Discussion Forum

Hi all,
I am modelling fluid flow through a microchannel using:

1. Weakly compressible Navier-Stokes
2. Convection and Conduction
3. Convection and Diffusion

I have included a docx with some images to help explain my problem more clearly. I want to investigate how heating the channel will improve mixing. I solve (1) and (2) to give a velocity field modified by the temperature gradient in the model. However, I am having problems solving (3).

I want to modify the diffusion coefficient in (3) according to the change in viscosity found in the first step. I can plot the temperature dependent viscosity by eta_chns, but how do I go about using this as a variable in my Convection/Diffusion model?

I am trying the following:

D(iostropic): ((D[m^2*s^-1])*(T)*(eta_in[Pa*s]))/((T_in[K])*(eta_chns(T[1/K])[Pa*s]))

D: initial diffusion coefficient value (I define this in constants)
T: variable from (2)Convection/Conduction
eta_in: initial viscosity value (I define this in constants)
eta_chns: variation in viscosity found by solving (1) and (2)...I cannot get this expression to work.

I can not figure out if I need to define a global expression, equation or function.
Your help would be much appreciated.
Regards,
Kevin