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/m? and transits from churn to annular for 15 and 50kW/m? of heat
flux.