City Research Online

Abstract

Screw rotor profile impacts the overall performance of screw compressor to a large extent. Its improvement will directly impact the screw compressor efficiency and reduce the power consumption for unit flow of compressed gas under given conditions as well as manufacturing cost in comparison with a less efficient compressor; and thus reduce its environmental influence. In times where efforts to improve performance are taken at every level, it is only natural to take up research in the direction of improving rotor profiles for better energy efficiencies. Hence, this research is aimed at developing a new screw rotor profile in anticipation to improve the adiabatic efficiency of screw compressor while being equally or more manufacturable than existing well known profiles. A comprehensive literature review of the history and methods of rotor profiling along with their manufacturability aspect has been conducted. Based on this review, rack generated profiles comprising of analytical curves such as N-Profile seem to provide a strong basis for further improvements. Investigation into mathematical formalisms that can enable a wider search space for analytically represented curves on rack could pave the way to better rotor profiles. With better control and exploration of the profile curves, the best possible shape of profile for a given application can be designed. One such method from topology called ‘Path Homotopy’ which enables continuous morphing of one analytical curve into another is shown to be suitable and quite useful for designing more energy efficient rotor profiles. A mathematical basis to successfully use this idea in profiling has been developed and is used to design profiles having up to 2% better energy efficiency than the state of the art rotor profiles. The scope of this method adopted for profiling may have a wider reach into domain of shape optimization problems in mechanical engineering. The understanding of drag losses in screw machines was adopted to adjust profiles to have minimum drag losses. It is experimentally demonstrated to lead to substantial improvements in the overall energy efficiency of oil-injected screw compressors. The combined homotopy and drag minimizing profile generation results in 1.5-2.5% improvement in energy efficiency over benchmark N-Profile. Considering the maturity of the field of rotor profiling, improvement of this order on top of a good profile is quite significant. On the manufacturability aspect of profiles, methods from literature which quantify it in terms of relative tool wear across profiles have been modified to devise a scale which can be used to compare two profiles. Using this method, it is found that the new profile improvements in energy efficiency come at a minimal compromise in manufacturability. This method is not only useful to evaluate manufacturability of various profile designs but it can also be used to trigger fine tuning of certain features to strike a balance between efficiency and manufacturability.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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