Contribution of modern rotor profiles to energy efficiency of screw compressors

Abstract

Screw rotors are the heart of screw compressors. And the energy efficiency of industrial machines is a matter of tremendous significance now more than ever. Historically, rotor profile developments have played a key role in making screw compressors energy efficient and commercially viable. Further attention to manufacturing aspects of rotor profiles and the invention of the rack generated rotor profiles led to rotor profiles having good manufacturability. The principles of rotor profile generation and manufacturing are available in open literature since 1960’s. But more and more literature on rotor profiling has been published since then. Modern screw rotor profiles (patented close to and in the 21st century) have all the principles of a good profile incorporated in their design. Hence the industry and profile designers at large are aware of the increasing difficulty to further make the twin screw compressor rotor profiles more energy efficient. This paper tries to quantify the contribution of rotor profile to energy efficiency of a typical twin screw compressor by comparing the most recent (hence modern) screw compressor rotor profiles. In order to fairly compare different rotor profiles, all are retrofitted to a single size, lobe combination, rotor length, and helix angle. Only the curves constituting the profile, as dictated in the patent documents of the respective profiles, have been changed. Tools such as SCORPATH and SCORG have been used to do the geometric and thermodynamic calculations on the profiles. Keeping the working conditions same for all the retrofitted but different profiles, a comparison has been made. This comparison sheds some light on how much is the energy efficiency of a particular twin screw compressor influenced by a mere change of profile. This analysis can be further extended to establish reasonable targets for twin screw compressor manufacturers to improve energy efficiency of their machines via improving their rotor profiles. This remains the future scope of this work.