The Enclosed Radiation component models the thermal radiation emitted in enclosed space consisting of multiple surfaces as a result of their temperatures.

Total emissive power of the blackbody is:

$\mathrm{E\_\_b\_\_i}\= \mathrm{\σ} \cdot {\mathrm{T\_\_i}}^4$

And, the relationship of the irradiation $G$ and the radiosity $J$  is defined with:

$J\=\mathrm{\ε}\cdot \mathrm{E\_\_b}\+\left(1-\mathrm{\ε}\right)\cdot G$

The net energy leaving the surface is the difference between the irradiation and the radiosity:

$\frac{\mathrm{Qflow}}{A}\=J-G$

Then, the heat flow rate is:

$\frac{\mathrm{Qflow}}{A}\=J-\frac{J-\mathrm{\ε}\cdot \mathrm{E\_\_b}}{1-\mathrm{\ε}}$

Thus, the following equation is obtained:

$\mathrm{Qflow\_\_i}\= \frac{\mathrm{\ε\_\_i}\cdot \mathrm{A\_\_i}}{1-\mathrm{\ε\_\_i}}\cdot \left(\mathrm{E\_\_b\_\_i}-\mathrm{J\_\_i}\right)$

Finally, the equation is generalized:

$\mathrm{Qflow\_\_i}\= \frac{\mathrm{\ε\_\_i}\cdot \mathrm{A\_\_i}}{1-\mathrm{\ε\_\_i}}\cdot \left(\mathrm{\_\_} \mathrm{\sigma } \cdot {\mathrm{T\_\_i}}^4-\mathrm{J\_\_i}\right)$......(1)

Regarding the exchange of radiant energy by two surfaces:

${\mathrm{Qflow\_\_1\−2}}^{}\=\mathrm{J\_\_1}\cdot \mathrm{A\_\_1}\cdot \mathrm{F\_\_12}-\mathrm{J\_\_2}\cdot \mathrm{A\_\_2}\cdot \mathrm{F\_\_21}$

And,

$\mathrm{A\_\_1}\cdot \mathrm{F\_\_12}\=\mathrm{A\_\_2}\cdot \mathrm{F\_\_21}$

So,

${\mathrm{Qflow\_\_1\−2}}^{}\=\mathrm{A\_\_1}\cdot \mathrm{F\_\_12}\cdot \left(\mathrm{J\_\_1}-\mathrm{J\_\_2}\right)$

Based on the above equation, the generalized expression is obtained:

$\mathrm{Qflow\_\_i}\=\sum _{i\=1}^{\mathrm{numNodes}}\mathrm{A\_\_i}\cdot \mathrm{F\_\_i,k}\cdot \left(\mathrm{J\_\_i}-\mathrm{J\_\_k}\right)......\left(2\right)$

As the implementation of this component, (1) and (2) are used. Additionally, to correct the heat flow rate, the correction factor $\mathrm{cor}$ is applied, if Use correction input is true.

	References
	[1] : J. P. Holman. "Heat Transfer Ninth Edition", McGraw-Hill Higher Education.

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