# Thermal resistance 21 of multi-layer backfill method

Thermal resistance offered by the material in layer 1 along the flow path q2.

Symbol
$R_{q21}$
Unit
K.m/W
Formulae
$\frac{\ln{\left(\frac{2 \left(C_{3} \left(\frac{c_{T}}{2} + \frac{d_{T}}{2} - s_{3}\right) + s_{T}\right)}{D_{o}} \right)}}{k_{3} \left(\operatorname{atan}{\left(\frac{s_{3}}{s_{T}} \right)} + \operatorname{atan}{\left(\frac{s_{4}}{s_{T}} \right)}\right)}$
Related
$c_{T}$
$D_{o}$
$d_{T}$
$k_{3}$
$s_{3}$
$s_{4}$
Used in
$R_{q2}$