Author(s)

Y. Y. Yan & Y. Q. Zu

Abstract

Both bubble coalescence and droplet separation are important physical phenomena in the natural world and a variety of process industries. This paper presents results of numerical simulation of behaviours of bubble coalescence and droplet separation. The velocity distribution functions of two particles are used in lattice Boltzmann equations. Based on the lattice Boltzmann method (LBM), both the phenomena of two rising bubbles coalescing in liquid and a liquid droplet break-up on wetting boundaries are simulated. Typically, such two-phase problems of large ratio of liquid–gas densities up to 1000 are studied. Keywords: bubble coalescence, droplet separation, numerical modelling, lattice Boltzmann method. 1 Introduction Both bubble coalescence and droplet separation are important physical phenomena in the natural world and a variety of process industries. It is a common occurrence in two phase flow and flow boiling that the evolution of bubbly flow to slug and annular flows accompanies processes of bubble coalescences. The coalescence or separation of droplets are also popular in droplet and film cooling condensations under difference surface conditions. Numerical modelling of bubble coalescence or droplet separation has been attempted by researchers for many years. Conventional CFD methods based on solving Navier-stokes equations can simulate free surface flow and bubble shape evolution with time [1-3] but can not effectively simulate problems of bubbles or droplets coalescences. Although the phenomena of bubble coalescences have been simulated by VOF method in [4] but only a two dimensional problem was discussed and the ratio of gas-liquid densities was also limited.

Keywords

bubble coalescence, droplet separation, numerical modelling, lattice Boltzmann method.