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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.

Transient higher-frequency flow-induced tones are often perceived following air-conditioning (A/C) compressor engagements in automotive refrigerant systems, especially the ones with Thermostatic Expansion Valve (TXV) controlled systems. In this paper, the mechanisms of the acoustic tones induced by turbulent flow and shear-layer-instability in A/C lines are presented. Some of the recommended countermeasures for the attenuation and suppression of these flow-induced transient tones are also discussed.