Numerical Investigations Of Rising Bubbles With Heat And Mass Transfer Through A Vertical Channel By Level Set Method

As the computer science develops greatly, numerical simulation provides a powerful tool to study dynamics of bubbles. This paper presents numerical study of bubble's rising, heat and mass transfer in vertical channel with the help of level set method to capture the interface and SIMPLEC algorithm to solve hydrodynamic equations over control volume.First of all, single air bubble rising vertically driven by buoyancy is simulated in an isothermal system. Numerical results show that volume correction level set is capable to capture the interface exactly and conserve bubble's volume. The calculated Reynolds numbers coupled with bubble's shapes agree well with experimental results. And also the dynamic motions of a bubble rising in viscous liquid are described. In addition, influence of density and viscosity ratio on terminal velocity and bubble's shape is investigated. Numerical results real that terminal rising velocity is affected more by density ratio while shape of bubble is affected more by viscosity ratio as the two ratios are within 10. However, both terminal velocity and bubble's shape are affected little as the two ratios are over 100.Secondly, two bubbles rising side by side in viscous liquid are simulated and the interaction of them is described. The effects of Weber number on coalescence are studied for Reynolds number is 200. Coalescence occurs when the calculated Weber number is about 2. The rising velocity decreases rapidly before coalescence and increases quickly after coalescence. The final rising velocity when coalescence happens is large than that when coalescence doesn't happen. The two bubbles bounce more frequently as Weber number increase in the absence of coalescence.Thirdly, heat and mass transfer is simulated when a vapor bubble rising in uniform-superheated liquid. As the temperature gradient at the interface is discontinuous, this paper presents an approach to calculate temperature gradient of interface. Under the simulation condition of Re=40 and We=5, the mean Nusselt number is taken into consideration to illustrate growth rate of bubble's volume.Finally, based on the distance function of level set method, another correction method is proposed, in which empirical factor is not applied. So it can reach a higher theoretical level. The new correction method has comparatively good correction effects on conservation of bubble's volume, according to the simulation results of single bubble rising in quiescent liquid and a water droplet falling through air onto a free surface.