Comparison of thermodynamic efficiency between constant, dual and multiple lead rotors for an industrial air screw compressor

Abstract

The goal of the European Union funded project "MOTOR" (Multi-ObjecTive design Optimization of fluid eneRgy machines) is the optimisation of fluid energy machines by using isogeometric analysis. This paper deals with the optimisation of the geometry of screw compressors. Screw compressors are usually built using helical rotors with constant lead. However, variable rotor lead holds the promise of higher efficiency due to an optimised progression of chamber volume, clearance, and discharge areas. This is especially true for high pressure applications and for working fluids with low isentropic exponent. This paper describes the optimisation of a variable lead rotor pair for an industrial air screw compressor. The rotors are divided into a discrete number of segments of constant lead, named multiple lead. Using a high number of rotor segments allows a design that approaches a uniformly varying lead. Thermodynamic simulation of the machines is performed using multi-chamber simulation with the simulation tool "KaSim". The thermodynamic simulation is coupled with a Nelder Mead algorithm, which evaluates the efficiency of the machines and optimises the progression of rotor lead. The achievable efficiency of this optimised multiple lead machine is compared with constant and dual lead machine configurations. Results of this study show that the highest efficiency can be achieved by using dual lead rotors.