Effects of flash gas generation at the expansion device inlet on the dynamic characteristics of a refrigeration system

The flash gas generation at the expansion device inlet in multi-air-conditioners causes rapid reduction of refrigerant mass flow rate and irregular distribution of refrigerant into multi-indoor units. The objective of this study is to evaluate the influence of the flash gas generation on the dynamic characteristics of a refrigeration system. The dynamic characteristics of a refrigeration system with an electronic expansion valve (EEV) were measured with time at various levels of flash gas generation, which were expressed as flash gas ratio. In addition, the averaged operating parameters and system COP were investigated with the variation of flash gas ratio. As the EEV inlet condition changed from the subcooled to the two-phase state, the refrigerant flow rate decreased rapidly due to the flash gas generation at the EEV inlet. At two-phase inlet conditions, the system operating parameters, such as mass flow rate, suction and discharge pressures, fluctuated periodically with time. As the flash gas ratio increased, the average COP decreased and the discharge temperature increased, degrading the system performance and reliability more severely.