Tests of a two-stage, axial-flow, two-phase turbine

A two-phase-flow turbine with two stages of axial-flow impulse rotors was tested with three different working-fluid mixtures at a shaft power of 30 kW. The turbine efficiency was 0.55 with nitrogen-and-water of 0.02 quality and 94 m/s velocity, 0.57 with Refrigerant 22 of 0.27 quality and 123 m/s velocity, and 0.30 with steam-and-water of 0.27 quality and 457 m/s velocity. The efficiencies with nitrogen-and-water and Refrigerant 22 were 86% of theoretical. At that fraction of theoretical, the efficiencies of optimized two-phase turbines would be in the low 60% range with organic working fluids and in the mid 50% range with steam-and-water. The recommended turbine design is a two-stage axial-flow impulse turbine followed by a rotary separator for discharge of separate liquid and gas streams and recovery of liquid pressure.