The hydraulic diameter, DH, is a commonly used term when handling flow in noncircular tubes and channels. Using this term one can calculate many things in the same way as for a round tube. It is defined as
Hydraulic diameter is mainly used for calculations involving turbulent flow. Secondary flows can be observed in non-circular ducts as a result of turbulent shear stress in the turbulent flow. When the flow is laminar, secondary flows do not occur.
Hydraulic diameter is also used in calculation of heat transfer in internal flow problems.
List of Hydraulic Diameters
|Circular Tube||For a circular tube the hydraulic diameter is simply the diameter of the tube.|
|Rectangular Duct (Fully filled)|
|Channel of water or partial filled rectangular duct||For the limiting case of a very wide duct, i.e. a slot of width a where a ≫ b, then DH = 2b|