Numerical investigation of oil injection in screw compressors

Abstract

Oil injected screw compressors are commonly used in the industry. The position and amount of oil injection are determined experimentally or by heat balances with an assumption of uniform oil distribution in the compression chamber, which is not validated. This paper presents a study on the oil distribution within a screw compressor chamber using Computational Fluid Dynamics (CFD) with Volume of Fluid (VOF) multiphase model. Prerequisite for using CFD in screw compressors is a body fitted numerical mesh produced by software SCORG. The analysis was carried out on a newly designed screw compressor with a 4–5 lobe combination. It was found out that injecting the oil through two separate ports , one on each rotor, has advantages compared to the injection through a single port. The injection ports are conveniently positioned to ensure an even oil distribution within the compression chamber. If the same amount of oil is injected through the two separate ports instead of the originally designed single port , the maximum gas temperature within the chamber could be reduced by 30°–35 °C leading to reduction in specific power by 1.8%. Techniques used in this study can improve the performance and efficiency of a wide range of screw compressors.