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Numerical analysis of oil injection in twin-screw compressors

Basha, N. (2021). Numerical analysis of oil injection in twin-screw compressors. (Unpublished Doctoral thesis, City, University of London)


Compressors are widely used in the manufacturing, process, construction, and energy industries. They consume nearly 20% of the electricity generated worldwide [1]. Nearly 66% of this electricity comes from burning fossil fuel that greatly impacts the environment. Improving compressor efficiency by even a small percentage will considerably reduce electricity and energy consumption. This thesis focuses on improvement in the efficiency of oil-injected compressors. The injection of oil in the working chamber of a screw compressor increases volumetric efficiency and reliability, but it increases power losses. Also, the oil needs to be separated from the gas, which requires additional equipment and energy losses, not to mention the contamination of the environment with the oil carryover. The injected oil has a significant influence on compressor performance and the environment.

The distribution of oil injected in a compression chamber is critical for performance and reliability. Accordingly, investigations are carried out using Computational Fluid Dynamics (CFD), based on a Volume of Fluid (VOF) model, to determine the oil distribution. The predictions were compared with test results. This was applied to an industrial compressor with a traditional single oil injection point. Using different nozzle diameters allowed the evaluation of the oil and temperature distribution close to rotor surfaces to be determined. It was found out that the high gas temperatures coincided with the regions of low oil concentration. With increasing the oil flow rate through a single port, the cooling of these hot spots was not achieved beyond a certain point unless the second oil-injection port was introduced on the opposite rotor. The injection through ports on both rotors reduced the compressor chamber temperature by 30°-35°C and the specific power by 1.8%. Furthermore, the adaptive mesh refinement technique in a simplified compression domain was used to simulate the film formation and disintegration. The disintegration has shown various oil phase breakup levels due to interfacial shear, inertial, and centrifugal forces, leading to ligaments, lobes, and droplets.

This study shows that computational methods could be exploited for improving compressor energy consumption through oil distribution. One such way is the enhancement of oil distribution to cool high temperature spots. Another is understanding the oil phase breakup due to the forces acting in a compression chamber that can affect the oil droplet sizes and cooling surface area. Techniques used in this research can be applied to improve efficiency for a wide range of screw compressors.

Publication Type: Thesis (Doctoral)
Subjects: T Technology
Departments: Doctoral Theses
School of Science & Technology > School of Science & Technology Doctoral Theses
School of Science & Technology
Text - Accepted Version
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