Thermal resistance 31 of multi-layer backfill

Thermal resistance of 1st segment along flow path $\Phi_3$ of the multi-layer backfill method.

Symbol
$R_{q31}$
Unit
K.m/W
Formulae
$\frac{\rho_b \ln\left(\frac{s_{b4}+C_{b2} \left(d_{b4}-s_{b4}\right)}{r_o}\right)}{\arctan\left(\frac{w_{b4}}{s_{b4}}\right)}$