Hi,(adsbygoogle = window.adsbygoogle || []).push({});

I searched the forum and the web and can't seem to find my answer, nevertheless I will continue looking.

There might be some obvious answer to this and I'm probably missing something, but in any case this is my question:

I have a sphere inside another sphere with a cavity of air between the spherical planes.

The radius of the outer sphere is about 4 times larger than the inner sphere.

I have a temperature gradient between the two spherical planes, (let's say 100K).

Given my temperature gradient, ratio of the areas, and Boltzmann's law:

Irradiance=[{σ*ε*Area_small*((T_hot)^4)}-{σ*ε*Area_large*((T_cold)^4)}]

my net energy due to radiation is a negative number. The ratio of the area is dominating my difference.

I guess what I'm asking is, what does this negative quantity mean? Energy in this case should still be moving from the inner sphere to the outer sphere directed along the normal path I think?

This is not a homework problem, I'm designing a vessel and need to know what this means as far as heat transfer.

Thanks in advance.

Update:

This is assuming equal emissivity. Although both bodies will be aluminum so I am wondering if emissivity changes much with a temperature difference of 100K?

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# Stefan–Boltzmann Law - Radiation in a Sphere

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