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Thermal resistance of steel pipe filling

The thermal resistance of the gas or oil between the surface of the cores and the pipe is calculated in the same way as that part of $T_{4i}$ which is between a cable and the internal surface of a duct.

Symbol
$T_{spf}$
Unit
K.m/W
Formulae
$\frac{U_{spf}}{1+0.1\left(V_{spf}+Y_{spf} \theta_{spf}\right) D_{eq}}$
Related
$D_{eq}$
Equivalent diameter of a group of round objects [mm]
$\theta_{spf}$
Mean temperature of the medium in the steel pipe [°C]
$U_{spf}$
Constant U for pipe-type cables [K.m/W]
$V_{spf}$
Constant V for pipe-type cables [K.m/W]
$Y_{spf}$
Constant Y for pipe-type cables [K.m/W]
Used in
$T_2$
Thermal resistance of armour bedding [K.m/W]