On the contribution of magnetic forces to the overall noise of reciprocating compressors

Regulations concerning the noise emission of home appliances have become stricter in recent years and this is pushing manufacturers to improve their vibroacoustic characteristics. In this regard, the reciprocating compressor, which is one of the main sources of noise and vibration in these appliances, is drawing particular attention and thus it has been investigated by many research groups aiming to reduce its vibratory energy and the noise emitted. While the compressor is operating, different mechanisms generate vibratory energy. Some of these have been extensively studied and their contribution to the overall noise is well understood. However, one of the noise and vibration sources in this type of equipment that has not been studied in depth is the electric motor. Until now, the majority of researchers dealing with the vibroacoustic problem of reciprocating compressors have considered the electric motor only as a transmission path of vibratory energy. The objective of this study was to model not only the structural behavior of the electric motor but also include the electromagnetic phenomena in order to ascertain the magnetic forces that are acting on the stator. Once these forces are obtained and validated, their influence on the overall noise of the compressor can be assessed. The finite element method was used to model both the electromagnetic and structural system. The results indicated that the magnetic forces contribute at some specific frequencies when the compression loads are considered. In cases without the load, due to the gas compression, it was observed that the magnetic excitations have a notable influence, within a wide frequency range, on the overall noise.