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Outer diameter

Diameter in meters used to calculate the thermal resistance of cables, ducts or heat source in air or for calculations where metric dimension is required.

Symbol
$D_o$
Unit
m
Formulas
$\frac{D_e}{1000}$cables not in duct
$\frac{Do_d}{1000}$cables in duct
$\frac{D_e}{1000}$heat sources
$D_{prot}$PAC/GIL
Related
$D_e$
External diameter object [mm]
$D_{prot}$
Diameter protective cover [m]
$Do_d$
Outer diameter duct [mm]
Used in
$A_e$
Surface of object [m$^2$]
$A_{er}$
Surface of object [m$^2$]
$\alpha_{sa}$
Heat transfer coefficient convection [W/(K.m$^2$)]
$\beta_6$
Factor $|1-\beta(6)|$
$\beta_t$
Attainment factor cable surface—ambient
$D_{ext}$
Diameter external [m]
$\delta_d$
Distance cable—duct [m]
$\Delta \theta_{e,t}$
Transient temperature rise outer surface [K]
$\Delta \theta_{sun}$
Temperature difference conductor—enclosure [K]
$F_m$
Mutual radiation coefficient
$G_{od}$
Aspect ratio object/duct
$\gamma_t$
Attainment factor cables
$\mathrm{Gr}_L$
Grashof number, ground—air
$\mathrm{Gr}_{prot}$
Grashof number surface→air
$h_{bs}$
Heat dissipation coefficient for black surfaces in free air [W/m$^2$/K$^{5/4}$]
$h_{conv,gd}$
Heat transfer coefficient convection gas—duct [W/(K.m$^2$)]
$h_{conv,int}$
Heat transfer coefficient convection cable—riser [W/(K.m$^2$)]
$h_{conv,og}$
Heat transfer coefficient convection cable—gas [W/(K.m$^2$)]
$h_{conv,sa}$
Heat transfer coefficient convection surface—air [W/(K.m$^2$)]
$h_{rad,int}$
Heat transfer coefficient radiation cable—riser [W/(K.m$^2$)]
$K_A$
Coefficient K in air
$K_{od}$
Diameter ratio object/duct
$L_{deep}$
Deep burial thermal inertia equivalent depth [m]
$\mathrm{Nu}_{int}$
Nusselt number cable—riser
$\mathrm{Nu}_{og}$
Nusselt number cable—gas
$r_o$
Radius of object [m]
$r_{z6}$
Radius outersheath [m]
$\mathrm{Re}_{air}$
Reynolds number air
$T_{4iii}$
Thermal resistance ambient [K.m/W]
$T_{sa}$
Thermal resistance convection object—air [K.m/W]
$T_{st}$
Thermal resistance radiation object—tunnel [K.m/W]
$u$
Substitution coefficient u
$W_{conv,int}$
Convective heat transfer cable→riser [W/m]
$W_{conv,og}$
Convective heat transfer cable→gas [W/m]
$W_{conv,sa}$
Convective heat transfer, surface→air [W/m]
$W_{di}$
Losses between cable and riser [W/m]
$W_{rad,sa}$
Radiation heat transfer surface—air [W/m]
$W_{sun}$
Heat transfer solar radiation air→surface [W/m]
$\zeta_{er}$
Radiation shape factor touching cables