Zhaogang Qi

Experimental analysis of the low-GWP refrigerant R1234yf as a drop-in replacement for R134a in a typical mobile air conditioning system

This study investigated the performance of a typical mobile air conditioning system using R134a and R1234yf as the working fluids under different working conditions. The system is composed of a microchannel parallel flow condenser, a laminated plate evaporator, a variable displacement compressor, and a thermal expansion valve. The different working cycles of each refrigerant were comprehensively compared. The optimum refrigerant charge amount of the R1234yf system was approximately 95% of the R134a system during drop-in tests. The performance of the R134a system was a little higher than that of the R1234yf system. The cooling capacity and system coefficient of performance of the R134a system were 12.4% and 9% larger, respectively. This result is mainly because of the thermophysical property differences between the two refrigerants and the improper expansion valve opening of R1234yf. Analysis on the whole cycle revealed that the R1234yf system could obtain a higher evaporating pressure and a larger superheat and subcooling. Redesigning the expansion valve for R1234yf could improve performance of the system.

Numerical Model of the Temperature Control Curve Linearity of HVAC Module in Automobile Air-Conditioning System and Applications

In the present work, a numerical model of the temperature control curve (TCC) linearity of the heating ventilating and air conditioning (HVAC) module in automobile air-conditioning system is established. The numerical model is composed of several higher precision submodels. The simulation results are validated by experimental data performed on a calorimeter test bench. It is found that the simulation data agree with the experimental data very well. The maximum deviations of the airflow rate and the temperature are 3% and 1.4°C, respectively. The factors, which influenced the TCC linearity, are numerically studied. The simulation results show that the different door configuration needs to be matched with the division type for vent ducts of the HVAC module outlet, which can decrease the temperature stratification of airflow at the outlets. Cold and hot air mixing ratio determines the slope of the linearity curve. In addition, the further the distance between the HVAC module outlet and the mixing chamber and the greater the turbulent intensity, the more the cold-hot airflow will fully mix. It contributes to the temperature uniformity at the outlets.