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heat transfer in a composite spherical solid

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I am modeling a composite spherical solid of radius b, of which an inner core, 0 <= r < a , is composed of gold and has temp 100 degrees Kelvin and an outer shell a < r < b of a water medium with temp 10 degrees Kelvin. I am using the transient heat transfer in the Comsol metaphysics module. The heat diffuses like it should normally (exponentially decreases as the radius increases) except for a bump when the heat of the gold begins to decrease and a dip as the temperature begins to stablize in the water medium. For example say at t= 1 s with a = 10 m and b = 20 m the temp at a particular radius of the gold starts to decrease like it should and the temp of the water medium close to the gold start to increase except the gold temp increases to a temp higher than its initial temp before it starts to decrease and at the end of the diffusion the water medium decreases below its initial temperature before rising back to the 10 K that was its initial temp. Does anyone have any idea of what I could be doing wrong. Thanks.

2 Replies Last Post Jul 14, 2009, 3:58 AM EDT
David Wenger Certified Consultant

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Posted: 1 decade ago Jul 14, 2009, 3:55 AM EDT
What time steps are you using?

Regards

David Wenger
www.comsol.de/company/consultants/wenger/
What time steps are you using? Regards David Wenger www.comsol.de/company/consultants/wenger/

David Wenger Certified Consultant

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Posted: 1 decade ago Jul 14, 2009, 3:58 AM EDT
By the way: "degrees Kelvin" do not exist. Either you use "Kelvin" or "degrees Celsius" (in science: Kelvin). 10K is a very low temperature. If you used the material database, this might be the mistake because the properties are not specified there properly.

David Wenger
www.comsol.de/company/consultants/wenger/
By the way: "degrees Kelvin" do not exist. Either you use "Kelvin" or "degrees Celsius" (in science: Kelvin). 10K is a very low temperature. If you used the material database, this might be the mistake because the properties are not specified there properly. David Wenger www.comsol.de/company/consultants/wenger/

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