| The research on the heat and mass transfer characteristics of liquid droplets has always been a hot topic in basic research and engineering applications.However,most of the previous studies focused on single component droplets,while in the actual industrial process,the composition of droplets is more complex.The heat and mass transfer process of multi-component droplets is complicated and uncertain due to the difference of their internal components,especially for micro and nano scale research is more difficult.In this paper,starting from the simplest multicomponent droplet binary droplet,using water-n-octane as the working fluid,the stability of binary droplet in suspension was first verified,and then through the construction of different hydrophobic and hydrophilic oil walls,the dynamic process of binary droplet spreading with different internal phase content was explored,and the influence of different internal phase content and different wall characteristics on droplet spreading was analyzed.Finally,based on droplet spreading morphology,the droplet model was simplified,and the dynamic behavior of droplet evaporation under different wall superheat was studied.The influence of spreading morphology difference on droplet evaporation process was explored,and the evaporation characteristics of binary droplet were revealed.In the verification part of the stability of binary droplets,it was verified that droplets with internal phase contents of 5%,10%,15% and 20% could stably exist in the suspension.Then,the dynamic spreading of the four internal phase contents on the wall surfaces with different characteristics and the final spreading results were discussed.All the droplets with internal phase content on the hydrophilic and hydrophilic oil wall surface and the droplets with lower internal phase content on the hydrophilic and hydrophilic oil wall surface will have oil-water separation phenomenon.The droplet with higher internal phase content on the hydrophobic and hydrophilic oil wall will appear the spreading pattern under the oil,which is attributed to the competition relationship between the oil-water interaction and the copper-water interaction.For both hydrophilic and hydrophobic wall surfaces,oil-water adhesion appears.The difference is that demulsification occurs at the top of the droplet in the former,while on the wall surface in the latter.What is more special is that the droplets with low internal phase content do not demulsify in the spreading of the hydrophobic and oil-phobic wall surface,but stably deposit on the wall surface,forming the spreading pattern of oil inside and water outside.This is because the interaction between the oil phase and the wall in the droplet with low internal phase content is weak,so the spreading morphology of the droplet will not be changed.To sum up,the droplet spreading morphology of water-n-octane binary components can be divided into four types:oil-water separation,oil-water adhesion,oil-inside water-outside,and oil-under water.Based on the above spreading morphology,the characteristics of droplet evaporation under different wall superheat was studied in this paper.For droplet evaporation at low superheat(500K),the internal heat transfer effect of droplet A is the best,followed by droplet B and droplet C,which is attributed to the difference in thermal resistance of different droplet forms during heat transfer.Under the condition of high superheat(800K),all droplet shapes would boil rapidly.The difference is that the existence of oil phase near the wall in droplet shape C would make it boil rapidly in a very short time.In particular,due to the existence of oil phase inside the droplet of form B,its evaporation forms will differ under different superheat conditions,that is,under the condition of medium superheat(600K,700K),microexplosion will occur,and the occurrence of microexplosion mainly depends on whether the temperature of oil phase inside the droplet of form B reaches Ledenfrostpoint. |
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