Radiation shape factor from object surface to ambient tunnel or free air considering the view factor for one system and for concentric cylindrical annuli (cable to duct) such as in a riser/J-tube.
| $\frac{1-F_{m}}{1-F_{m} \left(1-K_{t}\right)}$ | in tunnel or free air |
| $\frac{1}{1+\frac{1-\epsilon_{e}}{\epsilon_{e}}+\frac{A_{er} \left(1-\epsilon_{di}\right)}{A_{di} \epsilon_{di}}}$ | riser/J-tube single cable |
| $\frac{1}{1+\frac{\eta_{e}}{\epsilon_{e}}+\frac{\zeta_{er} A_{er} \eta_{di}}{A_{di} \epsilon_{di}}}$ | riser/J-tube touching cables |
| $\frac{\epsilon_{rad} \epsilon_{t}}{3.2-\epsilon_{rad}-\epsilon_{t}}$ | cable pack—tray cover, Saadat2017 |
