Abstract
Oil-injection improves twin-screw compressor performance significantly and its overall effect depends on the working fluid mass flow rate, the shaft speed, the injection position and the injected oil temperature. However, the individual contribution of each of these variables to the machine performance is yet not fully researched. Therefore, tests have been carried out on an air compressor with a male rotor diameter of 98mm, with injection nozzle sizes of 2, 3 and 4mm and with a nozzle of multiple holes. Tests were carried out with discharge pressures of 6.5, 8.5, 10.5 and 12.5 bar and rotor shaft speeds of 3000, 4000 and 5000 RPM. The results from the tests were compared with performance estimates at the same operating conditions as measurements against the standard injection nozzle of 5mm diameter. It was found that there is an optimum quantity of oil injected to obtain the best performance.
Highlights
The effect of oil injection on screw compressor performance is dependent on the compressor tip speed, the injected fluid mass flow rate, temperature, viscosity, and the fineness of its atomisation and the position of the oil injection port
In this paper, the performance of an oil-injected twin screw compressor is studied by varying the oil flow rate by changing the main nozzle diameters
The experimental study is conducted for discharge pressures from 6.5 bar to 12.5 bar and male rotor shaft speed from 3000 RPM to 5000 RPM
Summary
The effect of oil injection on screw compressor performance is dependent on the compressor tip speed, the injected fluid mass flow rate, temperature, viscosity, and the fineness of its atomisation and the position of the oil injection port. The cooling effectiveness was introduced as a factor in a thermodynamic model, and by this means it was shown that raising the oil flow by 10% lowered the specific power by 0.2% and raising the cooling effectiveness by 10 points lowered the specific power by 0.05% These results were not confirmed with experimental data. In order to gain a better understanding of the effects of oil injection on specific power over a range of operating conditions, the authors carried out tests on an oil-injected air compressor of 98mm male rotor diameter using oil injection nozzles of 2mm, 3mm and 4mm diameter at discharge pressures of, 6.5 bar, 8.5 bar, 10.5 bar and 12.5 bar and male rotor rotational speeds of 3000 RPM, 4000 RPM, and 5000 RPM. The test results obtained were normalised with the existing design nozzle of 5 mm diameter and compared, in order to gain a better understanding of the significance of each variable nozzle
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