Figure 1. Evaporator or Condenser sheets
PNNL researchers are developing a miniature heat pump for a range of distributed air conditioning and refrigeration applications, including air conditioning for automobiles, trucks, and watercraft. The heat pump is based on the well-established absorption cycles, using refrigerants such as lithium bromide/water or ammonia/water. The miniaturized heat pump uses the enhanced heat and mass transfer made possible by fluid flow in microchannels. Using microchannels in parallel, heat pumps can be deployed with radical reductions in size and weight compared to conventional systems. For the lithium bromide/water-absorption cycle system, the heat pump size can be reduced to 1/60th of the size needed for a comparable conventional heat pump.
Most of the components of the heat pump are embodied in metal or plastic sheets that are machined with microchannels and other features needed for a particular function. Individual sheets are used for absorption, desorption, condensation, evaporation, and heat exchange. These sheets are stacked together to form an integrated system. The addition of an external solution pump completes the structure of the heat pump.
All of the individual micro components of an absorption cycle heat pump have been demonstrated. A prototype, integrated system is currently being developed. Methods of mass production of man-portable cooling systems are being developed and evaluated.
The technology is protected by United States Patent 5,611,214 ("Microcomponent Sheet Architecture," issued March 18, 1997). Foreign patent applications based on this case and additional United States patent applications are pending.
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