Altering the volumetric expansion ratio of a Lysholm helical screw expander

This is an analysis of the effects of the volumetric expansion ratio on the operating of a Lysholm helical screw expander. Extensive testing of the University of California Lysholm engine with a 5.3 volumetric expansion ratio was performed. The expansion ratio was reduced from 5.3 to 4.0. Tests were performed at a variety of speeds and qualities for a 5.0 pressure ratio and at a variety of speeds and pressure ratios for 99 percent quality. It was predicted that decreasing the volumetric expansion ratio would decrease the leakage fraction and thereby increase efficiency. This occurred as predicted. Isentropic efficiency increased 20 percent for 50 percent quality steam and 16 percent for 33 percent quality steam, all for an inlet pressure of 120 psia and a speed of 9000 rpm. A maximum efficiency of 47.2 percent was reached at 33 percent quality, 9000 rpm and a pressure ratio of 5.0. The leakage rate did not appear to be a function of expansion ratio, was expected.