Self-Excitation Mechanism of Reed Valve in Refrigerant Compressors

This study presents a basic idea for the self·excitation mechanism of reed valves in refrigerant compressors used for air conditioners or refrigera· tors. The detailed experimental data on the phase lag of fluid pressure, which were obtained from a forced vibration test on a simple axisymmetrical model, namely a resonator, composed of the valve, the valve plate, the cylinder and the piston, were presented, first. Secondly, the Helmholtz resonance fre· quency for the resonator with flow was empirically determined from the experimental data on pressure phase-lag, and therewith the end correction factor in calculating the Helmholtz resonance frequency was calculated backwards, thus figuring out the contraction of flow in the discharge port. Conclusively, the possibility of dynamic behavior of the contraction of flow in the discharge port was suggested, and thus the basic self-excitation mechanism of reed valves was clarified. INTRODUCTION From a basic standpoint that the self-excitation mechanism of reed valves in refrigerant compressors used for air conditioners or refrigerators should be, first of all, clearly identified, a forced vibration test on a simple axisymmetrical model, namely a resonator, composed of the valve, the valve plate, the cylinder and the piston was performed in the previous study [1]: the valve was exposed to compressed gas flow and forced to vibrate in the frequency range from 50 to 500 Hz, and the fluid pressure was measured to reveal its frequency characteristics and spatial distribution in amplitude and phase lag relative to the valve vibration; the similar measurement was performed for various cylinder volumes. As a result, first, a dynamic stability criterion for self-excited vibration of the reed valve was presented, where the forced vibration frequency was divided by the Helmholtz resonance frequency to reduce it to a nondimensional form. In the previous study, furthermore, the validity of its dynamic stability criterion was ensured by performing a free vibration test on the reed valve, and in addition, the vibration frequency of reed valve in flow, which is significantly higher than its natural frequency in still air, and the significant works of the fluid force inducing self-excited Vibration also, were carefully examined. However, a basic self-excitation mechanism of the reed valve has not been still addressed at all. · Among theoretical studies especially on the vibrations of the reed valve controlling the refrigerant gas flow from the discharge port, there has been a study by Trella [2], in which the mutual interaction between the compressed refrigerant gas flow and the valve vibration is treated: the flow region was divided into 4 sections, and the continuity equa· tion and the momentum equation were applied to each flow section, thus deriving basic