Gas Path Sound Transmission in Spherically-Shaped Reciprocating Compressors: Theory and Experiment

Gas pulsations within the refrigerant gas cavity is one of the principal noise propagating paths in reciprocating compressors. This paper provide a physical insight to the relationship between the gas pulsations inside the cavity and noise radiation of reciprocating compressors. The refrigerant gas cavity of the test compressor is modeled as a space between concentric spherical shells and analyzed with modal expansion techniques. Gas pulsations within the cavity are mathematically represented as the forcing terms of the inhomogeneous wave equation in spherical coordinates. The pressure distribution inside the cavity is then estimated accordingly. Based on the orthogonality principles, the noise radiation patterns associated with the gas pulsations are predicted. Acoustic modal analysis, directivity test and running speed sensitivity test are conducted to identify the acoustic characteristics of cavity and to verify the analytical model. The experimental results are in good agreement with the prediction of the analytical model. Thus, the concentric, spherical shell model well describes the acoustic characteristics of cavity within the test compressor. This model can also be employed as a design tool to analyze the effects of system parameter variation on overall noise radiation.