Discussion Forum

I am trying to run a simulation for a sessile droplet evaporating in air due to pure diffusion. Here are some details to brief you about the model. 1) I have selected the material/mesh (identical) co-ordinate system for the deformed geometry and want to map the system in the spatial co-ordinates so I have selected the same for it. 2) Using the laminar interface for both liquid-gas domain, I have given free deformation condition to both domains and zero displacement at the boundaries. The fluid-fluid interface is selected and applied at the interface in which the mass flux is given by mf.(Described in below points). 3) Transport of dilutes species (tds) is only applied in the gas domain, the liquid-gas interface has been given the saturated concentration defined by the interpolation function because of its dependency on temperature. The outer walls of gas domain is given ambient concentration at 20degC, the same is given as initial value in air domain as variable because it changes due to diffusion from the droplet. 4) The predefined domain mass flux is used as variable mf which is given by: mf = (tds.dflux_cxnx+tds.dfluxny)M_w where, nx,ny are normal components and M_w is molecular mass of water (for consistent units). 5) Heat transfer in fluids is used because as there is diffusion so the droplet will cool down, this is done by giving the boundary heat source at liquid-gas interface as: -H_vapmf where H_vap is latent heat of vaporization. 6) Couplings are mass flux -> mesh velocity in laminar flow, mass flux -> heat transfer in fluids, heat transfer in fluids -> saturated concentration (tds).

Problems: 1) Is the formulation of problem correct ? Am I using the correct equation for the mass flux from comsol itself? 2) I did not find any equation for the surface tension dependency on temperature. 3) When I run the problem it runs without any error but the mesh does not move, it has the same mesh for all the time steps which is wrong. Please help me find the issue so that I can run the model.