Study on suction pressure loss near suction end and stagnant pressure rise in p-θ diagram of Twin-screw refrigeration compressor for chiller

Abstract

• A twin-screw refrigeration compressor is tested under different operating conditions. • Two phenomena of efficiency loss are analyzed and causes are founded. • A three-dimensional CFD model is established to further analyze these phenomena. • Some optimization to avoid these efficiency losses is proved to be effective. To improve the efficiency of the twin-screw refrigeration compressor, two pressure characteristics in the p-θ diagram, such as suction pressure loss near the suction end (SESPL) and stagnant pressure rise in the compression process (CPSPR), were investigated in this paper. A three-dimensional CFD model of a twin-screw refrigeration compressor for chillers was established to analyze the generating mechanism of these phenomena. The p-θ diagram and performance of the compressor were tested and compared under variable working conditions, to verify the simulation results. Analysis results showed that the SESPL is caused by the small flow area between the working volume and suction chamber, and the CPSPR is mainly caused by inflow and outflow in the closed cavity of the vapor injection port. On the basis, some improvement directions were put forward to avoid these efficiency losses, i.e. appropriately delaying the suction end angle and blocking the vapor injection port. Experimental results indicated that the volumetric efficiency and total efficiency both increased by about 2% under different condensing temperatures after delaying the suction end angle of the axial suction port by 18° and blocking the vapor injection port of the compressor.