Heat flow inside a body

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  • Last Post 04 April 2018
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lia_m posted this 22 March 2018

Hello,

I would like to know if it is possible to create a heat flow inside of a body. In my example it shall represent a simplification of the heat that is dissipated inside a wire when using an electromagnet. The total heat dissipation of the wire is 12 W and I want it to originate in the center of the wire.

Thanks for any help!

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peteroznewman posted this 22 March 2018

Hello,

Yes, it is possible to create a heat flow inside a body.  I assume a wire means a conductive core at the center of an insulating sheath. So when you say the heat originates in the center of the wire, you mean in the core.

The electromagnet causes a current to flow in the core, which has resistance and experiences Joule heating. The current flows though the cross-section of the core which has cross-sectional area, A.  The length of the wire is L, therefore the volume of the core, V = LA.  If the volume is in mm^3, then you can apply Internal Heat Generation, Q to the body in watts/mm^3, or in your case 12/V.

The insulating sheath and the core both have a material property of thermal conductivity that controls how easily heat flows through the material. Let's say the core is copper and the sheath is plastic.

I assume the wire is dissipating the heat to air through convection. A convection coefficient describes how fast the air can take away the heat from the surface of the sheath.

The solution shows the temperature profile. The core is a uniform 131 C and the surface of the sheath is 39 C.

An ANSYS 17.2 archive is attached that can be opened with any newer version of ANSYS using the Workbench menu, File, Restore Archive.

P.S. You also posted about heat flow in zero gravity where there is no natural convection, though you can always use a fan for forced convection. If you wanted no fan, then you could add a third body to the problem, which would be air, which has an even lower conductivity than the plastic. Then you would remove the convection and add a temperature boundary condition and input the temperature of the walls of the spacecraft that touch the air inside. The walls lose heat through radiation to space.

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lia_m posted this 04 April 2018

Hey, thank you very much for your answer, it helped me a lot!

What I dont really get is why you would use a temperature boundary condition for the walls of the spacecraft, because if I understand right such a condition means that the temperature doen`t change but as you wrote, they lose heat through radiation to space.

Thanks again!

peteroznewman posted this 04 April 2018

I mean the spacecraft has thermal management systems that keep the temperature inside at some steady state value while the outside wall is losing heat to space. 

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