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Post by PeterB on Mar 3, 2011 8:33:09 GMT -4
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Post by Jason Thompson on Mar 3, 2011 9:02:34 GMT -4
Ask him to show why all the heat is from conversion of UV to IR, rather than just incident IR, and then ask him how the heat input to the camera might be affected by the reflective coating it had.
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Post by chew on Mar 3, 2011 11:43:47 GMT -4
In terms of heat loss a camera in a vacuum can only lose heat radiatively. There is no conduction or convection occurring. One earth the camera can lose heat through all three methods. Be sure to point out to him the reverse is true also: on Earth all three methods will also add heat to the camera. The UV comment I took to mean that UV has higher energy than IR and the Earth's atmosphere blocks a lot of UV, therefore sun light in a vacuum generates more heat because of the higher proportion of UV light. But, re-reading it again it makes absolutely no sense. The maximum solar radiation reaching the surface of the Earth is about 1000 watts/meter 2 (with a zenith angle of 0 o). Above the atmosphere (e.g. on the Moon) it's 1367 watts/meter 2. So it's not a lot more. Silver has an emissivity of 0.02. |
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Post by chrlz on Mar 3, 2011 16:44:43 GMT -4
So, them cameras were just sitting out there in the Sun? Never went into shadow as the astronauts moved around? And when they were in the Sun, how much of the camera was being struck by sunlight?
And I'd like to hear more about this UV to IR conversion process...
In other words, let's see some numbers and real heat transfer analysis that takes into account the REALITY. It's just more ill-informed, unsupported handwaving from people who couldn't analyse their way out of a wet brown paper bag.
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Post by PhantomWolf on Mar 3, 2011 17:42:20 GMT -4
Call him on the UV to IR claim, I can't locate anything that seems to relate to anything like that.
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Post by chrlz on Mar 6, 2011 3:06:32 GMT -4
Just for the record, I've thrown a few responses onto that blog (or whatever it is), focusing on a number of issues, including: - in a vacuum, things take a long while to get hot or cold, as there is no conductive or convective heating/cooling. - the cameras were big solid aluminium ones, painted with a suitable reflective silver coating - the cameras were being constantly moved around, so they would have been in shadow often, and when in sunlight, only one half of the surfaces would be illuminated, the others would be radiating heat back out... - that the arm-in-the-sun 'analogy' is ridiculously flawed (see below) - asked any of them to provide thermal transfer calculations... (grin) - asked any of them to provide all the factors that would be necessary to analyse a situation like this properly (after giving them most of them, to complete silence...) - asked if they thought NASA didn’t have suitable previous experience with cameras in space - and of course asked about the miraculous UV to IR process that Tony has invented.. Interestingly, I suspect that our biological/nervous response to getting a UV-induced sunburn is in fact a very large part of why one's arm feels 'hot' when in the Sun. Any biological whizzes here that can comment on that? 'Steve' has responded by saying my posts are too long winded, and that the outback sun 'has cooked your fritter'... I think that's game set and match, but would love to hear other educated opinions...  |
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Post by banjomd on Mar 9, 2011 17:30:30 GMT -4
Interestingly, I suspect that our biological/nervous response to getting a UV-induced sunburn is in fact a very large part of why one's arm feels 'hot' when in the Sun. Any biological whizzes here that can comment on that? I am not a biological whiz and not a dermatologist (I'm an ophthalmologist). If I recall correctly the vasodilation (biological response to UV skin exposure occurs hours later and it does make the skin feel hot however the heat that we feel in the sun is IR warmth. |
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