# boundary mass flux in kg/m^2/s

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 September 15, 2022, 13:17 boundary mass flux in kg/m^2/s #1 New Member   Yusef Join Date: Aug 2022 Posts: 5 Rep Power: 2 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.

 September 16, 2022, 14:39 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,071 Rep Power: 60 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.

 September 17, 2022, 08:52 #3 New Member   Yusef Join Date: Aug 2022 Posts: 5 Rep Power: 2 Thank you for your reply. The mass flux I want to impose is negative. Therefore, mass flow inlet is not an option.

 September 18, 2022, 11:07 #4 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,071 Rep Power: 60 You can specify a negative mass flux and a negative velocity therefore mas flow inlet and velocity inlet are options.

 September 18, 2022, 14:19 #5 New Member   Yusef Join Date: Aug 2022 Posts: 5 Rep Power: 2 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.

 September 18, 2022, 17:33 #6 Senior Member   Lorenzo Galieti Join Date: Mar 2018 Posts: 303 Rep Power: 10 If you define the total mass flux and the correct molar fraction, then you impose also the flux of the species.

 September 19, 2022, 07:49 #7 New Member   Yusef Join Date: Aug 2022 Posts: 5 Rep Power: 2 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.