ChemCalc's pipe module calculates single-phase pressure drop using the Darcy-Weisbach equation with the Swamee-Jain explicit approximation of the Colebrook-White equation — accurate to ±3% across all turbulent regimes without iteration.
Inputs
| Parameter | Notes |
|---|---|
| Flow rate (kg/h or m³/h) | Mass or volumetric flow |
| Pipe ID (mm) | Internal diameter; schedule lookup from B36.10M built-in table |
| Pipe length (m) | Straight pipe length |
| Absolute roughness ε (mm) | Default 0.046 mm (commercial steel); 0.0015 mm (smooth) |
| Fluid density ρ (kg/m³) | Liquid or gas at operating conditions |
| Dynamic viscosity μ (Pa·s) | At operating temperature |
| Fittings (optional) | Equivalent length method — gate valve, elbow, tee, reducer, etc. |
Outputs
- ΔP (kPa) — total pressure drop including fittings
- Velocity (m/s) — average flow velocity
- Reynolds number Re — flow regime indicator
- Friction factor f — Darcy (Moody) friction factor
- Pipe wall thickness — ASME B31.3 / GB/T 20801 t_min from schedule lookup
Friction Factor Formula
For laminar flow (Re < 2300): f = 64/Re. For turbulent flow, ChemCalc uses the Swamee-Jain (1976) explicit approximation of Colebrook-White:
f = 0.25 / [log₁₀(ε/3.7D + 5.74/Re⁰·⁹)]²
| Flow Regime | Re Range | f behavior |
|---|---|---|
| Laminar | Re < 2300 | f = 64/Re |
| Turbulent smooth | Re > 4000, small ε/D | Approaches Blasius / Prandtl-Kármán |
| Fully rough | Re > 4000, large ε/D | f → const (ε/D only) |
Pipe Schedule Reference (ASME B36.10M)
ChemCalc includes the full B36.10M schedule table for NPS ½ to 24 (DN 15–600): STD, XS, 160, XXS schedules with wall thicknesses. The pipe wall module computes t_min per ASME B31.3 (process piping) or GB/T 20801 from design pressure, material allowable stress, weld quality factor E_w, and mill tolerance.
Two-Phase Pressure Drop
For gas-liquid two-phase flow, ChemCalc uses the Lockhart-Martinelli (1949) method with Chisholm (1967) parameter C, computing the two-phase multiplier φ² from individual gas and liquid single-phase pressure drops. Outputs include the Martinelli parameter X and the recommended C factor.