Thermodynamic properties of oil droplets in oil-injected screw compressors and their influencing factors

As a typical positive displacement compressor, screw compressors are widely used in various industrial fields with a fast-growing trend, especially with the boost of the application of oil injection technology. The oil injection process inside the screw compressor is complicated and difficult to be captured by direct observation experiment, so is the accompanying heat transfer process. On the basis of single particle dynamics, the Lagrangian method is used to establish a spatial kinematic model of oil droplets in the simplified chamber of an oil-injected screw compressor, the droplet trajectory is analyzed. The relationship between the oil droplet diameter, injection velocity and temperature and the free flight time of oil droplets in the compression chamber is obtained. In order to investigate the liquid-gas two-phase flow after oil injection, the Level Set Method is adopted to simulate the oil distribution in the compression chamber. The impacting process of oil droplet on a hot wall is simulated, the influence of oil injection parameters such as the injection speed, temperature difference, droplet diameter, and the initial velocity on the heat transfer between oil droplets and hot gas and the wall is analyzed theoretically. For the simulated cases studied, the oil droplet diameter has the greatest effect on the gas-liquid heat transfer, while the temperature difference plays a greater role in the heat transfer between the oil droplet and the hot wall than other factors. The research in this paper helps to further understand and accurately predict the heat transfer process in oil-injected screw compressors, which is important for improving the energy efficiency of screw compressor.