Conduction shape factor tray insulation top/bottom

Symbol
$S_{tw,T}$
Formulas
$\frac{\frac{\pi}{2}}{0.785\ln\left(\frac{w_{t}+2t_{t}}{w_{t}}\right)}$$(w_t+2t_t)$ / $w_t$ ≤ 1.4
$\frac{\frac{\pi}{2}}{0.93\ln\left(\frac{0.948\left(w_{t}+2t_{t}\right)}{w_{t}}\right)}$$(w_t+2t_t)$ / $w_t$ > 1.4