电子膨胀阀内啸叫噪声特性及发声规律的实验研究

空调系统中电子膨胀阀节流时出现的尖锐啸叫噪声严重影响用户使用舒适性，了解制冷剂流经电子膨胀阀时的啸叫噪声产生机理及其发声规律是解决上述噪声问题的关键。本文设计了可以对阀前后制冷剂状态进行调节控制并对产生的啸叫噪声进行测量分析的实验系统，得到不同工况及阀开度下的啸叫噪声发声规律。研究表明：啸叫噪声来源于阀内流体高频压力脉动引起的流体周期性振荡，其发声特性是阀内环锥形节流通道与阀腔构成的亥姆霍兹共振腔结构对共振频率附近的噪声源信号选择性放大的结果。啸叫噪声声压级主要与阀内制冷剂流速及阀开度有关，阀开度为700 pls下制冷剂速度由2.5 m/s增至3 m/s时，噪声声压级提高了21%；阀内制冷剂流速决定了流体振荡频率，阀开度决定了阀内声腔共振频率；通过改变阀腔结构以增大共振频率，使常见空调工况下阀内制冷剂冲击引起的振荡频率低于共振频率，可以有效避免啸叫噪声产生。

Whistling Noise Characteristics and Noise Generation Rules of Electronic Expansion Valve

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.