KR419: How can we model forced diffusion in binary mixtures (single phase)? (Solution ID: 672)
ANALYSIS J = J_ordinary + J_forced J1_ordinary = -rho D12 Grad yi J1_forced = -rho^2 * w1 * w2 * y1 * y2 * D12 * (F1 - F2) / (P * W * W) where w1 = mol wt 1 w2 = mol wt 2 y1 = mass fract 1 y2 = 1-y1 W = mol wt mixture F1 = Force Vector on species 1 (N/kg) F2 = Force Vector on species 2 (N/kg) P = pressure This is solved by UDF species equation source is equal to S = - DIV (J1_forced) Problem is solved using UDS: UDS(0) = y1 UDS(1) = xcomp of J1_forced UDS(2) = y-comp of J1_forced UDS(3) = z-comp of J1_forced In Define Adjust function, we * compute J_forced. * compute grad of components of J_forced (nine terms stored in memory)( * add appropriate components to get divergence: div J = d(J1x)/dx + D(J1y)/dy + d(J1z)/dz Source term = Div J is stored in UDM(0) For boundary condition, at a wall: J.n = 0 J = J_ord + J_forced, thus Flux(1) = J1_ord . n = - J_forced . n Where J1_forced is evaluated at the wall So far only wall boundary conditions are in the UDF. Others can be added as necessary. |
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