Hydraulic diameter

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The hydraulic diameter, D_H, is a commonly used term when handling flow in non-circular tubes and channels. Using this term, one can calculate many things in the same way as for a round tube. It is defined as

${\displaystyle D_{\text{H}}={\frac {4A}{P}},}$

where

${\displaystyle A}$ is the cross-sectional area,

${\displaystyle P}$ is the wetted perimeter of the cross-section.

The need for the hydraulic diameter arises due to the use of a single dimension in case of dimensionless quantity such as Reynolds number, which prefer a single variable for flow analysis rather than the set of variables as listed in the table. The Manning formula contains a quantity called the hydraulic radius. Despite what the name may suggest, the hydraulic diameter is not twice the hydraulic radius, but four times larger.

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.

Video Hydraulic diameter

List of hydraulic diameters

For a fully filled duct or pipe whose cross-section is a regular polygon, the hydraulic diameter is equivalent to the diameter of a circle inscribed within the wetted perimeter.

Maps Hydraulic diameter

References

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See also

• Equivalent spherical diameter
• Hydraulic radius
• Darcy friction factor

Source of article : Wikipedia