Experimental research on charge determination and accumulator behavior in trans-critical CO2 mobile air-conditioning system.

Natural refrigerant CO 2 (R744) is one of next generation refrigerants in mobile air conditioner (MAC) application with superior environmental and heating performance. This paper investigated the charge characteristics and refrigerant migration behavior of a trans-critical CO 2 MAC. A novel visualized accumulator with five observation mirrors was adopted to set up this CO 2 MAC. A series of steady-state system experiments were carried out in a calorimeter facility to reveal the effects of refrigerant charge and EXV opening on system performance and accumulator behavior. In addition, the transient migration behavior of refrigerant during shutdown and start-up and the flow behavior of lubricant oil with 0.5 mm oil return hole were studied experimentally. It is found that a plateau region with optimal system performance occurred between 1100 g and 1600 g refrigerant charge. When the return hole becomes small, stratification of lubricant oil and liquid refrigerant was found in the accumulator. • The refrigerant migration behavior under different charge and EXV conditions was distinguished. • A plateau region between 1100 g and 1600 g charge with optimal system performance was determined. • The criteria for determining the starting and ending points of plateau region are proposed. • Unnecessary liquid refrigerant evaporation during start-up may bring rapid transient response. • Lubricant oil was stratified in the accumulator when the diameter of oil return hole was 0.5 mm. [ABSTRACT FROM AUTHOR]