Scrutinizing the sources of inefficiencies in the piston-cylinder clearance of an oil-free linear compressor

Abstract

The piston of linear compressors is subjected to low side loads and metal contact can be avoided by feeding high-pressure refrigerant gas from the discharge system into the piston-cylinder clearance. This paper reports a thorough study on the inefficiencies associated with leakage and viscous friction brought about by the transient compressible fluid flow in the piston-cylinder clearance of an oil-free linear compressor. The main objective is to understand the effect of design parameters, such as compressor speed, piston oscillation amplitude, pressure ratio and radial clearance, on the volumetric and isentropic efficiencies. The compressor efficiency was found to be mainly affected by the clearance and pressure ratio. A reduction of 2.5% in the volumetric efficiency and 4.2% in the isentropic efficiency, for instance, were predicted when the radial clearance was varied from 2.5 to 10.0 µm.