Abstract
The main purpose of this work is to enhance the energy efficiency of CO2 automobile air conditioning system. Theoretical analysis demonstrated that the mixture of CO2 and propane can improve its performance, thus, experiments have been carried out to see effects of various CO2-propane mass fractions of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 on the system performance at different ambient temperatures and gas cooler frontal air velocities. Experimental results show similar trends with those from the theoretical results. It has been shown that under the same compressor speed, system COP reaches highest at 60% of CO2 mass fraction, which is 29.4% higher than pure CO2 system and even achieves equal level of the R134a system, the optimum pressure and discharge temperature are reduced up to a maximum of 40% and 47 °C during the research range. Furthermore, comparison was carried out under the same cooling capacity by adjusting compressor speed for different mass fraction of CO2, results demonstrate that the use of CO2-propane mixtures yields a maximum COP rise of 22%even when cooling capacity is kept constant. A new optimum high pressure control algorithm for the transcritical CO2-propane mixture cycle has been developed based on the experimental data within a deviation of 5%.
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