Traditional compressor design methods make it very difficult to make significant improvements to screw compressors required for refrigeration and air conditioning applications. The principles which determine the optimum design of such machines are reviewed and, in some cases, redefined. These include rotor profiling, configuration and proportions, clearance distribution and bearing clearances and it is shown that there are conflicting requirements for them when attempting to obtain optimum performance. The best result can thus only be obtained by consideration of all the relevant parameters in an optimisation procedure, which leads to rotor designs that vary according to the specific duty of a machine, rather than follow a standard pattern An outline description is given of a process modelling procedure which has been developed to optimise the design of a compressor by the use of multi variable minimisation methods that take simultaneous account of all these parameters As a result of a collaborative project between industry and an academic institution, this procedure was applied to the design of a new refrigeration screw compressor, which was then built and tested. Its performance was then compared with that of the machine it was intended to replace. It is shown that the optimised design was up to 9% better than the original machine.

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