Density Relation for Hydrogen Mixing
 

Dear All, I am modelling hydrogen leak in enclosed spaces, hence there is mixing of the gas(H2) with air at the exit of the leak. The speed of the gas at the exit is 20m/s at 4bar pressure, 15degC. The question is considering the non-ideal and compressible nature of the gas leaking at such low speed, and the constant density of air, what is the appropriate density relation to use when defining the molecular properties of air? Is it constant density, multicomponent mix, Ideal f(T) or Ideal f(T,P)? Furthermore, if I'm using a trimcell mesh with about 500,000 cell prepared in pro-amm, is there any good setting for the URF and residual tolerances? I have been getting divergence since I refined the mesh. Please I need guide from some with experience in similar model. Thanks