[itsme_kit]

Hi

I just gone through one of the ansys tutorials named in 'Modeling Radiation and Natural Convection'

I wonder what gonna happen if we exclude the radiation model

Obviously there will be no radiative heat transfer, so in this case what's the main method in heat transfer? convection or conduction?

[P.Charoen-amornkitt]

From my understanding, real basic mechanisms of heat transfer are radiation and conduction. Convection is just conduction that includes the motion of fluids. So, you have to ask yourself that does the fluids in your model moves? And the best thing that could describe 'which mechanism is dominated' between convection and conduction is Nusselt number. hD/k .. I think most cases convection is dominated

Best Regards,
Patcharawat

[itsme_kit]

Originally Posted by P.Charoen-amornkitt

From my understanding, real basic mechanisms of heat transfer are radiation and conduction. Convection is just conduction that includes the motion of fluids. So, you have to ask yourself that does the fluids in your model moves? And the best thing that could describe 'which mechanism is dominated' between convection and conduction is Nusselt number. hD/k .. I think most cases convection is dominated

Best Regards,
Patcharawat

Hi Patcharawat

Good to hear from you

Actually for this case, initially the air is stationary and no external force exerted on air. And then, because of the temperature gradient, buoyant-driven flow turns up. Maybe at the beginning, only conduction takes place to produce the temperature gradient, as time elapses, both convection and conduction exist. Is my understanding correct

Thanks in advance

[P.Charoen-amornkitt]

At first, the air on the hot surface is gained heat by conduction. After that bouyancy force occurs since density of hot air is less than cold air. Then the natural convection mechanism will take place since convection is from conduction + advection, which means convection has included conduction already. So, I think that it's only convection that remains.

Best Regards,
Patcharawat

[itsme_kit]

Originally Posted by P.Charoen-amornkitt

At first, the air on the hot surface is gained heat by conduction. After that bouyancy force occurs since density of hot air is less than cold air. Then the natural convection mechanism will take place since convection is from conduction + advection, which means convection has included conduction already. So, I think that it's only convection that remains.

Best Regards,
Patcharawat

Let's simplify the phenomenon further, in case that constant density is assumed, as a result, no buoyant force, no air movement. However, we still can get temperature gradient, so in this case, is it only conduction existed

Thanks

[P.Charoen-amornkitt]

Yes, if no buoyancy force, no external force, no radiation, only the conduction heat transfer exists.