Substitution coefficient for the calculation of the thermal resistance to ambient.

Symbol
$u$
Unit
-
Formulae
$\frac{2 L_{\mathrm{c}}}{Do_{\mathrm{d}}}$cable in duct or pipe
$\frac{2 L_{\mathrm{c}}}{D_{\mathrm{e}}}$cable not in duct or pipe
$\frac{2 L_{\mathrm{c}}}{D_{\mathrm{hs}}}$heat source
$\frac{2 L_{\mathrm{cm}}}{Do_{\mathrm{t}}}$tunnel
Related
$D_{\mathrm{e}}$
$D_{\mathrm{hs}}$
$Do_{\mathrm{d}}$
$Do_{\mathrm{t}}$
$L_{\mathrm{c}}$
$L_{\mathrm{cm}}$
Used in
$T_{\mathrm{4iii}}$