Özet:

A bench-top automobile air conditioning (AAC) system using a thermostatic expansion valve was developed. The system was equipped with a coaxial internal heat exchanger (HEX) and charged with R1234yf, a new refrigerant used as an alternative to R134a. The system was tested at the compressor speeds ranging between 1000 rpm and 2600 rpm with increments of 400 rpm. For each compressor speed, the air temperatures at the evaporator and condenser inlets were concurrently changed between 30 °C and 40 °C with increments of 5 °C. The system was operated for the cases of employing and not employing the HEX, and totally 30 test runs were performed. Then, the first law of thermodynamics was applied to the system components to evaluate various steady state performance parameters. The considered parameters were the refrigerant mass flow rate, evaporating temperature, cooling capacity, compressor power, coefficient of performance (COP), condenser heat dissipation rate and discharge temperature of the compressor. It was determined that the experimental system employing the HEX yielded on average 0.8 °C lower evaporating temperature, 2.2% higher cooling capacity, 2.0% lower compressor power and 3.0% higher COP values relative to the system not employing the HEX. These findings reveal that the use of HEX causes a better system performance in terms of the cooling capacity, compressor power and COP. Consequently, the performance of R1234yf AAC systems can be improved with the use of HEX, and thus, the AAC systems using R1234yf can be more competitive with those using R134a.

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