Mixing questions

Peter

hi all, im fairly new to the world of cfd and i have a few questions. it would be great if you could help me out, im not having much luck with the help files in cfx.

my project is to model microfluid mixing, ie. fluids mixing on a very small scale. i have setup a mixer and the fluid i am using is a Variable composition mixture of water and ethanol. is this the right fluid type to be using? i want to model the flow with ethanol flowing in one inlet and water in the other, but i cant really figure out how to do this. i have to constrain water as the basic fluid and then input the ethanol through one inlet, i am finding that the fluids are mixing straight away, much faster than possible, and then the ethanol seems to dissapear downstream. does anyone have any experience with this kind of problem? thanks very much all, peter