Negative Heat Flux

shashank312 · December 9, 2011, 04:05

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.

December 9, 2011, 04:05	Negative Heat Flux	#1
shashank312 Member Shashank Join Date: Apr 2011 Posts: 74 Rep Power: 15	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

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[Other] mesh airfoil NACA0012	anand_30	OpenFOAM Meshing & Mesh Conversion	13	March 7, 2022 18:22
[blockMesh] BlockMesh FOAM warning	gaottino	OpenFOAM Meshing & Mesh Conversion	7	July 19, 2010 15:11
Why does negative heat flux come?	abhi007shek	FLUENT	1	August 6, 2009 17:08
[blockMesh] Axisymmetrical mesh	Rasmus Gjesing (Gjesing)	OpenFOAM Meshing & Mesh Conversion	10	April 2, 2007 15:00
why the value of wall heat flux is negative?	prayskyer	CFX	5	September 29, 2006 08:32

December 9, 2011, 08:16		#2
sifou New Member H.A Join Date: Oct 2011 Posts: 4 Rep Power: 15	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.

December 9, 2011, 16:40		#3
shashank312 Member Shashank Join Date: Apr 2011 Posts: 74 Rep Power: 15	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?

December 9, 2011, 18:00		#4
sifou New Member H.A Join Date: Oct 2011 Posts: 4 Rep Power: 15	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.