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Thermal resistance of medium in the air-filled pipe with objects

Thermal resistance between ducts and air-filled pipe based on IEC 60287-2-1 for cables in ducts.

Symbol
$T_{4pi}$
Unit
K.m/W
Formulae
$\frac{U_p}{1+0.1\left(V_p+Y_p \theta_{at}\right) D_{eq}}$
Related
$D_{eq}$
Equivalent diameter of a group of round objects [mm]
$\theta_{at}$
Air temperature under load [°C]
$U_p$
Constant U for air-filled pipe with objects [K.m/W]
$V_p$
Constant V for air-filled pipe with objects [K.m/W]
$Y_p$
Constant Y for air-filled pipe with objects [K.m/W]
Used in
$\Delta \theta_{air}$
Temperature increase of air [K]
$T_{4db}$
Correction of thermal resistance for backfill [K.m/W]
$T_{4ss}$
Steady-state thermal resistance [K.m/W]
$\theta_{di}$
Temperature of duct inner wall [°C]