Numerical Study On The Profile And Conjugate Heat Transfer Characteristics Of Evaporative Thin Liquid Film Of Binary Fluids

The heat and mass transfer characteristics of the evaporative thin liquid film near the three-phase contact line are widely used in life and industrial production such as evaporation and boiling,covering the theory of fluid mechanics,mass transfer and heat transfer.The mechanism of such phenomena with multi-component working fluids on the surface of the solid substrate is more complicated.At present,there is no theory to fully reveal the profile and evaporation mechanism of thin liquid film.The effects of binary liquids,surface tension characteristics and thermal properties of solid substrates on conjugate heat transfer in thin liquid film are seldom discussed.Based on Young-Laplace equation and dynamic theory,a numerical and conjugate heat transfer model of flow and evaporation in thin liquid film region is established.The profile of thin liquid film and heat and mass transfer characteristics are solved by using MATLAB iteration algorithm,and the thin film region is identified.The influence of working fluid,superheat,ambient temperature and thermal capillary on the profile,heat and mass transfer characteristics of thin liquid film are investigated.The results show that the thin liquid film length of binary alcohol solution is longer and the heat transfer performance is better than that of pure water.Superheat has an important effect on the profile and heat transfer characteristics of thin liquid film.With the increasing of slperheat,the thickness of thin liquid film increases and the length of thin liquid film decreases.The evaporation and heat transfer characteristics of the thin liquid film region are enhanced,but the contribution of the thin liquid film region to the overall heat transfer of the whole liquid film decreases.Due to the special surface tension characteristics of n-butanol solution,the effects of thermal capillary on the profile of binary working thin liquid film is different at various ambient temperattres.A two-dimensional con.jugate heat transfer model is established to study the evaporation of droplet sessile on solid surfaces,which contains evaporative thin liquid film region,intrinsic meniscus region,solid substrate region,gas region and gas-liqLiid,liquid-solid,gas-solid interface.The effects of relative thickness and therlnal properties of solid substrates,as well as hydrophilic and hydrophobic on heat transfer characteristics are investigated by FLUENT with UDF.The results show that there is a small temperature valley of' solid substrate near the three-phase contact line,and the more prosperous the evaporation,the larger the temperature valley is.The length of the thin liquid film increases with reducing the thermal conductivity of the solid substrate or increasing the thickness.But the evaporation mass flux in the thin liquid film area is reduced.While the wettabilitv of the solid surface is better,heat and mass transfer characteristic of thin liquid film is larger.For the hydrophobic surface,there is a counter-clockwise eddy current in the gas region.The evaporated liquid molecules return to the sas-liquid interface under the effect of the air side eddy current,thus the evaporation of the thin liquid film region and even the whole droplet is inhibited.