[Yong666]

Dear all, I would like to impose a boundary mass flux in unit of kg/m^2/s in fluent. On the boundary, there are options to impose a species mass flux or mass fraction with values from 0 to1. This is obvious not applicable in my case. I also saw some suggestions to impose source term in the cells adjacent to the boundary. But the source term is in unit of kg/m^3/s. In fact, according the governing equation, the divergence of the boundary flux is the source term. I'm struggling to figure it out. Can anyone give me some suggestions or guidance? Thanks.

[LuckyTran]

You're looking for a mass flow inlet or a velocity inlet. Use the mass flux option for a mass flow inlet. A velocity unit having units of velocity m/s + a prescribed inlet pressure and temperature which you must always provide will also effectively yield a mass flow since the area of the boundary is a constant. The difference between a mass flow inlet and velocity inlet is, for a mass flow inlet you prescribe inlet stagnation properties. At a velocity inlet, you prescribe static properties.

[Yong666]

Thank you for your reply. The mass flux I want to impose is negative. Therefore, mass flow inlet is not an option.

[LuckyTran]

You can specify a negative mass flux and a negative velocity therefore mas flow inlet and velocity inlet are options.

[Yong666]

Yes, you are right. But my case involves multispecies. I want to define a mass flux for a specific species on the boundary. I have defined a species mass fraction on the boundaryas as a function of the mass flux. Thank you anyway for your reply.

[LoGaL]

If you define the total mass flux and the correct molar fraction, then you impose also the flux of the species.

[Yong666]

Thank you for your reply. I'm aming to solve the evaporation induced concentration polarization problem. The mass fraction is unknown and is what I want to solve. The good thing is I can correlate the evaporative flux to the concentration gradient in the solution.