CFD Simulations Of Marangoni Effect

During mass and transfer process,the surface flow induced by surface tension is commonly known as Marangoni effect.Marangoni effect can accelerate renewal of the interface and promote the percolation of solute to the bulk phase,thus it has a significant impact on mass transfer process.The complex induction and development process of Marangoni effect is hardly well understood simply through experimental technique and theoretical methods.Therefore in this work Marangoni effect occuring at the interface during gas-liquid mass transfer process is investigated in several aspects numerically by means of the CFD technique.Firstly,investigation on artificially provoked Marangoni convection at a gas-liquid interface was conducted.It was found that the surface flow mainly spread along the interface and there existed double vortex beside the injection point.The maximum surface velocity appeared 3mm distant from the injection point.The surface velocity curves can be divided into three stages:accelerative stage,uniform stage and decelerating stage.The mass transfer coefficient increased after injection concentration.It increased more quickly in the low concentration area and more slowly in the high concentration area.Secondly,Marangoni effect induced at the gas-liquid interface during volatilization process was investigated numerically.The simulation results showed that thermal effect caused by acetone-heptane volatilization process could also induced Marangoni convection,which enhanced the mass transfer coefficient obviously.The study on ether-heptane mass transfer process indicated that Marangoni convection induced by concentration gradient was weaker than that induced by temperature gradient and had a weaker influence on strengthening mass transfer.On the basis of investigation on planar interface,Marangoni convection induced in two different kinds of curved interface,which is droplet and vapor bubble interface,was studied.The effect of diameter on mass transfer process accompanied by Marangoni convection was further investigated.As for the vapor bubble,the average concentration of the vapor bubble increased faster with the smaller diameter.It led to rapid reduce of interface mass flux and later induction of Marangoni effect.Meanwhile,weaken mass transfer process resulted in weaken Marangoni convection.Concerning the droplet,when the droplet was smaller,Marangoni effect was induced earlier.But after developing inward over a period of time,Marangoni convection extending inward became harder because of limited space of smaller droplet and it turned out that the average concentration of the interface and interface mass flux decreased rapidly.Finally,study on Marangoni instability was carried on.The mass transfer process was disturbed by a small-amplitude random perturbation and it caused Marangoni convection.With the perturbation intensity increasing,Marangoni convection was induced earlier and the maximum surface velocity was lower in the induction stage of Marangoni convection.When the convection was stable,there was almost no difference in the surface velocity and concentration among different perturbation conditions.The increase of the dimensionless Ma number led to earlier induction of Marangoni convection,higher surface velocity and smaller interface concentration.