Positive-displacement compressors and, among them, sliding-vane machines are widely used in the compressed air sector. As in many other industrial fields, the efficient utilization of energy has become a major goal also in this sector. The aim of the present activity is the numerical modeling and the experimental testing of the positive thermal effect due to spraying the lubricating oil inside sliding-vane air compressors using pressure-swirl nozzles. The benefits of proper oil atomization in positive-displacement compressors have been documented already by a number of investigations (Singh and Bowman, 1986; Stosic et al., 1988; Fujiwara and Osada, 1995; Valenti et al., 2013; Cipollone et al. 2014). The novelty of this work resides in the extension of a previous model to describe more accurately the quantity and the diameter distribution of the droplets generated by the nozzles and, consequently, to predict more precisely the heat transfer occurring between the liquid and the gas phase within a compression chamber. The model is applied to a pre-commercial mid-size compressor that is equipped with a number of pressure-swirl nozzles. The numerical data are validated successfully against the measurements of the pressure as a function of the angular position. The results indicate that the specific energy of compression is appreciable reduced with respect to the case of an adiabatic process. The model is applied here to a sliding-vane compressor, but it is general in nature and can be promptly modified for another kind of machine. It may be used also for optimizing type, number and position of the nozzles in order to further improve the performances of air compressors
