Numerical analysis of pressure variation and gas load effects in the refrigeration system for household refrigerators

Abstract

Insufficient air evacuation from a refrigeration system prior to refrigerant charging can lead to an increased non-condensable gas concentration, negatively impacting system performance. Despite its critical importance, literature on refrigeration system vacuuming procedures is notably lacking. This study developed numerical methods and constitutive models to assess gas load, validated against measured pressures using experimental setups. The model developed can be extended and applied to a wide range of vacuum systems. Examining the vacuuming process in a household refrigerator, a connected vacuum pump expedited the process, revealing higher pressures in the capillary tube and condenser outlet due to low flow conductance. The rate of pressure increase attributable to the gas load from outgassing and degassing remained below 0.6 %, deemed negligible during vacuum pump operation. A 24-hour simulation post-vacuum pump cessation showcased pressure equalization and subsequent rise due to outgassing and degassing, resulting in a 201 % increase in pressure within the compressor’s internal space connected to the process pipe. The pressure increase in the compressor attributable to outgassing amounted to 140 %, surpassing the 59 % from degassing. Notably, assuming a 3 μm crack in the process pipe led to a continuous increase in refrigerator system pressure over 24 h. Leakage significantly increases the amount of non-condensable gases inside the system, potentially leading to increased energy consumption and deterioration in system performance.