A sharp whistling noise may occur during the refrigerant throttling process in the electronic expansion valve of air conditioning systems

which may lead touncomfortable experiences. To reduce the whistling noise

the mechanism for the whistling noise and the noise generation rules as the refrigerant flows through the electronic expansion valve must be understood. In this study

an experimental rig was designed to adjust the refrigerant state before and after the electronic expansion valve and measure the generated whistling noise. The influences on the whistling noise of the refrigerant operation conditions and the valve opening width were measured. The results showed that the whistling noise came from the periodic oscillation of the fluid caused by the high-frequency pressure pulsation inside the valve. Its acoustic characteristics are the result of the selective amplification of the noise source signal near the resonance frequency of the Helmholtz resonance cavity structure comprising the annular conical throttle channel and the valve cavity. The sound pressure level of the whistle is mainly related to the refrigerant flow rate inside the valve and the valve opening width. The noise pressure level increased by 21% when the refrigerant velocity increased from 2.5 m/s to 3 m/s at a valve opening of 700 pls. The refrigerant flow rate inside the valve determined the fluid oscillation frequency

and the valve opening degree determined the resonance frequency of the acoustic cavity inside the valve. By changing the valve cavity structure to increase the resonance frequency

the oscillation frequency caused by the refrigerant impact inside the valve under common air conditioning conditions was lower than the resonance frequency

which can effectively avoid the generation of whistling noise.