Define convection coefficient in contact region
I have a giant block of steel cooled by air in a room.
Usually I could just set a convection boundary condition with a certain convection coefficient hf until the block would asymptotically reach the air temperature, but this would mean that the air would always be at a certain constant temperature while cooling the object.
In my case, the block of steel thermal inertia is comparable with the air, so the air will start heating up while the block cools down, until the two will reach an equilibrium temperature.
Because of this, I wanted to model the air around the block as a solid element in order to have a mass and specific heat, and define the convection boundary condition as the contact region type.
How can I do this? Can I give a certain coefficient, say 10W/m2/K, or a coefficient that is a function of temperature?
thanks
Best Answer

Kremella Admin
Hello,
For this problem, you might want to use Ansys Fluent. In Fluent, you will be modeling both the solid and the surrounding fluid air. You will initialize both your solid and air with a certain initial temperature and run a transient simulation to obtain the final equilibrium condition.
I hope this helps.
Thanks.
Karthik
Answers
Hello,
For this problem, you might want to use Ansys Fluent. In Fluent, you will be modeling both the solid and the surrounding fluid air. You will initialize both your solid and air with a certain initial temperature and run a transient simulation to obtain the final equilibrium condition.
I hope this helps.
Thanks.
Karthik
Hi Karthik, thank you for your reply!
Unfortunately I don't have the license for fluent, and it's unlikely I'd be needing it for an application any more elaborated than this. Isn't it possible to simply work on the contact type to simulate this effect, even if not 100% accurate?
You'd need a resistance to represent the fluidsolid heat transfer coefficient but as you'd not be modelling any convection effects the room temperature will be incorrect, which means you may be as well using @Kremella 's approach.
@fdinh
If you want to know the final equilibrium temperature of the system, and not the time it takes to get there, can't you just write out the equation for the total heat energy in the system? At the start, you can calculate the heat energy in the mass of steel at the temperature Ts and the total heat energy in the mass of air at temperature Ta. Assuming no heat leaves the system, solve for the equilibrium temperature.
Thank you for your insight, I see your points. I'll see if I can find an alternative approach to the problem or look into fluent.
Unfortunately I cannot simply do an energy balance of the system because I want to see the evolution of the temperature inside and there's also other parameters into play other than the ones I stated.
Excellent! Let me mark this as 'Resolved' for now. Please let us know if you need any additional help.
Thanks.
Karthik