Pipe Flow Reynolds Number and Regime
The dimensionless ratio behind every friction-factor decision, which the friction tiles use implicitly but never show: Re = V D / nu sorts pipe flow into laminar (Re < 2,300), transitional, and turbulent (Re > 4,000). 60 F water at 6 ft/s in a 2 in line runs Re 82,600 - firmly turbulent, as nearly all trade piping is, which is why the Hazen-Williams and Colebrook forms apply; slow it to a crawl and Re 275 laminar, where f = 64/Re and loss is linear in velocity. Enter the kinematic viscosity for the fluid and temperature. An engineering aid; the fluid property data govern.
Formula and source
Re = V (D/12) / nu; regime = Re < 2,300 laminar, <= 4,000 transitional, else turbulent.
The Reynolds number Re = V D / nu (= rho V D / mu) and the standard pipe-flow transition bands, with a 60 degF water kinematic viscosity of about 1.21e-5 ft^2/s, a standard fluid-mechanics result, by name.
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