Study of flow fluctuation in the thermal bubble pump tube

Abstract

In the present work, we were interested in the study of the oscillatory phenomenon of ammonia-water two-phase flow inside the bubble pump of absorption-diffusion refrigerators. In fact, flow instability can reduce the efficiency of the bubble pump. The simulation of two-phase flow in the bubble pump is conducted by using the drift flow model. Balance equations of the drift flow model and their closure relationships, as well as the numerical method, were developed. The numerical resolution allowed defining the void fraction, the liquid and vapor velocities, the pressure, and the mixing enthalpy against time. The effect of heat flux received by the bubble pump is simulated in the transitional regime. Simulated results of the vapor, liquid, and mass velocities show a flow fluctuation at the beginning of the operation. The duration of the fluctuation increase from 6 s to 12 s by reducing the heat flux from 5 to 2 kW/m².The void fraction profile makes it possible to distinguish that the slug and churn regimes are those which dominate the pump’s operating regime for a heat flux of 2 and 3 kW/m². The pumping action is influenced by the heat flux. A maximum of 10 kW/m² value of heat flux is defined for an obtained minimum of the pumping action.