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heat transfer - surface to surface radiation: simple test case doesn't match theory
Posted 21 avr. 2022, 12:54 UTC−4 Version 5.6 2 Replies
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I must be missing something important, but I have a very simple test case (sphere inside a sphere) that I'm checking against theory and it's not matching. I have surface-to-surface radiation between the 2 sphere surfaces and I'm (trying to) apply power to the inner sphere while keeping the outer sphere at a set temperature. I'm new to comsol radiation and there are many things I don't understand yet, which is why I was trying to match a simple test case. (the geometry is this view factor model: https://www.comsol.com/model/view-factor-computation-20701)
When I check the temperature of the inner sphere against theory, the comsol temperature is always too low. For theory, wikipedia (https://en.wikipedia.org/wiki/Thermal_radiation#Radiative_heat_transfer) says:
Prad = sigma * A1 * F12 * (T1.^4 - T2^4)
F12 = (r1/r2)^2
I solve Prad = Pheat to get:
T1 = ((Pheat + sigma * A1 * F12 * T2^4)/(sigma * A1 * F12))^(1/4)
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Evidently I also don't understand surface-to-ambient radiation either. When I use surface-to-ambient radiation, I get way more cooling that I expect. When I manually enter Prad, I get the correct temperature.
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Sorry, turns out I made a stupid mistake on the area. I don't see a way to delete this post - there is no problem.