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Investigation of Mechanical Losses in Oil-flooded, Twin-screw Air Compressors

Abdan, S. (2023). Investigation of Mechanical Losses in Oil-flooded, Twin-screw Air Compressors. (Unpublished Doctoral thesis, City, University of London)


Approximately 15-20% of the world's generated electrical power is consumed by compressors where rotary oil-lubricated compressors account for nearly 60% of the entire air compressor market. According to market research, the demand for those of the twin-screw type is likely to increase at a Compound Annual Growth Rate (CAGR) of 5% from 2021 to 2026. Thus, even minor improvements in their efficiency can lead to a substantial reduction in carbon footprint.

With the increasing demand for more energy-efficient machines, one of the ideas in the screw compressor for optimising their performance is to focus on reducing power loss. To do this, the elements contributing to the power loss and their quantification need to be understood. Analytical procedures for the design and performance estimation of twin screw compressors are well-developed and widely available, but the determination of power loss, in oil-flooded machines is only approximated.

This study focuses on finding the elements of power loss arising from the oil-injected, twin-rotor screw compressor and quantifying the contribution of individual elements' power loss for different compressor sizes. The approach is to find available technologies and develop new methods for the prediction of power loss in elements like rolling element bearings, shaft seals, oil drag and transmission.

After a comparison of available methods bearing power loss prediction and literature available experimental results, the Harris model fits best for the prediction of power loss arising from rolling element bearing. Based on the semi-analytical approach and experimental measurement presented by Frölich et al. (2014) and Engelke (2011), respectively, a combined model is developed for the prediction of power loss from the shaft seals. As the oil in the compressor experiences inertial and pressure-induced flow, a combined Couette-Poiseuille flow model is established for drag loss estimation. This drag loss model is experimentally validated with different screw rotor profile configurations. It is understood from the predictions for total power loss and its comparison for different sizes of the compressor, that the bearing power loss and oil drag loss are the main contributing elements to the total power loss whereas shaft seal power loss is negligible.

With the use of the proposed method and parametric analysis, the elements contributing to power loss and the effect of different operational parameters like pressure ratio, speed and size of the compressor are analysed. This can help the designers to optimise the working of the compressor at the design stage.

Publication Type: Thesis (Doctoral)
Subjects: Q Science > QA Mathematics > QA75 Electronic computers. Computer science
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Science & Technology > Computer Science
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
[thumbnail of Abdan Thesis 2023 PDF-A.pdf]
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