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A computer program has been developed to predict the steady-state performance of vapor compression automobile air conditioners and heat pumps. The code is based on the residential heat pump model developed at the Oak Ridge National Laboratory (ORNL). Most calculations are based on fundamental physical principles, in conjunction with generalized correlations available in the research literature. Automobile air conditioning components that can be specified as input to the program include open and hermetic compressors; finned tube condensers; finned tube and plate-fin style evaporators; thermostatic expansion valves (TXV), capillary tube, and short tube expansion devices; refrigerant mass; and evaporator pressure regulator and all interconnecting tubing. Pressure drop, heat transfer rates, and latent capacity ratio for the new plate-fin evaporator submodel are shown to agree well with laboratory data. The program can be used with a variety of refrigerants, including R-134a.

For most air conditioning systems, usually only 85% of the evaporator is effectively used. The other 15% is used to superheat the refrigerant so that the compressor will be protected from liquid slugging, but this practice results in excessive evaporator volume. In mobile air conditioning (MAC) systems where the space available for the evaporator is very limited, the evaporator should be fully used, yet MAC designs have not reflected this need. This study reports on the designing and testing of a novel liquid over-feeding (LOF) MAC system that can use 100% of the evaporator effectively. A LOF system is designed so that not all liquid refrigerant is evaporated in the evaporator. The low-pressure liquid and vapor flow into an accumulator-heat exchanger where the liquid is boiled off by the warm, high-pressure liquid leaving the condenser. This concept not only allows 100% evaporator utilization, but will also reduce system power consumption and improve compressor reliability.