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In the thermal expansion valve (TXV) refrigerant system, transient high-pitched whistle around 6.18 kHz is often perceived following air-conditioning (A/C) compressor engagements when driving at higher vehicle speed or during vehicle acceleration, especially when system equipped with the high-efficiency compressor or variable displacement compressor. The objectives of this paper are to conduct the noise source identification, investigate the key factors affecting the whistle excitation, and understand the mechanism of the whistle generation. The mechanism is hypothesized that the whistle is generated from the flow/acoustic excitation of the turbulent flow past the shallow cavity, reinforced by the acoustic/structural coupling between the tube structural and the transverse acoustic modes, and then transmitted to evaporator. To verify the mechanism, the transverse acoustic mode frequency is calculated and it is coincided to the one from measurement.

Refrigerant flow-induced gurgling noise is perceived in automotive refrigerant systems. In this study, the condition of the gurgling generation is investigated at the vehicle level and the fundamental root cause is identified as the two-phase refrigerant flow entering the TXV for system equipped with variable displacement compressors. By conducting literature reviews, the acoustic characteristics of the flow patterns and the parameters affecting the flow regimes in horizontal and vertical tubes are summarized. Then the gurgling mechanism is explained as the intermittent flow is developed at the evaporator inlet. In the end, the improved and feasible design for avoiding the intermittent flow (slug, plug or churn flow) or minimizing its formation is proposed and verified in refrigerant subsystem (RSS) level. Finally, the guidelines for the attenuation and suppression of the gurgle are provided.