An experimental analysis of the effect of refrigerant charge level on an automotive refrigeration system

The performance of an automotive refrigeration system is dependent on the refrigerant charge level. Due to inevitable leaks in the system, the amount of refrigerant will decrease over time and thus ultimately reduce the system's performance. A reduction in the amount of refrigerant charge results in excessive compressor cycling, a lower condenser pressure, a higher refrigeration temperature, and an increase in the amount of superheat. This paper identifies and quantifies the individual component losses in an automotive refrigeration system as a function of the refrigerant charge level. A second law analysis, based on nondimensional entropy generation, is carried out to quantify the thermodynamic losses. A passenger vehicle with a cycling-clutch, orifice tube refrigeration system was instrumented to measure various temperatures and pressures, and relative humidity. The data were collected at idle conditions. Thermodynamic equations, which are used to determine the system's thermal performance, are presented. The system's second law efficiency increases 26% as the amount of refrigerant charge decreases by 44%. Also the individual component losses are quantified as a function of the refrigerant charge level. The compressor and the condenser losses account for the largest percentage of the total losses, and are of similar magnitude. The evaporator-accumulator and the orifice tube losses account for a smaller percentage of the total losses, and are also of similar magnitude. With a reduction in the refrigerant charge level of 44%, the losses in the compressor, the condenser, the evaporator-accumulator, and the orifice tube decrease 13 %, 8 %, 10 %, and 33 %, respectively. (C) 2000 Editions scientifiques et medicales Elsevier SAS.