Hydraulic diameter expresses the area-to-wetted-perimeter ratio as a length.
Difficulty
Intermediate
Read time
4 min
Prerequisites
Consistent SI units, algebra, and the physical assumptions listed below
Source
Teng-Jui Lin — Equation SheetsAdapted from Teng-Jui Lin, Equation Sheets — Mechanical Engineering, under CC BY 4.0.
Adapted notation and added original explanations, variables, assumptions, applications, and a worked example. Used D_h = 4 R_H from the source's hydraulic radius and noncircular-pipe Reynolds-number definitions.
Hydraulic diameter expresses the area-to-wetted-perimeter ratio as a length. It allows some internal-flow quantities to be written in a pipe-like form, but a hydraulic-diameter substitution does not make every circular-pipe correlation valid for every duct.
| Symbol | Meaning | Units |
|---|---|---|
| Hydraulic diameter | ||
| Flow cross-sectional area | ||
| Wetted perimeter |
Provide a characteristic length for a suitable internal-flow model.
Compare cross-section geometry using area and wetted perimeter.
A full rectangular duct is 0.20 m wide and 0.10 m high. Find its hydraulic diameter.
Adapted from Teng-Jui Lin, Equation Sheets — Mechanical Engineering, under CC BY 4.0.
Adapted notation and added original explanations, variables, assumptions, applications, and a worked example. Used D_h = 4 R_H from the source's hydraulic radius and noncircular-pipe Reynolds-number definitions.
Assumptions
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