers and horizontal microchannel tubes. Without this drainage path, water collects in the horizontal tubes and increases pressure drop, says Mark Johnson, product development manager for Modine. The technology was initially developed for automobiles when that industry phased out the CFC-12 refrigerant previously used and replaced it with the less effective R-134A refrigerant. The new refrigerant did not provide enough heat transfer capability, and because of size constraints, the automakers couldn’t simply increase the size of the coil. Converting to a new generation of less efficient refrigerants proved even more difficult for other cooling applications where manufacturers faced the comDanfoss’ brazed plate heat exchangers. pound challenge of meeting increased energy efficiency standards. The difficulty was such that an interim refrigerant, HCFC-22, was permitted in some applications, such as residential air conditioning, until a longer term solution was found. Faced with the mandated increase from SEER 10 to SEER 13, which became effective in January 2006, and the coming phase out of HCFC-22 in 2010, makers of air conditioners and heat pumps have expended a great deal of resources and design efforts into improving the energy efficiency of their systems. Some of those redesign involved the use of more efficient heat exchangers, and some turned to microchannel technology as part of the solution. www.applianceDESIGN.com applianceDESIGN April 2008 23 http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - April 2008

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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.