General engineering arithmetic — not an ISO pipe selector
Circular-Pipe Flow–Area Arithmetic
Relate actual volumetric flow, cross-sectional mean velocity and actual circular inside diameter at one documented operating state. The worksheet does not invent a standard pipe size or design velocity.
Q is actual volumetric flow at the assessed state [m³/s], A is the full circular internal flow area [m²], d is actual internal flow diameter [m], and v̄ is area-average velocity normal to that cross-section [m/s]. The equations are dimensional geometry and general engineering flow arithmetic; they are not presented as an ISO sizing formula.
Exact conversion basis
1 L=10−3 m³; 1 h=3600 s; 1 min=60 s; 1 in=0.0254 m exactly; 1 ft=0.3048 m exactly; and 1 US gallon=231 in³=0.003785411784 m³ exactly. “US gal/min” is explicitly not an Imperial gallon.
No automatic pipe selection
ISO 6708:1995 defines the DN alphanumeric designation system; it does not make DN equal to actual ID. NPS, outside diameter, schedule/wall series, material, manufacturing tolerance, lining, corrosion allowance and temperature/pressure effects are separate product-design inputs.
Not calculated
- Pressure drop, pump duty, Reynolds number, roughness, fittings or elevation effects.
- Cavitation, flashing, compressibility changes, two-phase flow, erosion, water hammer, surge or acoustic/noise response.
- Economic or safe velocity, minimum wall, pressure rating, corrosion/erosion allowance or code compliance.
- Whether a selected nominal product has sufficient minimum ID after tolerances and service allowances.
Bronnen
University of Dayton, Volumetric Flowrate, Velocity and the Continuity Equation (2022); NIST SI Units — Length; NIST Handbook 44 Appendix C conversion table; ISO 6708:1995.
