How does MassFraction(species=’species’) work?

    • zdfrankman


      I am trying to simulate a microfluidic channel (50um x 1.5cm) with a low pressure differential (3.6Pa causing 7.5e-5m/s max flow). At the bottom of this channel, there are supposed to be cells that consume the 6.88e-8 mass fraction inlet oxygen, with the exit of the channel then producing 2.08e-8 mass fraction oxygen. 

      To experiment with this, I have downloaded ANSYS Fluent 2021b and input a wall boundary condition of 0 species mass fraction, causing wall diffusion. In this instance, I see near-immediate diffusion of oxygen out of the channel.

      I then input MassFraction(species='o2') as the wall mass fraction, with the thought that this would result in zero diffusive flux. After all, if the wall has the same concentration as the cell adjacent the wall, there is no differential, and therefore no diffusive flux.

      However, I find that there is an identical species flux as the 0 wall mass fraction. This indicates to me that the function MassFraction(species='species') is returning 0 at all positions along the wall, despite the Mass Fraction of oxygen being above zero.

      What am I doing wrong?

    • Rob
      Ansys Employee

      What is the value assigned to the expression? I think you've assigned the value to the cell of the value of the cell, which isn't going to work. 

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