I am a new user of CFX. I consider gaseous flow in a 2D microchannel (L=3mm, H =0.0012mm).In this problem I want to use slip boundary conditions:

(1) Ug-Uw = Kn*(delU/deln)

(2) Tg-Tw = (Kn/Pr)*(delT/deln)

where Ug = vel of gas, Uw = vel of wall, Kn = Knudsen number(for slip flow 0.001 < Kn <0.1), n = inward normal direction to the wall, so (delU /deln) and (delT/deln) are the tangential velocity and temperature, Pr = Prandtl number. Are these possible to write using CEL function? But in CEL how (delU/deln) can be written? If not possible then how can I write using FORTRAN subroutine? Please give me directions or give me any sample subroutine that I can write my subroutine. If any one help me I will be grateful to him and appreciate his kindness.

Yours Truly Sohag

Dear Opaque and Robin, Both of you are so expert and always try to response to others problems.Would you plz see my problem that I send and give me some instructions that will help me. Yours Truly Sohag