Study On Bubble Coalescence In Multi-phase Systems Involving Liquid Phase

Bubble coalescence plays a significant role in determining bubblesize distribution, gas holdup, interfacial area and bubble rise velocity,which governs the performance of many bubble columns and distillationtowers. It is the research hot point for studying bubble coalescencemechanism in the multi-phase flow and related fields. In this paper, Experiments were made in various pure liquids, and theeffects of electrolytes Potassium Chloride (KCl), Sodium Chloride (NaCl)and surfactant Dodecyl sulfuric acid sodium salt (SDS) were alsoinvestigated. Bubble coalescence time was detected with a new systemcombining the laser diffraction technology and (or) CCD iamge gatheringtechnology, which avoid excessive pictures for high-speed photographingmethod and optical/electric transfer setting for pure optical method. Some modifications were made to previous plane-film models andsymmetrical dimple-film models. A plane-film model considering onlythe inertial force was developed and its programme was solved. Thechanges of contact area and approach velocity during their rising andcontact process for bubbles with regular shapes of spherical orellipsoidalm were also studied.The changing velocities every time stepwere used as intertial boundary conditions for solving dimple models withfully mobile surfaces. More real surface deformations of larger bubble and gas-liquidinterface were simulated using VOF method. Based on the simulatedresults of volume of fluid (VOF) method, a new asymmetrical model forlarger bubbles was developed involving internal and external influences,through which the assumptions can be removed to some extent. In order totheoretically solve the mechanism equations throughout the wholer-direction, the initial liquid film shape or film thickness and radialvelocity were precisely measured from the displayed contours or plots inVOF simulated results. The experimental data in this paper and those of previous work wereused to verify various models. Compared results show that the moreconsideration of surface deformation and the coupling between theinternal and external flow fields, the more accurate the theoreticalpredicted values are. Effect of interfacial solid particles on bubble coalescence was alsoinvestigated. Ignoring capillary waves from oscilliation, the collision andtangential interactions of interfacial solid particles on bubble coalescencewere introduced to rising-touching process.