อัปเดต 2026-09-07

Pressure drop

Darcy–Weisbach

Computes frictional + minor-loss pressure drop across a straight pipe run from velocity, diameter, roughness, viscosity and density (velocity.ts pipePressureDrop).

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Darcy–Weisbach friction term plus a ΣK minor-loss term, both driven off one Darcy friction factor: laminar 64/Re below Re=2000, Swamee–Jain (explicit Colebrook approximation) above Re=4000, with a smooth cubic-Hermite blend across the 2000–4000 transition band so the head-loss curve has no visible step.

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Darcy–Weisbach pressure drop

Δ P = f \frac{L}{D} \cdot \frac{1}{2} ρ v^{2} + Σ K \cdot \frac{1}{2} ρ v^{2}

f = Darcy friction factor, L/D = length/diameter, ½ρv² = velocity pressure, ΣK = summed fitting loss coefficients

Reynolds number

R e = \frac{v D}{ν}

v = bulk velocity (m/s), D = inner diameter (m), ν = kinematic viscosity (m²/s)

Friction factor (Swamee–Jain, turbulent)

f = \frac{0.25}{[ lo g _{10} ( \frac{ε}{3.7 D} + \frac{5.74}{R e ^{0.9}} ) ] ^{2}}

explicit approximation to Colebrook; laminar branch below Re=2000 is f=64/Re

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