Numerical Simulation On Hydrodynamic Characteristics Of Sessile Droplet And Meniscus Evaporation Using Arbitrary Lagrangian-eulerian Formulation

In the numerical simulation of droplet and meniscus evaporation, howto track the free interface precisely and timely is quite a problem. Theinterface-capturing methods, such as Volume of fluid method (VOF) orlevel-set (LS) method based on Eulerian formulation, cannot calculate theflow and force at the free interface accurately; the interface-trackingmethods based on Lagrangian formulation cannot deal with bigdeformation problem and the calculation is inefficient and difficult. A fullycoupled transient numerical model of droplet and meniscus evaporationusing Arbitrary Lagrangian–Eulerian(ALE) formulation is developed inpresent research for the first time. The merits of Lagrangian formulationand Eulerian formulation are combined in ALE: not only it can track thefree interface and therefore calculate the interface flow and forceaccurately, but also its applicability in big deformation problem isextended and calculation efficiency is improved.Results of droplet evaporation simulation show that evaporativecooling should be taken into consideration in predicting the evaporationrate, or the evaporation rate will be overestimated. The initial contact angle,thermal conductivity of the substrate and the Marangoni flow haveinfluence on the time required to get into quasi quasi-steady-state.it willtake more time for a droplet with big contact angle on a poor thermalconductivity substrate. Marangoni flow accelerates this process. The acceleration is more obvious in the cases with big contact angles and goodconductivity substrates.the temperature distribution is homogenized andthe evaporation is enhanced by Marangoni flow. If other conditions are thesame, the flow direction is determined by the initial contact angle. Theflow direction will be clockwise when the contact angle is smaller than10°,while it will be anticlockwise when the contact angle is larger than15°.When the contact angle is between10°and15°the clockwise flow andanticlockwise flow will be coexist.Results of meniscus evaporation simulation show that if thetemperature rises or the heat flux increases, the contact line will decline,the contact angle will enlarge and the curvature of the interface willincrease to achieve a new balance. It is because the evaporation is mostintensive in the contact line nearby, so the differential pressure between thevapor side and liquid side increase, in addition the surface tensiondecreases as the temperature or heat flux increases.