IOR - Improving cooling and oil distribution in an oil-injected screw compressor

3rd February 2022 4:00 pm

Compressors today consume around 20% of the electricity generated worldwide and contribute to megatons of CO2 . Thus, even minor improvement of their efficiency will substantially impact sustainability. Oil-injected twin-screw compressors are widely used in industry for gas compression because of their high volumetric efficiency and reliability. The injected oil has a significant influence on the performance of these compressors, and its overall effect depends on the working fluid mass flow rate, the shaft speed, injection position and injected oil temperature. However, the individual contribution of each of these variables to the machine performance is yet not thoroughly researched.

Previous experimental and numerical studies have shown that the mass flow of oil and oil droplet sizes when varied have a significant effect on compressor performance. However, the distribution of oil in the compression chamber that is capable of affecting performance is not researched. Therefore, in this research, a novel design methodology, a stable, reliable, and accurate two-phase CFD model is developed by writing User Defined Nodal Displacement code in a parallel framework.

This model is applied to visualise oil distribution on rotor surfaces for a varying oil-injection flow rate in a typical twin-screw compressor. The model has predicted performance very close to experimental data and indicated high-temperature spots due to lack of oil in the compression chamber. Based on this observation, improved oil-injection design is suggested and implemented to limit high-temperature spots and thereby to improve compressor specific power. Applying this novel design methodology researchers and designers in the sector will be able to improve compressor efficiency and deliver a sustainable design solution. Further, the physics accounted by the model is extended with Adaptive Mesh Refinement techniques which will prevent failures due to oil lubrication in operation. This visualisation of the unstable oil regime provides deeper insight into the dynamics of the injected oil in a compressor. This thesis demonstrates that there will be at least 1.8% improvement in compressor specific power which will in turn have a huge positive impact for the environment and costs.

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