Visualization study of two-phase flow and noise control in a multiple temperature refrigerator during the defrost cycle

To reduce the noise caused by the flow of refrigerant during the defrost cycle and preserve the ambient sound level, this study concentrated on exploring the mechanism of noise generation in the gas–liquid separator based on visualization experiments. A transparent gas–liquid separator made of quartz glass, which was instead of the original one, was fabricated to observe the flow pattern of refrigerant in the gas–liquid separator, and the relationship between flow pattern and noise generation was investigated. The results showed that the noise is mainly generated during the defrost cycle. The sound power level has a drastic fluctuation when the liquid level of refrigerant in the gas–liquid separator is higher than the outlet of the evaporation tube during the defrost cycle. The reduction in noise is achieved by the redesigns that prevent the liquid level of refrigerant in the gas–liquid separator being higher than the outlet of the evaporation tube during the defrost cycle. Then, the noise level of original design and two redesigns was measured in a high precision semi-anechoicroom, respectively. The noise level of the refrigerator reduces from 30.2 dB(A) to 26.1 dB(A) and 24.4 dB(A) by increasing the volume of the gas–liquid separator for 87.1% and installing a ball valve respectively.