Molecular Dynamics Simulation Of The Evaporation Process Of A Sessile Argon Droplet

The evaporation of sessile droplets is a common natural phenomenon and attracts more and more attentions because of many applications in technology and biology.For example,inkjet printing,pesticide evaporation,spray cooling and the “coffee ring” etc.The evaporation of sessile droplets is complicated and changeable.The wetting property of substrates influences the evaporation greatly.Meanwhile,there is a Kapitza resistance at the solid-liquid interface which hinders the heat transfer from the substrate to the droplet.Studying the heat transfer process in the adsorbed layer near the solid wall is very important for understanding the energy transfer mechanism of droplet evaporation.Thus,this paper presents a series of molecular dynamics simulations on the evaporation process of a droplet on heated substrates,and will mainly discuss the influence of initial system temperature and solid-liquid energy parameter on the evaporation.The aim will focus on energy transport through the solid-liquid interface by analyzing the proportion of local heat flux along the perpendicular and parallel directions with the solid-liquid interface.The main works and results are as follows:Firstly,the evaporation of sessile droplet with a vacuum atmosphere was discussed.Some of the liquid particles left the droplet to the vapor phase because of the pressure difference,and the droplet gradually evaporated to a steady state.During the steady state,the mass-density decreased sharply through the liquid-vapor interface and increased at the solid-liquid interface.Meanwhile,there was an absorbed layer at the vapor-solid interface.In addition,the influence of initial system temperature and potential well parameter on the contact angle were studied.It was easily seen that the contact angle gradually decreases with the increase of initial temperature and the potential parameter.What's more,the substrate was heated when the droplet was in the steady state to study the accelerated evaporation.It was found that the evaporation processes of a pure sessile droplet is usually divided three stages:(1)The contact radius is constant meanwhile contact angle reduces;(2)The contact angle is constant while contact radius reduces;(3)Both the contact radius and contact angle reduce until the droplet disappears finally.Meanwhile,in the accelerated evaporation process,there is a thermal resistance at the solid-liquid interface,which hinders the heat transfer from the substrate to the droplet.In the adsorbed layer,most of the heat is transferred along the tangential direction of the solid-liquid interface,and only a small amount of heat is transferred from the substrate directly to the inside of the droplet along the vertical direction.In the end,the influence of initials system temperature and potential well parameter on the accelerated evaporation was studied.When the initial system temperature was increased,the evaporating time was decreased,partly because the contact area of solid and droplet was increased which enhanced the heat transfer between the substrate and droplet.Meanwhile,for the hydrophilic substrates,the Kapitza resistance decreased with the increase of contact angle which enhanced the heat transfer,too.For the other hand,the evaporating time decreased when the solid-liquid energy parameter was increased.Because the contact area of solid and droplet was increased which enhanced the heat transfer between the substrate and droplet.Meanwhile,for the hydrophilic substrates,the Kapitza resistance decreased with the increase of solid-liquid energy parameter which enhanced the heat transfer,too.