The hydraulic diameter is a term used in fluid mechanics and thermodynamics. It is a measure of the efficiency of a section to pass flow by relating the cross-sectional area of flow to the wetted perimeter of the cross-section.
The hydraulic diameter of a round pipe is simply its diameter. The equations for hydraulic diameter for other cross-sections are given in the table below.
Flowing Full | |
---|---|
Circle | |
Annulus | |
Square (L = side) | |
Rectangle (L_{1} and L_{2 }= sides) | |
Flowing partially full | |
Half-filled circle (d = diameter) | |
Rectangle (h = height, w = width) | |
Wide, shallow stream (d = depth) | |
Triangle (d = depth, t = top, s = side length) | |
Trapezoid (d = depth, t = top, b = bottom, s = side length) |
The hydraulic diameter should not to be confused with the hydraulic radius term in the Manning equation, which is not half of the hydraulic diameter, but rather one quarter.
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