CFD Modeling of Two Phase Cryogenic Flow in an Internal Orifice

The study is concerning the modeling of cavitating cryogenic flows, present in many engineering applications as superconductivity technology, liquefied natural gas plants, aerospace components, and many other fields. In this paper we re-examine previously developed cavitation models, used for water liquid, to adapt that to the simulation of cryogenic fluids. Usually the cavitating flows are modeling with the basic hypothesis of isothermal flow, however it’s known, for cryogenic fluids, that there is a temperature decrease in the vapor cavity. Cryogenic fluids, in fact, are characterized by larger compressibility if compared with fluids, such as water, at room temperature, by a small difference in density between vapour and liquid phases and by a small latent heat of vaporization. The aim of this paper is a numerical investigation of this phenomenon, using a multiphase formulation that accounts for the energy balance, variable thermodynamic properties of the fluid and nucleation transport equation. The numerical analysis has been performed by the commercially available code Fluent release 6.3 and the Fluent beta version v.12.0. After the validation of two different cavitation models by comparison with experimental data present in literature, numerical simulations have been performed to analyze and better understand some experimental observations obtained by an experimental apparatus of University of Salento, where the two-phase cryogenic flow passing through an internal nozzle has been studied. Numerical cavitation patterns and pressure distribution, obtained by the mechanical equilibrium model, are found to agree very well with experimental data. In all cases the results show that as vapor fraction get larger, temperature becomes lower in liquid nitrogen. Vapor fraction increase corresponds to gas phase generation, therefore, latent heat should be absorbed from the fluid. As a result, temperature decreases as vapor fraction increases.