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June 20, 2018, 23:45 |
Constant mass flow rate boundary condition
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Senior Member
Seyyed Ali H.M.
Join Date: Nov 2009
Location: Utah
Posts: 107
Rep Power: 17 |
Hi everyone,
I am trying to make a boundary condition for my solver that keeps the mass flow rate constant (I need to mention that it's solving diffusion of gas in porous medium). I cannot assume k and gradient of P as constant or uniform as they change over the boundary condition. The method I'm trying to do for this boundary condition is to assume a small volume before the boundary condition, and set a pressure that changes over time (similar to what happens in the experiment). The pressure variation is calculated as: dP/dt * (V/RT) = m ̇_(bc )−m ̇_r V is the volume of the boundary condition space (it's tubing in my experiment), R is gas constant, T is temperature of the gas, is the desired flow rate defined in the boundary condition, is the flow rate at the boundary that is calculated as: m ̇= ∫ −k/μ ∇P.(P/RT) dA Now the problem is that gets bigger than and that will reduce the boundary condition pressure. This causes the simulation to blow up if P becomes negative. I have to make dt very small for this to work, or I have to define this boundary condition as implicit. Can you guys tell me how to make it implicit? Something like: (P^(n+1)−P^n) / Δt = RT/V (m ̇_(bc) − m ̇_r^ (n+1) ) If you have any suggestion for any other method to define this boundary condition, I would like to hear it.
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SAHM Last edited by sahm; June 20, 2018 at 23:50. Reason: didn't show the equations. |
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