Relatively safe and environmentally benign working fluids can be used.
The term "champagne heat pump" denotes a developmental heat pump that exploits a cycle of absorption and desorption of carbon dioxide in an alcohol or other organic liquid. Whereas most heat pumps in common use in the United States are energized by mechanical compression, the champagne heat pump is energized by heating.
The concept of heat pumps based on other absorption cycles energized by heat has been understood for years, but some of these heat pumps are outlawed in many areas because of the potential hazards posed by leakage of working fluids. For example, in the case of the water/ammonia cycle, there are potential hazards of toxicity and flammability.
The organic-liquid/carbon dioxide absorption/desorption cycle of the champagne heat pump is similar to the water/ammonia cycle, but carbon dioxide is nontoxic and environmentally benign, and one can choose an alcohol or other organic liquid that is also relatively nontoxic and environmentally benign. Two candidate nonalcohol organic liquids are isobutyl acetate and amyl acetate. Although alcohols and many other organic liquids are flammable, they present little or no flammability hazard in the champagne heat pump because only the nonflammable carbon dioxide component of the refrigerant mixture is circulated to the evaporator and condenser heat exchangers, which are the only components of the heat pump in direct contact with air in habitable spaces.
The champagne heat pump (see figure) includes a generator — essentially a heated pressure vessel — wherein a solution of carbon dioxide in the absorbent liquid is heated to generate pressurized carbon dioxide. In a typical application, the solution is heated to a temperature of 250 °F (121 °C), causing the carbon dioxide to be desorbed at a pressure of about 1.4 kpsi (9.7 MPa). The carbon dioxide is precooled, typically to about 100 °F (38 °C) while at this high pressure, then expanded to a pressure of about 560 psi (3.9 MPa); this expansion provides cooling to about 40 °F (4 °C). The carbon dioxide then passes back through a heat exchanger to an absorber, which is another pressure vessel wherein the carbon dioxide goes back into solution, releasing heat. A pump circulates the solution between the generator and absorber.
Carbon dioxide can be an excellent refrigerant fluid for automobiles because its critical temperature is only about 88 °F (31 °C). Therefore, precooling prior to expansion can take place over a relatively wide supercritical temperature range; in contrast, the common refrigerant 134a must be condensed at one specific temperature for a given pressure.
A research group in Norway has produced mechanically actuated carbon dioxide vapor-compression air conditioners for automobiles and has shown those air conditioners to be more efficient and potentially lighter than are comparable air conditioners based on a chlorofluorocarbon refrigerant fluid. The champagne heat pump goes beyond the Norwegian research by replacing mechanical actuation with heat actuation. Potential applications (other than automotive air conditioning) for the champagne heat pump include home and industrial heating and cooling.
Carbon Dioxide Is Absorbed and Desorbed in a thermodynamic cycle similar to that of a water/ammonia heat pump. The champagne heat pump is so named because the desorption part of its operating cycle is reminiscent of carbon dioxide effervescing out of alcohol-containing champagne.
This work was done by Jack A. Jones of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Physical Sciences category.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, NASA Management Office–JPL; (818) 354-7770. Refer to NPO-19855.
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