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Tunnel inner diameter

For shapes such as squares or rectangular ducts and tunnels where the height and width are comparable, the characteristic dimension for internal-flow situations is taken to be the hydraulic diameter, defined as $D=4*A/P$, where A is the cross-sectional area, and P is the wetted perimeter. The wetted perimeter for a tunnel is the total perimeter of all inner tunnel walls that are in contact with the flow.

For circular tunnels, the diameter is an input value.

Symbol
$Di_t$
Unit
m
Formulae
$\frac{4A_t}{2w_t+2h_t}$
Related
$A_t$
Cross-sectional area of the tunnel [m$^2$]
$h_t$
Inner height [m]
$w_t$
Inner width [m]
Used in
$A_t$
Cross-sectional area of the tunnel [m$^2$]
$d_t$
Channel covering [m]
$Do_t$
Tunnel/trough outer diameter [m]
$h_t$
Inner height [m]
$\mathrm{Re}_{air}$
Reynolds number for air
$T_{tw}$
Thermal resistance of tunnel wall [K.m/W]