Prediction and suppression of whistling noise in electronic expansion valve.

Whistling noise is the most serious flowing noise in the indoor electronic expansion valve (EEV) of multi-split air conditioners, and it is caused by resonance between the refrigerant flowing at a specific speed and the EEV chamber with a particular opening. The key for avoiding this noise is to identify the noise-generating speed range for a given EEV opening and keep the refrigerant flow speed outside this range. The purpose of this study is to develop a predictive formula for the noise-generating speed range at a given EEV opening. The basic idea for developing the predictive formula is firstly to establish the functional relation between the whistling noise frequency and the refrigerant flow speed, and then to establish the functional relation between the whistling noise frequency range and the EEV opening, and lastly to combine these two relations to determine the noisegenerating speed range for a given EEV opening. The predicted lower and upper limits of the noise-generating speed range are validated through experiments on a typical EEV for room air-conditioners using R410A as refrigerant. It is shown that the deviations of these two limits between predicted results and experimental data are both within 0.02 m/s at various EEV openings, meaning that the accuracy of the developed predictive formula for the noise-generating speed range at a given EEV opening is acceptable in engineering applications.