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Different temperature results for 2D and 3D

Posted 11 janv. 2020, 09:55 UTC−5 Heat Transfer Version 5.5 4 Replies

Andreas
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I have an object that is cooling down due to heat flux. As I understand it, when only a 2D object is modeled, COMSOL takes a default depth of 1m for proper calculation of ie density and heat flux parameters. However, when I take the same object with the same parameters and material properties, but this time do it in 3D with 1m depth, my time dependent study gives me different (/decreased) temperature changes than in 2D.

What am I missing?

4 Replies Last Post 11 janv. 2020, 14:10 UTC−5
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago 11 janv. 2020, 10:16 UTC−5

Andreas,

are the boundary conditions at the end faces equivalent in 2D and 3D?

Cheers Edgar

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Andreas, are the boundary conditions at the end faces equivalent in 2D and 3D? Cheers Edgar
Dave Greve
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Posted: 5 years ago 11 janv. 2020, 12:45 UTC−5

In 2D you are modeling a medium infinitely thick in the z direction. Any volume-dependent quantity is calculated for a 1 m section of the infinitely thick medium. There is no heat flux in the z direction.

In 3D there can be heat loss (gain) on the front and back (+z and -z) faces. The problems are not equivalent.

In 2D you are modeling a medium infinitely thick in the z direction. Any volume-dependent quantity is calculated for a 1 m section of the infinitely thick medium. There is no heat flux in the z direction. In 3D there can be heat loss (gain) on the front and back (+z and -z) faces. The problems are not equivalent.
Edgar J. Kaiser Certified Consultant
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Posted: 5 years ago 11 janv. 2020, 13:21 UTC−5

Thermal insulation at the front and back face can make 3D equivalent to 2D if the other BC are chosen appropriately.

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Thermal insulation at the front and back face can make 3D equivalent to 2D if the other BC are chosen appropriately.
Andreas
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Posted: 5 years ago 11 janv. 2020, 14:10 UTC−5

Thermal insulation at the front and back face can make 3D equivalent to 2D if the other BC are chosen appropriately.

Yes there is thermal insulation at the front and back face.

So assuming all the boundary conditions are the same, there should be exactly the same result? Although I think the boundary conditions are equal, there probably is a mistake in there somewhere.

Thanks for your help.

>Thermal insulation at the front and back face can make 3D equivalent to 2D if the other BC are chosen appropriately. Yes there is thermal insulation at the front and back face. So assuming all the boundary conditions are the same, there should be exactly the same result? Although I think the boundary conditions are equal, there probably is a mistake in there somewhere. Thanks for your help.

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