# Hydraulic diameter of circular duct

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Anastase.Hydraulic diameter of circular duct
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The Hydraulic Diameter of a Circular Duct calculator computes the hydraulic diameter of a circular duct based on the radius (r) of the duct.

INSTRUCTION: Choose units and enter the following:

• (r) This is the radius of the duct.

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

#### The Math / Science

Hydraulic diameter of circular duct

dh = 2•r

where:

A hydraulic diameter is useful for dimensionless quantities (e.g.  Reynolds number or Gauckler-Manning Equation) 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.