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Radiation coefficient mutual

Radiation view factor coefficient for radiation thermal resistance calculation within a cable system.

Symbol
$F_m$
Formulae
$0$1 cable
$\frac{1}{\pi} \left(\\arcsin\left(\frac{D_o}{s_{air}}\right)+\sqrt{\left(\frac{s_{air}}{D_o}\right)^2-1}-\frac{s_{air}}{D_o}\right)$2 cables
$\frac{2}{\pi} \left(\\arcsin\left(\frac{D_o}{s_{air}}\right)+\sqrt{\left(\frac{s_{air}}{D_o}\right)^2-1}-\frac{s_{air}}{D_o}\right)$3 cables (middle)
$\frac{1}{\pi} \left(\\arcsin\left(\frac{D_o}{s_{air}}\right)+\sqrt{\left(\frac{s_{air}}{D_o}\right)^2-1}-\frac{s_{air}}{D_o}\right)$3 cables (outer)
$\frac{1}{6}+\frac{1}{\pi} \left(\frac{\pi}{2}-1\right)$3 cables touching trefoil
Related
$D_o$
Outer diameter [m]
$inst_t$
Installation in air inside a room
$\pi$
Archimedes' constant $\pi$
$s_{air}$
Axial spacing between objects [m]
Used in
$K_r$
Radiation shape factor
Choices
Example installationValue
1 cable0
2 cables touching0.182
2 cables spaced 2*D0.081
2 cables spaced 3*D0.054
3 cables touching0.363 (middle cable)
0.182 (outer cables)
3 cables spaced 2*D0.163 (middle cable)
0.081 (outer cables)
3 cables spaced 3*D0.107 (middle cable)
0.054 (outer cables)
3 cables touching trefoil0.348