Experimental and numerical investigation of lubrication system for reciprocating compressor

Abstract

Sufficient lubrication of the moving parts in a variable capacity inverter compressor is vital since it can directly affect the performance and expected lifetime. In this study, the lubrication system of a compact inverter compressor (CIC) is numerically and experimentally investigated. In the numerical modeling, a finite volume-based algorithm is used to model two-phase (air–oil) flow inside the compressor using Volume of Fluid Method (VoF) method. Transient behavior of the oil flow under laminar flow conditions is both simulated by imposing Sliding Mesh (SM) and the Moving Reference Frame (MRF) methods at various crankshaft speeds varying between 1200 and 4500 rpm. The measurements are taken using an experimental setup to compare/validate CFD results obtained from SM and MRF methods. Flow visualizations are performed with a high-speed camera to determine the oil climbing and required time for sufficient lubrication precisely. Moreover, the acceleration of the crankshaft is determined via high-speed camera and employed as a user-defined function to model the start-up period of the compressor. It is shown that with increasing crankshaft speeds, the average oil mass flow rate released from the upper part of the crankshaft is increasing almost linearly. It is also shown numerically that with increasing oil viscosity, the mass flow rate decreases. The comparison of experimental and CFD results reveals that the MRF solutions are in a better agreement with the measurements up to 2800 rpm. The SM method became favorable as a CFD method due to better agreement with measurements between 3000 and 4500 rpm.