# Discussion Forum

## Temperature as Boundary Condition

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Good morning, How can I specify a fixed temperature on a point in my model? I know how to impose this condition to boundaries and not to domains, edges and points. Thank you.

5 Replies Last Post Aug 1, 2020, 1:24 PM EDT

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Posted: 6 days ago
Updated: 6 days ago

Hmm. I didn't see a point-setting option for the temperature offered. I found that you can specify a heat source boundary condition on a point, but apparently not a fixed temperature boundary condition. Well, how about a work-around then, since true point-constraint conditions aren't physical in the real world anyway! Yes, there's probably a better way, but it's been two weeks since you posted this question and no one answered. So here's my two cents: If I was in a hurry, and I simply wanted to specify the temperature at a "single point" within a 3D volume, I would probably just put a tiny sphere there (instead of a true point) and specify the temperature on its surface (which is a legitimate boundary). Similarly, if I wanted to specify the temperature at a single point in a 2D model, I would probably just put a tiny circle there (instead of a true point), and specify the temperature on its edge (again, which is a legitimate boundary). For a small enough sphere or circle, the physics calculations of interest to you (at least, in most real-world problems that I can imagine) would be equivalent. Right? Good luck.

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Posted: 5 days ago

More > Pointwise Constraint then Constraint Expression T-273 (to set T to 273).

You may need to enable advanced physics options to see this. Works for edges also, where, for some reason, it is also called Pointwise Constraint.

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Posted: 5 days ago

Hi Dave. Hmm, I had to look for that one! Right-click "Heat Transfer in Solids" or similar, then Show More Options..., then under Physics, click the box to show Equation-based Contributions. OK. Then go back to right-click on Points, and choose Pointwise Constraint.

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Posted: 5 days ago

Dave,

The term Pointwise Constraint is not related to the dimension of the geometrical object to which it is applied,

The constraint is pointwise in the sense that it is applied to all individual mesh nodes in the selection. The opposite is a weak constraint.

-------------------
Henrik Sönnerlind
COMSOL

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Posted: 4 days ago

Yeah, definitely not easy to find. I think I turned it up by looking at some examples on this website. One of the ways to find out how to do things that are not obvious.

The term Pointwise Constraint is not related to the dimension of the geometrical object

I was suggesting that Edgewise Constraint would be more informative.

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