Numerical Simulation Of Liquid Lens Evaporation On Immiscible Liquid

The evaporation of the liquid lens on an immiscible liquid is widely used in many industrial and scientific fields,so it is crucial to accurately predict the energy conversion,species transport and time evolution of the liquid lens.During the evaporation,the internal thermocapillary flow,external natural convection,and interfacial evaporative cooling are coupled together and affect the evaporation characteristics greatly.In this thesis,the slow evaporation under evaporative cooling and the fast evaporation under coupled multiple physical fields are studied by theoretical analysis and numerical simulation respectively.The influences of major factors on evaporation are analyzed,including internal thermocapillary flow,external natural convection,evaporative cooling number,initial volume of lens,superheat of heating surface,tangential angle ratio,etc.,and the variations of temperature field,evaporation flux,evaporation rate and evaporation life of lens is obtained.In this thesis,the internal evaporation rate,temperature field and external concentration field of the lens with only evaporative cooling effect are firstly derived through theoretical analysis,Then,the evaporation of the lens with the fully coupled physical fields is numerically simulated.It is found that the evaporative cooling can always inhibit the liquid lens evaporation,while the thermocapillary flow and natural convection can enhance the liquid lens evaporation.The total evaporation rate is determined by the competence between the interfacial evaporative flux and upper surface of the liquid lens.With the increasing liquid lens volume,the total evaporation rate will generally increase for fast evaporation,while for slow evaporation that only with the evaporative cooling effect,the total evaporation rate may decrease at a low tangential angle ratio.The evaporation life of the lens decreases with the increase of tangential angle ratio and superheat of the heating surface.With external air heat conductionthe theoretical analysis is conducted for the external concentration field,the evaporation temperature fields inside and outside of the lens as well.Meanwhile,the numerical model is established.The evaporation rate of the lens is calculated under the different ratio of thermal conductivity of the gas to the lens,and the results show that the thermal conductivity of the external gas would inhibit the evaporation.The influence of the external thermal conductivity on the evaporation is quantitatively analyzed under different superheats and tangential angle ratios Numerical simulations are carried out for the liquid lens with liquid pool below the effect of the height and thermal conductivity of the liquid pool and the base superheat on the evaporation of the lens is simulated.The evaporation of the liquid lens follows the constant contact angle mode,the transient variation of volume satisfies the "2/3 law",independent of evaporative cooling,thermocapillary flow,and natural convection,and it is analogous to the sessile droplet evaporation in constant contact angle mode.These findings can provide guidance for the wide application of liquid lens evaporation.