TED-AJ03-318 RAISING SCREW COMPRESSOR EFFICIENCY BY OIL ATOMISATION
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概要
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Despite the relatively low compression temperature in an oil-injected screw compressor, an isothermal efficiency of only 65% can be obtained. This can partly be explained by the fact that the cooling realised by the oil is not good. The heat transfer between air and oil is ineffective, due to the short contact time and the small contact surface. In literature little information is available about the exact physics of the cooling process and the optimal ways to implement the oil injection. Injection mainly happens through one or several large holes drilled in the compressor casing. The oil mass flow rate and temperature are mainly based on experience of the constructors. Atomisation of the oil by injection nozzles could result in a better heat transfer and thus a better performance of the compressor. At the Ghent University research is focussed on this oil injection system. Two research lines are pursued to obtain better understanding of the cooling effect of oil atomisation in a screw compressor. A test rig was build to assess the performance of different types of atomisers. Atomisers varying from fine atomisation to coarse atomisation were tested. The geometry used in the test rig has a flow passage similar to the flow path inside the screw compressor, in which a fan introduces air. The flow conditions and temperatures in the test rig are similar to the conditions in a running screw compressor. 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. Lowering the oil temperature is not beneficial if only the nozzle is considered as the oil viscosity rapidly grows, and thus the droplets get bigger. 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. An oil-cooling effectiveness is defined. 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 and the point of injection only gives small gains. Furthermore it is shown that the 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.
- 一般社団法人日本機械学会の論文
著者
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Paepe Michel
Department Of Flow Heat And Combustion Mechanics Ghent University
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Mertens David
Department Of Flow Heat And Combustion Mechanics Ghent University
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BOGAERT Wouter
Department of Flow, Heat and Combustion Mechanics Ghent University
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Bogaert Wouter
Department Of Flow Heat And Combustion Mechanics Ghent University