NUMERICAL ANALYSIS OF THE TRANSIENT COMPRESSIBLE FLUID FLOW IN THE PISTON-CYLINDER CLEARANCE OF AN OIL-FREE LINEAR COMPRESSOR

摘要

Oil-free linear compressors adopt aerostatic bearings to avoid metal contact between the piston and cylinder.Despite the small friction in the bearing, the gas flow in the piston-cylinder clearance can generate losses thatdecrease the compressor efficiency. The present paper reports a model developed to evaluate such losses and theireffects on the volumetric and isentropic efficiencies. The transient compressible fluid flow in the gap is simulatedwith a commercial code based on the finite volume method, whereas the compression cycle in the cylinder issolved with an in-house code using a lumped model formulation. The model was employed to assess thecompressor performance as a function of four parameters: compressor speed, piston oscillation amplitude, pressureratio and radial clearance, It was found that the compressor efficiency is mainly reduced when the clearancedimension and pressure ratio are increased.