: Numerical Prediction of Radiated Noise Level From Suction Accumulators of Rotary Compressors

Jay Kim Structural Dynamics Research Laboratory University of Cincinnati Cincinnati, OH 45221-0072 Since the suction accumulator is one of components with large surface area in rolling piston type rotary compressors, its contribution to the total radiated noise may be substantial. In this study, possible noise sources of the accumulator are discussed. The noise radiated from accumulators are predicted using threedimensional vibro-acoustic analysis. The finite element method (FEM) and the boundary element method (BEM) are basic tools used in vibro-acoustic analysis. Important dynamic and acoustic characteristics of an accumulator, such as natural frequencies of the shell and cavity, transmission loss and transfer function, are also estimated. Introduction The suction accumulator is one of the largest components in a rolling piston type rotary compressor. In an ordinary setup of a rotary compressor system, the accumulator is attached to the external surface of the compressor shell, as shown in Figure 1. Because the accumulator has a large surface area, its contribution to the total radiated noise may be substantial. Therefore, it is necessary to consider sound performance of accumulators in the rotary compressor design in order to reduce noise. Sound performance of an accumulator can be evaluated from the sound pressure level (SPL) of the radiated noise. In this work, it is shown that use vibro-acoustic analysis can be used to predict SPLs numerically. In addition to SPL, the analysis is used to predict other acoustic characteristics, such as the transmission loss, and transfer functions. An accumulator may influence the thermodynamic performance of a rotary compressor due to back pressure built in the compressor suction cavity. Using a compressor simulation program, the back pressure can be calculated if the four pole parameters of the accumulator cavity are available. While it is not discussed in this paper, the vibro-acoustic analysis procedures demonstrated in this paper can also be used to calculate the four pole parameters of the accumulator cavity [1, 2, 3]. Noise Sources Noise sources of the accumulator may be considered as follows: I. Gas pulsations. Because of the intermittent nature of the operation of the compressor, pulsating flows exist in the cavity. The pulsating pressure developed in the accumulator cavity causes the vibration of the accumulator shell. 2. Structural vibration. The compressor shell vibration caused by unbalanced dynamic forces and compression actions inside the compressor shell are transmitted to the accumulator through the clamp and the connecting pipe. 3. Evaporation of liguid refrigerant Under some operating conditions, a small portion of the refrigerant may return as liquid and evaporate in the accumulator cavity. The abrupt increase of the specific volume of gas related to this phenomenon may act as a noise source. 4. Gas flow. The complex gas flow in the accumulator cavity may generate aeroacoustic type noise. It should be noted that noise radiated from an accumulator is eventually due to the vibration of its shell no matter what the noise source is.