HI~ I have some problems about mixing of two fluids.

1)I have two B.Cs(Inlet) in "scalar boundaries".One is fluid(1) and set the "concentration" to zero and another is fluid(2) and set to 0.3 . 0.3 is the mass fraction of fluid(2) in fluid(1) in mixing problem for me. Is the setting right or wrong??

2) what is the "fixed concentration" and "flux"??

thanks for any help offered thanks!!

Wrong - the 0.3 is a volume fraction, not mass fraction. If you want to use a mass fraction, you have to do the conversion yourself.

'Fixed concentration' (this is on wall boundaries, right?) is where you specify the actual scalar concemtration value (or temperature in the case of heat transfer). 'Flux' is where you specify the actual flow rate of the scalar (in or out), or heat flux in the case of heat transfer.