Performance evaluation of household refrigerators running with R600a contaminated with non-condensable gases.
Abstract This article reports an experimental study of performance degradation and expansion noise generation in a household refrigerator running with isobutane contaminated with non-condensable gases (NCGs). Controlled amounts of nitrogen were injected into the system using a purpose-built device. The refrigerant flow at the capillary inlet was visualized while an accelerometer recorded the expansion noise at the evaporator inlet. Steady-state performance tests were carried with different nitrogen contamination levels at various compressor speeds. A high sub-cooling degree and an increased discharge pressure showed to be strong evidences of the presence of non-condensable gases. Even though the thermodynamic variables reached steady-state conditions, large fluctuations were observed for the flow pattern at the capillary tube inlet and in the acceleration readings. Therefore, standardized cyclic energy consumption and pull-down tests were also conducted to evaluate the effect of NCGs on the refrigerator transients. It was noticed that the energy consumption increased up to 25.9% when the system was doped with a mass fraction of 0.43% of N2. Also, a quasi-linear increase of the energy consumption with the N2 mass fraction was observed. Furthermore, the system pull-down time increased by up to 10-h due to NCG contamination. A visual inspection revealed that the performance degradation was related to a partial clogging of the capillary tube that unbalanced the compressor and expansion device mass flow rates, preventing the system to reach steady-state conditions.