Numerical study of the flow in a two-phase nozzle for trilateral flash cycle applications

Abstract

A two-phase nozzle is a critical component in organic flash systems, and its design and operation must be carefully considered to handle the complex two-phase flow of the working fluid and achieve system performance. This study deals with the use of computational fluid dynamics (CFD) to assess the performance of a converging–diverging nozzle in a trilateral flash cycle (TFC) system. Simulations have been performed using available cavitation models and the turbulence closure is achieved using the Realizable k-ε model. In particular, the flow features in terms of the generated thrust, the pressure distribution, velocity, and void fraction within the two-phase nozzle have been calculated with isopentane as the working medium for inlet temperatures of 50 °C and 60 °C. Two cavitation models, namely the Schnerr and Sauer model and the Zwart-Gerber-Belamri have been selected and their results have been compared to experimental measurements from the literature. It is observed that the thrust force improves as the working fluid inlet temperature rises. Results in terms of the static pressure, velocity, and void fraction are consistent with the physics of flashing flows in two-phase nozzles. Indeed, the static pressure and velocity remain almost constant after the throat. Furthermore, the flow leaving the nozzle is predominately vaporized. The numerical model could be used to perform a parametric study to examine the effect of various parameters, such as nozzle geometry, inlet conditions, and thermodynamic properties of the working fluid, on the nozzle performance and identify the optimal operating conditions.