Simulation of a two-phase flow through a DeLaval Nozzle

International audienceA two-phase impulse turbine used to replace the classic expander in a refrigeration cycle needs a nozzle/expander to transform the flow enthalpy into kinetic energy. Replacing a classic isenthalpic expansion with isentropic one, increases the cooling capacity by up to 20% for the same compressor input power and generates an additional electric power. During this transformation, the static pressure of the flow decreases and a phase change occurs at the nozzle inlet. The mechanics of an expanding and flashing flow in the convergent and divergent parts of the nozzle is studied analytically and then simulated using the CFD software Fluent13. A separate evaporation model is added to the fluid dynamics algorithms in Fluent13 in order to create the phase change inside the nozzle. The evaporation model is based on the classical theory of nucleation and on experimental results: it calculates the heterogeneous nucleation initiated by the wall cavities and the heterogeneous nucleation initiated by the presence of vapor bubbles in the flow. The accuracy of the Fluent13 model is verified by comparing its results to experimental results with the same boundary conditions and nozzle geometry