## Preprocessing

#### Define convection coefficient in contact region

• fdinh
Subscriber
I have a giant block of steel cooled by air in a room.nUsually 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.nIn 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.nBecause 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.nHow can I do this? Can I give a certain coefficient, say 10W/m2/K, or a coefficient that is a function of temperature?nthanksn
• Karthik R
Administrator
Hello,nFor 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. nI hope this helps.nThanks.nKarthikn
• fdinh
Subscriber
Hi Karthik, thank you for your reply!nUnfortunately 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?n
• Rob
Ansys Employee
You'd need a resistance to represent the fluid-solid 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 's approach. n
• peteroznewman
Subscriber
nIf 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.n
• fdinh
Subscriber
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.nUnfortunately 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.n
• Karthik R
Administrator
Excellent! Let me mark this as 'Resolved' for now. Please let us know if you need any additional help.nThanks.nKarthikn
Viewing 6 reply threads
• You must be logged in to reply to this topic.