| Topic: |
Science > Physics |
| User: |
"Joel Sapp" |
| Date: |
22 Feb 2005 12:22:50 PM |
| Object: |
Heat Loss calculation |
Hello,
I would like to calculate the heat loss of insulated sphere. This
sphere would be inside a slightly larger sphere. Its surface has a
mirrored coating that is 97% reflective to IR. It could be higher but I
am not sure of the highest levels of reflectivity. The gap between the
two spheres is evacuated and it is magnetically levatated so that it
never makes physical contact with the outer sphere.
If the inner sphere is at 4K and air temperature outside the outer
sphere is 20 Celcius and the inner sphere radius is .5 meters, what
would be the heat loss hour.
Thanks for your help.
Sincerely,
Joel Sapp
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| User: "Tony" |
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| Title: Re: Heat Loss calculation |
22 Feb 2005 02:38:52 PM |
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Joel, I'd like to assume you know the equations for black body
radiation. Modify it for the emmissivity you've mentioned, look up how
to calculate the area on the surface of the sphere, and you should be
home free.
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| User: "Joel Sapp" |
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| Title: Re: Heat Loss calculation |
22 Feb 2005 03:02:35 PM |
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Tony-Thanx for pointing me in the right direction.
- Joel
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| User: "Tony" |
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| Title: Re: Heat Loss calculation |
22 Feb 2005 05:45:17 PM |
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Brief caution: 97% reflectivity suggests only 3% emissivity
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| User: "Uncle Al" |
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| Title: Re: Heat Loss calculation |
22 Feb 2005 06:03:42 PM |
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Tony wrote:
Brief caution: 97% reflectivity suggests only 3% emissivity
Where in the spectrum is reflectivity measured? A visible mirror can
be black in the IR. A 4K interior separated from an ambient temp
exterior by only mirrored surfaces and a Dewar vacuum space won't be a
heat leak, it will be a heat hemorrhage.
Have you ever handled liquid helium?
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "Tony" |
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| Title: Re: Heat Loss calculation |
22 Feb 2005 08:22:48 PM |
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LH? You betcha. But the question is framed like a homework question,
and I think he now knows how to proceed. The physical embodiment of the
experiment would be a task, perhaps even for you.
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| User: "Uncle Al" |
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| Title: Re: Heat Loss calculation |
22 Feb 2005 08:34:18 PM |
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Tony wrote:
LH? You betcha. But the question is framed like a homework question,
and I think he now knows how to proceed. The physical embodiment of the
experiment would be a task, perhaps even for you.
Supercon Nb/Sn hollow sphere containing liquid helium, with a vent.
The only question is whether it will boil like an insane volcano or
flat out explode.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
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