# Diffusion Initial and boundary Conditions

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 October 30, 2015, 15:16 Diffusion Initial and boundary Conditions #1 New Member   Xuekun Lu Join Date: Oct 2015 Posts: 20 Rep Power: 9 Hi all, I am trying to modelling the permeability of a multi-channel pipe. I am struggling to define the reasonable initial and boundary conditions. I want to simulate this process: Diffuse H2 (hydrogen) into a multi-channel which is originally filled by Argon gas. I want to see the concentration or Mass distribution at last. Question: (1) Instead of using a constant Pressure inlet, how can I set a certain H2 pressure at inlet at the beginning, and let the pressure decrease naturally with the diffusion process? It sounds like set a initial condition at the boundary. (2) In which case shall I use freestream boundary? Thanks a lot !

 November 2, 2015, 11:14 #2 New Member   Sarang Join Date: Oct 2015 Posts: 22 Rep Power: 9 You will have to solve the following equations for this problem 1. Continuity 2. Momentum 3. Species transport As far as boundary conditions at the inlet/INFLOW you will set the pressure and the concentration of the inlet mixture. This is where you will specify that your inlet is made up of 100% H2 Initial condition is for your fluid domain and you will specify 100% Argon. Depending on the code that you are using you will specify either mass or mole fractions. Initial conditions for pressure needs to be set as well. Since you are solving the species transport equation the bulk mixing and species diffusion (assuming you have the right diffusivity co-efficients) will be taken care of.