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 r efrigerant charge level. Due to inevitable leaks in the system, the amount of refrigerant will decrease over time and thus ultimately reduce the syste m's performance. A reduction in the amount of refrigerant charge results in excessive compressor cycling, a lower condenser pressure, a higher refrige ration 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 secon d law analysis, based on nondimensional entropy generation, is carried out to quantify the thermodynamic losses. A passenger vehicle with a cycling-cl utch, 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 t he system's thermal performance, are presented. The system's second law eff iciency increases 26% as the amount of refrigerant charge decreases by 44%. Also the individual component losses are quantified as a function of the r efrigerant charge level. The compressor and the condenser losses account fo r the largest percentage of the total losses, and are of similar magnitude. The evaporator-accumulator and the orifice tube losses account for a small er 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 compr essor, the condenser, the evaporator-accumulator, and the orifice tube decr ease 13 %, 8 %, 10 %, and 33 %, respectively. (C) 2000 Editions scientifiqu es et medicales Elsevier SAS.