CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Main CFD Forum (http://www.cfd-online.com/Forums/main/)
-   -   Implement constant heat flux boundary condition (http://www.cfd-online.com/Forums/main/99565-implement-constant-heat-flux-boundary-condition.html)

new_at_this April 6, 2012 11:09

Implement constant heat flux boundary condition
 
I have written a matlab code that will solve for the developing temperature field given a velocity field. At the moment I have already implemented the constant wall temperature boundary condition and the results look correct.

Now I am trying to implement the constant heat flux boundary condition. I have the equation below
q'' = -k \frac{\partial T}{\partial n} = -k \frac{T_1-T_w}{\Delta y}

where T_1 is the first interior point and T_w is the wall temperature.

I convert to non dimensional temp
\theta = \frac{T - T_e}{q''\frac{H}{K}} and calculate the appropriate \theta_w so that it satisfies the flux and implement it as a dirichlet condition.

When I calculate Nu, defined as
Nu = \frac{1}{\theta_w-\theta_b}

it doesn't ever reach steady state. When it is supposed to reach steady state, the wall temperature increases more slowly than the bulk temperature and I get a decreasing Nu. Anyone seen this type of behavior before or know whats going on? Am I implementing the constant flux boundary condition properly?

ztdep April 6, 2012 21:46

"and calculate the appropriate so that it satisfies the flux and implement it as a dirichlet condition"
Could you pleaase explain" implement the second kind bc as a first kind".

at the heat flux bc, the boundary condition should like
partial(theta)/partial(n)=?

new_at_this April 6, 2012 23:35

so by subbing in \theta the equatioin becomes

q'' = -k\frac{\theta_1-\theta_w}{H\Delta y^*}q''\frac{H}{k}

In my case I have also non dimensionalized y as y*H = y.

I know everything in the above equation except for \theta_w so I can solve for it and then I implement it as a dirichlet condition.


All times are GMT -4. The time now is 16:48.