Duct Exit Head Loss
Calculates the head-loss coefficient and pressure drop for an abrupt pipe or duct exit into a large receiving space (plenum or atmosphere).
Loss Coefficient
For an abrupt (sudden expansion) exit, all of the kinetic energy of the flow is dissipated by turbulent mixing in the receiving space:
K=1.0Pressure Drop
Δp=K⋅21ρV2=21ρV2where ρ is the air density and V is the mean flow velocity in the duct at the exit plane.
Physical Interpretation
The Borda–Carnot (sudden-expansion) theorem gives K=(1−A1/A2)2. When the receiving space is much larger than the duct (A1/A2→0), this reduces to K=1.0, meaning the entire dynamic head is lost.
References
- Idel'chik, I.E. and Fried, E., Flow Resistance, a Design Guide for Engineers, Taylor & Francis, Washington D.C., 1989, p. 349.