Experimental Investigation On Sliding-vane Air Compressors based on The Intracooling Concept

Continuing ongoing research for compressor efficiency enhancement, the option to use the lube-oil as a coolant in a novel two-stage sliding-vane compressor is investigated. A novel technique is proposed, named intra-cooling,consisting of spray-cooling the compressed gas exiting the first compression stage and leaving the coolant in the flow entering the second compression stage. High-pressure lubricant oil injection allows to leverage lubricant, which is already present for lubrication and sealing purposes, as a thermal ballast with substantial thermal capacity, able to limit the temperature throughout the compression process. Intra-cooling, in contrast to the familiar inter-cooling, allows for lower overall system complexity and for the oil to be available at very high pressures, a condition that can be beneficial for the injection process optimization. An experimental campaign is conducted on two prototypes of different sizes: a small-scale and a high-scale sliding-vane compressor based on the intracooling concept, with particular focus on the intracooling duct, to assess the concept operability and potential. The aim of the tests is to investigate experimentally the intracooling duct in different conditions of lubricant injection. The prototypes are designed for a relatively low delivery pressure (0.7-1.0 MPa). The oil injection system is composed by pressure-swirl nozzles placed on the compression stages end-plates and along the intra-cooling duct, hence performing both radial and axial injection.