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shashank312 December 9, 2011 04:05

Negative Heat Flux
 
What is FLUENT's definition of negative heat flux?!

I am calculating forced convection over a heated solid (heat generation for solid considered). And when I report heat flux contours at the center-surface of the solid, I see negative heat flux values. That obviously means that the solid is sucking heat from the fluid. How is that possible if the liquid is below the temperature of the solid wall (wall in contact with the liquid zone)?! Could it be a numerical error or does FLUENT calculate the heat flux incorrectly?

Please share your views & queries if you have any.

Thanks,

Shashank

sifou December 9, 2011 08:16

hello

in Fluent : q= h* (Twall-Tfluid) then if Twall > Tfluid automatically you will have a negative heat flux ( but the numerical result is right).

For the visualization ( and comparison) of the result, it is just necessary to create a new function (qq=-q) with the custom field functions option.

shashank312 December 9, 2011 16:40

Dude, you just contradicted your own statement. How can there be negative flux if Twall is greater than Tfluid. Look at the frikkin formula!

If the wall is heated then the heat flux would be in the direction perpendicular to the plane of the wall and towards the fluid region. If I see a negative flux in such a case, it means that fluid is heating the wall, which is quite possible, and that's what I want to know. How?!

Could it be the vortex structures causing such a drop in the heat transfer rate?

sifou December 9, 2011 18:00

If you have zones of recirculation ( vortex), you must know that generally the heat transfer are reduced in these zones where the convectif effect is less dominating than that diffusive (the fluid is slowed down) in these zones the number of Nusselt records its lowest values.


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