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[3.5a thermal]Surface to surface radiative exchange
Posted 15 feb 2010, 06:36 GMT-5 1 Reply
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Hello to everyone
I have some problems with surface to surface boundary condition.
I have two parallel surfaces that after conduction analysis display a very similar temperature distribution, that is 54.05 °C for surface A and 54.01 °C for B surface. Now i want to analyze the model better and i want to insert surface to surface radiation exchange between these two surfaces.
So I create a group for these two surfaces, i insert emissivity and I put 0 K for ambient T, at the end i launch analysis. When my analysis ends i find a temperature distribution on these surfaces that is lower than the lower starting T(54.01°C).
I think that adding only these exchange i should find a T that is between the starting T.
What is the problem? Watching the equation explanation for radiation i find that also in surface to surface there is ambient interaction. can I change the equation to erase this contribution?
Thank you in advance
Luca
I have some problems with surface to surface boundary condition.
I have two parallel surfaces that after conduction analysis display a very similar temperature distribution, that is 54.05 °C for surface A and 54.01 °C for B surface. Now i want to analyze the model better and i want to insert surface to surface radiation exchange between these two surfaces.
So I create a group for these two surfaces, i insert emissivity and I put 0 K for ambient T, at the end i launch analysis. When my analysis ends i find a temperature distribution on these surfaces that is lower than the lower starting T(54.01°C).
I think that adding only these exchange i should find a T that is between the starting T.
What is the problem? Watching the equation explanation for radiation i find that also in surface to surface there is ambient interaction. can I change the equation to erase this contribution?
Thank you in advance
Luca
1 Reply Last Post 16 feb 2010, 02:08 GMT-5
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Posted:
1 decade ago
Hi
I do not understand your T=0K for ambient, I would have expected something else, even in outer space you have T>0, do you have air or vacuum between the surfaces ?
On the other side radiative exchange goes as the forth power of T
Q=sigma*(T1[1/K] - T2[1/K])^4
WITH BOTH TEMPERATURES IN K
so if you have less than 1°C temperature difference, the heat exchange is really tiny and insignificant, sigma the Stephan Boltzmann constant is 56.7E-9 W/m^2/K^4 or 57nW/m^2 for one degree, not much heat
however it the ambient temperature is 0°C it's different, by some 300 no ?
good luck
Ivar
I do not understand your T=0K for ambient, I would have expected something else, even in outer space you have T>0, do you have air or vacuum between the surfaces ?
On the other side radiative exchange goes as the forth power of T
Q=sigma*(T1[1/K] - T2[1/K])^4
WITH BOTH TEMPERATURES IN K
so if you have less than 1°C temperature difference, the heat exchange is really tiny and insignificant, sigma the Stephan Boltzmann constant is 56.7E-9 W/m^2/K^4 or 57nW/m^2 for one degree, not much heat
however it the ambient temperature is 0°C it's different, by some 300 no ?
good luck
Ivar