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Thermal Insulation Boundary Condition

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Thermal Insulation is the default B.C. for heat transfer. I have tried adding "radiate-to-ambient", with known emissivity and ambient temperature, as a boundary condition to override this insulation. Despite my manually deselecting these boundaries, they always seem to reappear as insulated.

Your thoughts, please.

4 Replies Last Post Jun 16, 2011, 11:37 a.m. EDT

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Posted: 1 decade ago Jun 16, 2011, 10:02 a.m. EDT
Trying for a bump with more detail.

I have air moving through a duct, forced through a heat sink, and out another duct. All resting on a metallic.

I would like several outer boundaries, particularly of duct, heat sink, and base of to radiate-to-ambient. I do not wish them to have thermal insulation, but that seems to be a recurring default.

Thanks for your help.
Trying for a bump with more detail. I have air moving through a duct, forced through a heat sink, and out another duct. All resting on a metallic. I would like several outer boundaries, particularly of duct, heat sink, and base of to radiate-to-ambient. I do not wish them to have thermal insulation, but that seems to be a recurring default. Thanks for your help.

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Posted: 1 decade ago Jun 16, 2011, 10:53 a.m. EDT
Hi,

I am not sure I understand the problem. The defualt boundary condition is 'thermal insulation' in order to have something different that BC must be overridden, that is achieved by adding a different boundary condition and selecting that surface/edge/domain that must have a different boundary condition.

Cheers
Hi, I am not sure I understand the problem. The defualt boundary condition is 'thermal insulation' in order to have something different that BC must be overridden, that is achieved by adding a different boundary condition and selecting that surface/edge/domain that must have a different boundary condition. Cheers

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Posted: 1 decade ago Jun 16, 2011, 11:16 a.m. EDT
I believe this is what I have done by selecting "radiate-to-ambient". I have one ambient temperature, and one surface emissivity for each radiating material.

These surfaces appear selected as "radiate-to-ambient", but also appear as insulated. When I de-select them in Thermal Insulation, they automatically revert to thermal insulation.

Should radiate-to-ambient not be an adequate boundary condition to override the default thermal insulation?
I believe this is what I have done by selecting "radiate-to-ambient". I have one ambient temperature, and one surface emissivity for each radiating material. These surfaces appear selected as "radiate-to-ambient", but also appear as insulated. When I de-select them in Thermal Insulation, they automatically revert to thermal insulation. Should radiate-to-ambient not be an adequate boundary condition to override the default thermal insulation?

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Posted: 1 decade ago Jun 16, 2011, 11:37 a.m. EDT
Hi,

If you add the 'Surface-to-Ambient Radiation' and select the desired boundary then in the default 'thermal insulation' boundary it still apears with a writing between parenthesis 'overridden' which means that thermal insulation does not apply any more.

Cheers
Hi, If you add the 'Surface-to-Ambient Radiation' and select the desired boundary then in the default 'thermal insulation' boundary it still apears with a writing between parenthesis 'overridden' which means that thermal insulation does not apply any more. Cheers

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