Experimental investigation of internal leakages and effects of lubricating oil on the performance of a four-intersecting-vane rotary expander

Abstract

In this paper, a four-intersecting-vane-rotary expander prototype is presented, and the performance was measured experimentally in dynamic and static conditions. The mechanism is different from conventional rotary vane machines because it has a non-circular stator with radius of between 35.7 and 40.7 mm. The prototype was designed to be eventually implemented in a refrigeration system. However, for testing compressed air was used as the working fluid. The expander was tested at rotational speeds of up to 1750 rpm, suction pressures up to 5 bar(g) and a discharge pressure of 0 bar(g). The effect of different operating parameters and lubricating oil grades on the expander was experimentally studied under dynamic conditions. Then, the internal leakage characteristics of the prototype was analyzed under static conditions. The maximum volumetric and isentropic efficiencies measured were 31.2 % and 45.6 %, respectively. Generally, higher speed and a more viscous oil improved the volumetric efficiency. The expander's isentropic efficiency was significantly affected by the suction pressure, viscosity of oil and rotational speed. The static leakage test showed that the prototype's housing was properly sealed. The average contributions of internal leakages through the radial clearance, vane tips, rotor slot and end face gaps were 37.2 %, 33.3 %, 16.2 % and 14.1 %, respectively. It was observed that the internal leakage paths were generally independent of each other.