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 Andrew Hayes February 2, 2006 09:22

constant heat flux boundary condition

I am having trouble writing a finite difference scheme for the constant heat flux boundary condition in porous media using the local thermal non-equilibrium model; -kf(dT/dy)= -ks(dT/dy). In which kf is fluid conductivity and ks is solid. This is the boundary condition at the wall. I think I am confused at what exactly is 'at the wall'. Which leads to the problem I am having of definig the 'dy' term.

thanks

 diaw February 2, 2006 10:00

Re: constant heat flux boundary condition

Hi Andrew,

A thought,

The surface heat balance would be,

-kf(dT/dy)= q',flux

where: q',flux is the value of the edge thermal flux you are setting;

You can then set up the dT/dy relationship accordingly. I hope this is of use.

diaw...

 Andrew Hayes February 2, 2006 10:21

Re: constant heat flux boundary condition

that is pretty much how I did it. I was just confused at how I could have a 'kf' at the wall if I hadn't even made it to the fluid yet and was still in the wall. What I did for the fluid temperature was use T(x)=Tin + (q"(width)(x)/(mdot*Cp))to find the fluid temperature at 'dy' from the wall. Then, I back track to get the wall temperature. Then, knowing the dT/dy for the fluid is equal to dT/dy for the solid I can get the solid temperatures.

thanks

 diaw February 2, 2006 11:31

Re: constant heat flux boundary condition

Hi Andrew,

You have a surface heat-balance at the boundary.

From the solid side, you impose the q',flux = q',in/ dA,surface.

The heat entering the surace, from the solid, must exit the surface, into the fluid. This is the -kf*dT/dy*dA,surface term.

You can then construct the appropriate boundary term into that particular FD element.

Have fun.

diaw...

 upender February 19, 2006 14:54

Re: constant heat flux boundary condition

dear sir

i am upender doing mtech in thermal sciences. sir, i would like to know what r the possible methods to maintain constant heat flux in convection over a cylinder.

even if we give the constant heat input it is not possible to maintain constant heat flux every where on the cylinder . can u pls send the experimental setup to maintain the same.. waiting for ur reply

i will be obliged if u can send that.

thanking u sir

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