Numerical analysis of gas bearings in oil-free linear compressors

Abstract

Recently, linear compressor technology has gained increased attention in vapor compression systems due to its compactness and lower frictional losses compared with the conventional reciprocating compressors. Since the absence of the crank-mechanism eliminates the rotation and reduces the side loads on the piston centered inside the cylinder, it is possible to operate the linear compressors without oil lubrication. A number of advantages can be obtained in terms of the refrigerant compatibility, operation conditions and the system cost. In order to enable oil-free operation, while minimizing frictional losses and leakage flow between the piston and the cylinder wall, a gas bearing approach is applied. Little work was found in the open literature related to the numerical analysis of gas bearings coupled with a comprehensive dynamic linear compressor model. This paper presents a 1-D gas bearing model based on a Finite Volume Method (FVM) applied to a linear compressor. The dynamic characteristics of the gas bearings on the gas film pressure field are analyzed using the model. When integrated together with a comprehensive dynamic linear compressor model, it is possible to predict leakage and frictional losses within the compressor as well as the overall performance.