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Old   February 2, 2006, 09:22
Default constant heat flux boundary condition
  #1
Andrew Hayes
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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
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Old   February 2, 2006, 10:00
Default Re: constant heat flux boundary condition
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diaw
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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...
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Old   February 2, 2006, 10:21
Default Re: constant heat flux boundary condition
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Andrew Hayes
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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
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Old   February 2, 2006, 11:31
Default Re: constant heat flux boundary condition
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diaw
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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...
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Old   February 19, 2006, 14:54
Default Re: constant heat flux boundary condition
  #5
upender
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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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