CFD parametric investigation for two-phase flow of ammonia-water mixing in bubble pump tube

Abstract

Two-dimensional numerical simulation of two-phase ammonia/water flowing under uniformly heated tube is used. ANSYS Fluent is used to predict the time evolution of thermal and hydrodynamic parameters of the bubble pump. Phase-dependent turbulent models are used to calculate the turbulent viscosity of each phase. Through User-Defined Functions, different interfacial force models and the wall boiling model are implemented in the code. The simulation results show a slow oscillation of hydrodynamic parameters such as pressure, mass flux, vapour velocity and liquid velocity during the initial stage of operation; however, a vigorous oscillation is detected for the temperature behaviour. The amplitude and period of oscillation decrease with the heat input increasing. By using the void fraction contour, it is possible to predict the flow regime along the bubble pump at different times of the operation. The domination of flow regime is the function of heat flux too. It is bubbly to slug for heat fluxes less than 5kW/m2 and transits from churn to annular for 15 and 50kW/m2 of heat flux.