Multi-bubble Coalescence Simulations with Large Density Ratio Using Improved Lattice Boltzmann Method

This paper simulates the bubble motion characteristics by lattice Boltzmann method in a bubble pump lifting pipe of a lithium bromide absorption refrigeration system. The density ratio of lithium bromide solution to water vapor is as high as 2778. An excessively high density ratio may cause numerical instability in the gas–liquid interface during the simulation processes. In this paper, an improved lattice Boltzmann model (ILBM) is used to solve the velocity fields and the pressure fields to simulate the multi-bubble motions in the lifting pipe. The ILBM is constructed by using a single distribution function to solve the velocity fields and the pressure fields based on free energy model with large density ratio. The simulation results include the coalescence processes, pressure distributions, and velocity distributions of bubbles. In order to investigate the effect of multi-bubble coalescence on the temperature distribution of the flow field, the improved lattice Boltzmann model is also coupled with thermal model. The results show that bubble coalescence is greatly affected by the disturbance of the surrounding flow field and the shape of the bubble is distorted and varies in various forms. In the point of multi-bubble coalescence, the velocity increases, and the pressure and temperature decrease.