Hydraulic Diameter of a Rectangular Duct (fully filled)

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Equation / Last modified by KurtHeckman on 2018/03/19 18:31
AndrewS.Hydraulic Diameter of a Rectangular Duct (fully filled)

The Hydraulic Diameter of a fully filled Rectangular Duct calculator compute the hydraulic diameter of a fully filled rectangular duct based on its dimensions.

INSTRUCTIONS: Choose units and enter the following:

  • (a) This is the width of the rectangular duct.
  • (b) This is the height of the rectangular duct.

Hydraulic Diameter (DH): The calculator returns the diameter in meters.  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The formula for the Hydraulic Diameter of a Rectangular Duct (fully filled)  is:

`D_H = (4*a*b)/(2*(a+b))`


A hydraulic diameter is useful for dimensionless quantities (e.g.  Reynolds number) which employ a single variable for flow analysis.

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. Hydraulic diameter is also used in calculation of heat transfer in internal-flow problems.