Constant steady state temperature

Niels V · November 21, 2020, 09:58

Dear all,

My simulation basically consists of a heated object with air flow over it and I need an air velocity profile and temperature profile in steady state. The one issue I am encountering though is that I can't seem to figure out how to give my heated object a certain temperature in this steady state.

I tried setting the heat transfer of my object to "Thermal Energy" and setting an initial temperature but then, of course, in steady state my object will get the same temperature as the airflow that is coming in.

I also tried setting the heat transfer of my object domain to "isothermal", that results in my object having the correct temperature in steady state but there won't be heat transfer to the air, which I need.

The last thing that came to mind was setting an interface boundary condition that results in a constant temperature of the object surface but the only option I get is a "Conservative interface flux".

In short; I need to give my object a certain temperature in steady state and there has to be heat transfer between the air and object.

I have watched some video tutorials and read some manuals but I can't seem to figure it out.

Thanks in advance,
Niels

Gert-Jan · November 21, 2020, 14:35

When using Isothermal, everything will have the same temperature. No energy equation will be solved.
When using Thermal Energy, the energy equation will be solved. And your solution will adapt to your boundary conditions. In your case you set an inlet temperature for the air and a surface temperature of the object to cool. This will give you a temperature profile in air.

How difficult can it be?

Niels V · November 21, 2020, 15:27

That is what I have been trying, setting a boundary condition for my surface to have a constant temperature. Yet I can't seem to find a way to implement this?
The only option I get when inserting a boundary condition on the surface of my object is a "conservative interface flux".

ghorrocks · November 21, 2020, 15:49

That is the condition for an interface, not a boundary condition.

If you know the temperature of the object then you don't need to model it. So remove the object you know the temperature of from your model and replace the interface boundary with a thermal boundary condition - in your case maybe a convective boundary condition, or maybe a constant temperature.

Niels V · November 21, 2020, 16:16

Thank you! That is something I didn't consider and will most likely solve my issue.

November 21, 2020, 09:58	Constant steady state temperature	#1
Niels V New Member Join Date: Nov 2020 Posts: 3 Rep Power: 5	Dear all, My simulation basically consists of a heated object with air flow over it and I need an air velocity profile and temperature profile in steady state. The one issue I am encountering though is that I can't seem to figure out how to give my heated object a certain temperature in this steady state. I tried setting the heat transfer of my object to "Thermal Energy" and setting an initial temperature but then, of course, in steady state my object will get the same temperature as the airflow that is coming in. I also tried setting the heat transfer of my object domain to "isothermal", that results in my object having the correct temperature in steady state but there won't be heat transfer to the air, which I need. The last thing that came to mind was setting an interface boundary condition that results in a constant temperature of the object surface but the only option I get is a "Conservative interface flux". In short; I need to give my object a certain temperature in steady state and there has to be heat transfer between the air and object. I have watched some video tutorials and read some manuals but I can't seem to figure it out. Thanks in advance, Niels

November 21, 2020, 15:49		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,819 Rep Power: 144	That is the condition for an interface, not a boundary condition. If you know the temperature of the object then you don't need to model it. So remove the object you know the temperature of from your model and replace the interface boundary with a thermal boundary condition - in your case maybe a convective boundary condition, or maybe a constant temperature. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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November 21, 2020, 14:35		#2
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,887 Rep Power: 27	When using Isothermal, everything will have the same temperature. No energy equation will be solved. When using Thermal Energy, the energy equation will be solved. And your solution will adapt to your boundary conditions. In your case you set an inlet temperature for the air and a surface temperature of the object to cool. This will give you a temperature profile in air. How difficult can it be?

November 21, 2020, 15:27		#3
Niels V New Member Join Date: Nov 2020 Posts: 3 Rep Power: 5	That is what I have been trying, setting a boundary condition for my surface to have a constant temperature. Yet I can't seem to find a way to implement this? The only option I get when inserting a boundary condition on the surface of my object is a "conservative interface flux".

November 21, 2020, 16:16		#5
Niels V New Member Join Date: Nov 2020 Posts: 3 Rep Power: 5	Thank you! That is something I didn't consider and will most likely solve my issue.