Free cross-sectional area inside duct

Cross-sectional area of empty duct minus the cross-sectional area of all objects inside the duct.

Symbol
$A_{d_{fill}}$
Unit
mm$^2$
Formulae
$\frac{\pi \left(- D_{e}^{2} + Di_{d}^{2}\right)}{4}$$N_{c} \leq 1$
$\frac{\pi \left(- 2 D_{e}^{2} + Di_{d}^{2}\right)}{4}$$N_{c} \leq 2$
$\frac{\pi \left(- 3 D_{e}^{2} + Di_{d}^{2}\right)}{4}$$N_{c} \leq 3$
$\frac{\pi \left(- 4 D_{e}^{2} + Di_{d}^{2}\right)}{4}$$N_{c} > 3$
Related
$D_{e}$
Used in
$Q_{d_{fill}}$