Experimental study of a retrofitted scroll compressor for operation with two-phase refrigerant flows

Abstract

The present paper introduces an experimental investigation of a scroll compressor working with two-phase refrigerant flows, in the frame of a novel thermodynamic cycle making use of two-phase compressions/expansions called REGEN-BY-2.

The design of the test bench dedicated to two-phase compression will first be explained. The objective of this test bench is to assess the performances of the compressor working with a two-phase refrigerant-oil mixture under varying conditions such as inlet pressures, inlet vapor qualities, oil circulation ratios, pressure ratios and speeds. Three experimental campaigns have been conducted, the first two are dedicated to compare different oils, while the third does not use any oil, thereby experimenting a pure-refrigerant two-phase compression. The methodology to obtain the compressor inlet vapor quality is detailed, and the related assumptions developed. The performance indicators, i.e., isentropic and volumetric efficiencies, are defined for a two-phase oil-refrigerant mixture. A total of 253 operating points (with and without oil) have been used to generate 3D maps, showing the evolution of the efficiencies for varying pressure ratios and inlet qualities. The results shows a decrease of efficiency at low vapor qualities, especially at high pressure ratios, where under-compression is amplified. Finally, the results of the pure-refrigerant compression are analyzed, showing decent isentropic efficiencies, with a minimum of 50% at a vapor quality of 0.35 and an optimal pressure ratio of 2.7.