Thermal resistance 21 of multi-layer backfill

Thermal resistance of 1st segment along flow path $\Phi_2$ of the multi-layer backfill method.

Symbol
$R_{q21}$
Unit
K.m/W
Formulae
$\frac{\rho_b \ln\left(\frac{w_{b4}+C_{b3} \left(\frac{d_{b3}+d_{b4}}{2}-w_{b4}\right)}{r_o}\right)}{\arctan\left(\frac{s_{b3}}{w_{b4}}\right)+\arctan\left(\frac{s_{b4}}{w_{b4}}\right)}$