Performance Analysis of Oil-Injected Screw Compressors and its Applications

A computer model for performance analysis of rotary screw compressors was introduced in a previous paper by the authors(!). In this paper, experimentally obtained flow and heat transfer characteristics are used in the performance simulation. Heat transfer coefficient is determined from experimental relation between the volumetric efficiency and the inlet temperature. Flow coefficients are obtained from the · efficiency-clearance curves. Applying those coefficients to the performance simulation, good agreements are obtained between testec:l and calculatec:l performance for three c:lifferent prototype compressors. A new rotor profile aimec:l at higher performance is c:lesigned basec:l on the simulation results. The testec:l performance of the new profile compressor is much higher than that of a conventional compressor, as prec:licted by the simulation. The new profile compressor has been applied to a commercial series of packaged screw compressors. INTRODUCTION Computer simulation appears to be a sui table tool for analysis of screw compressor processes and useful in c:letermining the optimum rotor shape which is one of the requirements of high performance. In recent years, many studies have been pursued in simulating compressor performance for both oil-free type anc:l oil-injectec:l type. Fujiwara et al. (1) previously presented a computer moc:leling for an oil-injectec:l screw compressor, in which the effects of oil on the gas leakage and cooling were considered. Some flow and heat transfer characteristics are required for the computer simulation, which were empirically assumed in the previous paper. However, these characteristics directly affect the accuracy of the performance prediction. Therefore, correct evaluations of these characteristics are essential in the accurate prediction performance. Heat transfer between gas and oil is especially important. In a suction process, gas is warmed by high temperature oil and consequently, the compressor performance goes down. On the other hand, gas temperature rises in the comp~ession and discharge proce':'aes and the gas is generally cooled by the injected oil, thus reduclng power consumption. Singh and Bowman (2) analyzed the movement of oil droplets in a working space and calculated the heat transfer between gas and oiL Stosic et al. (3) also used an oil droplets model and studied the influence of the droplet size on the working process. From a mo~e practical point of view, the authors triec:l, in this paper, to determine flow and heat tranfer coefficients using experimental pe~formance data.