Hydraulic Diameter Calculator
Compute the hydraulic diameter of a rectangular duct or non-circular conduit for fluid flow analysis.
Hydraulic Diameter
342.9 mm
Hydraulic Diameter vs Duct Width (a)
Formule
## Hydraulic Diameter The hydraulic diameter allows non-circular conduits to be analysed using the same formulas developed for circular pipes. ### Formula **D_h = 4 A / P** where A is the cross-sectional flow area and P is the wetted perimeter. For a rectangular duct with sides a and b: D_h = 4ab / (2(a+b)) = 2ab / (a+b). For a circle, D_h equals the actual diameter.
Exemple Résolu
A rectangular HVAC duct 400 mm wide and 300 mm tall.
- 01Area = 400 x 300 = 120,000 mm^2
- 02Perimeter = 2 x (400 + 300) = 1,400 mm
- 03D_h = 4 x 120,000 / 1,400 = 342.9 mm
Questions Fréquentes
Why not just use the average of width and height?
The hydraulic diameter accounts for the relationship between flow area and wall friction area (wetted perimeter). A simple average would not correctly represent the friction behaviour.
What is hydraulic diameter for a square duct?
For a square duct with side s, D_h = 4s^2 / (4s) = s. The hydraulic diameter equals the side length.
When is hydraulic diameter used?
Use it for computing Reynolds number, friction factor, and head loss in non-circular conduits: HVAC ducts, open channels, annular spaces, and non-standard piping cross-sections.
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