Advanced Polytropic Calculation Method of Centrifugal Compressor

The contribution deals with a new method for calculation of the polytropic change of real gas or gaseous mixture. This method can be used for high accurate polytropic analysis of centrifugal compressors compressing real gases. In the course of design and test evaluation of the compressor the most important is to decrease energy consumption. Advantage of the polytropic analysis is the fact that the polytropic change is very close to the actual process which is in progress in the centrifugal compressor. Several various methods for calculation of polytropic process have been developed till now. The new method is based on numerical solution of basic definition equation of polytropic change in form edH = Vdp where “polytropic efficiency” e has constant value along the whole polytropic path. This method enables to calculate arbitrary unknown parameters from set of quantities (polytropic efficiency, initial pressure and temperature and final pressure and temperature) if the remaining parameters and gas composition are known. Suitable real gas equation of state can be used to calculation of real gas thermodynamic properties. Presented method is independent of equation of state. Accuracy of this method depends only on chosen equation of state. Computer procedure based on above mentioned method can be incorporated into computer programs for calculation of compressors, refrigerating cycles, expansion turbines, gas or steam turbines etc.