Cooling of oil injected screw compressors by oil atomisation

Abstract

This paper addresses the effect of oil atomisation in an oil-injected screw compressor. A test rig was built to assess the performance of different types of atomisers. Atomisers varying from fine atomisation to coarse atomisation were tested. Experiments on the test rig show that lowering the oil droplet diameter results in a considerably higher heat transfer. Growing oil flow rate, also gives a better cooling effectiveness. In parallel with the experiments, a thermodynamic model is developed by which the compression process can be calculated for every degree of revolution of the male-rotor. This way the influence of cooling oil temperature, cooling oil mass flow rate and injection point can be analysed. Having a better heat transfer effectiveness does not give a considerable gain in specific work. Lowering oil temperature gives better results, while changing the oil flow rate only gives small gains. Furthermore it is shown that cooling oil coming from the bearings has a negative influence on the performance. This paper shows that trying to reach isothermal compression through oil atomisation is not possible. The importance of the cooling effectiveness in the thermodynamic process is too small to have a significant influence.