Effect of impeller blade profile on the cryogenic two-phase turbo-expander performance

Being the core-block of air separation and liquefaction plants, turbo-expanders should definitely be responsible for the most part of refrigeration capacity for the whole cryogenic system. The feasibility and economy of the whole cryogenic equipment can be prompted by achieving two-phase flow state at the turbo-expander outlet. A reasonable design of 3-D impeller blade has an important significance on the thermodynamic performance of turbo-expanders. In this paper, the influences of impeller blade profile on spontaneous condensation flow and thermodynamic performance are investigated. The non-equilibrium spontaneous condensation process in the flow passage is simulated based on Euler/Euler two-fluid models. Classical nucleation theory with non-isothermal correction and Gyarmathy droplet growth model are used for the prediction of the liquid droplets formation and growth. The definition of three-dimensional blade surfaces are determined by relative length of expansion section (RBe) and curvature of diversion section (Cur). The effects of the RBe and Cur values on the flow characteristics and thermodynamic performance are analyzed, such as velocity, nucleation rate, flow losses and exit kinetic energy. Based on results of the analysis, some theoretical guidance on the design of impeller blade profile for cryogenic two-phase turbo-expanders is obtained.