Numerical Simulations of Bubble Pumps

A bubble pump is a key component for diffusion-absorption refrigeration systems operating at a single pressure. Nevertheless, research focusing on bubble pumps is not widely found in the literature. In this study, a bubble pump model with a shape of vertical tube subjected to a uniform heat flux from the tube outer surface is numerically simulated. A saturated ammonia-water solution enters the bubble pump inlet and receives heat from the pump wall along the entire pump length. During the process, most of the ammonia in the solution vaporizes, and the remaining solution is lifted by the buoyant force created by the ammonia vapor. A numerical model was implemented by employing a commercial CFD code. The applicability of the numerical model implemented in the code to the present numerical simulations was validated through a comparative study referring to experimental data of a boiling phase change flow of water in a vertical pipe being subjected to a uniform heat flux. To investigate the influence of the bubble pump’s geometrical dimension and the heat input on the operating status and performance, numerical simulations were performed for four bubble pumps with different diameters subjected to five amounts of heat flux. Simulation results are provided in terms of the flow parameters including void fraction, and vapor and liquid velocities. The simulated spatial distributions of the flow parameters were found to have steep gradients in the radial direction near the pump wall due to the heating from the pump wall. In addition, simulated flow parameters were compared to those in previous one-dimensional (1-D) work for the same problem. It was found that the void fraction profiles along the pump length simulated in this study seem to be similar to those in 1-D models, but somewhat different quantitatively. Based on the results, the present numerical simulation model of the bubble pump is considered to be useful for certain industrial applications.