Influence Of Plate Wettability On Population Balance Of Droplets In A Pulsed Disc And Doughnut Column

The pulsed disc and doughnut column(PDDC)is an important liquid-liq uid extraction equipment in the nuclear chemical industry.To further study the liquid-liq uid two phase flow in PDDC is of great significant in its performance prediction,design and operation.The population balance model(PBM)is one of the most used method to solve problems involved with droplets in the liquid-liquid two phase flow at present.Nevertheless,it's still hard to describe the droplets behaviors in PDDC based on the reported research for the PBM.On the one hand,most sub-models of the PBM are based on theoretical derivation and reverse derivation using the data of droplet size distribut io n,which is lack of direct experimental data for the sub-models of the PBM.On the other hand,the effect of plate wettability on droplets behaviors has never been included in the PBM to the best of our knowledge.Thus,we will study the law of droplets behaviors in liquid-liquid two phase flow,and directly measure the sub-models of the PBM in PDDC with the help of high-speed microscopic camera technology.Firstly,we deduced a seven-source-term PBM based on the traditional four-sourceterm PBM,and developed the expressions of new source terms through defining three new sub-models for the PBM.Secondly,we studied the droplets behaviors in PDDC with three kinds of plates with different wettability to the dispersed phase in a water-kerosene system.In the experime nt,we had observed 9 types of topology transforming modes for the dispersed phase in the PDDC,including tensile breakup,popping breakup,revolving breakup,and droplets colliding onto the plate,partially coalescing into the liquid layer and generating a residual droplet,totally coalescing into the liquid layer with no residual droplet,and dropping dispersion,jetting dispersion,dragging dispersion.Then we further investigated the law of droplets breakup,coalescence and dispersion,and analyzed their mechanis ms detailedly.This work is the first time to describe the droplet coalescence and dispersion phenomena including the influence of plate wettability in PDDC.Finally,the data of droplet number density distribution,breakup frequency functio n,coalescence frequency function and dispersion frequency function based on the sevensource-term PBM were counted in this experiment.Furthermore,empirical correlations were established for these sub-models,and a simplified flow model was combined with the population balance equation to calculate the droplet number density in the PDDC.The predicted results agree well with the experimental data,which proved the reliability of the correlations and the feasibility of the deduced seven-source-term PBM.