Friction Loss Calculator
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Other tools you may find usefulFriction loss calculator in pipelines – Darcy–Weisbach, Colebrook–White, Hazen–Williams
Calculate the pressure drop in pipelines for water, glycol and other liquids: using theDarcy–Weisbach method(with linear and local friction), as well as empiricallyHazen–Williams. The tool calculates theReynolds number, friction coefficient f(including the Colebrook–White equation), takes into account therelative roughness k/D, of the fitting by the K coefficientsorequivalent lengths, and gives the result asΔp[Pa/kPa/bar] andhead drop hf[m] – together withrequired pump head.
Run the friction loss calculator Formulas, tables and examples
Calculation range
- Linear friction:Δplinand hfby the Darcy–Weisbach method for internal diameter, flow and viscosity.
- Local friction:elbows, valves, tees – throughKorequivalent length Leq.
- Reynolds and regimes:laminar, transient, turbulent; model selection forf.
- Colebrook–White / Swamee–Jain:calculation offfrom k/D without iteration or iteratively.
- Hazen–Williams:quick estimates for cold water (parameterC).
- Units and conversions:m, mm, L/s, m³/h, GPM; Pa, kPa, bar; m H2O.
- Pump:head H = (Δptotal/ ρg) + reserves.
Key formulas
Q – flow, v – average velocity, D – internal diameter, ρ – density, μ – dynamic viscosity.
f – Darcy friction coefficient, K – local coefficients (fittings, fittings), L – length.
Friction coefficient f
Laminar (Re < 2300)
In this range, the result depends only on viscosity and flow – roughness does not matter
Turbulent (Re >~ 4000)
Colebrook–White equation – usually solved iteratively. Non-iterative approximation: Swamee–Jain.
Hazen–Williams (for water, estimation)
D [m], Q [m³/s], L [m];C– coefficient (e.g. 140 for smooth pipes). Method for water at ~5–25°C.
Roughness and typical k values
| Pipe material | k – roughness [mm] | Comments |
|---|---|---|
| PE/PVC smooth | 0.001–0.01 | Low resistance, large C |
| Copper | 0.001–0.015 | Very smooth |
| New steel | 0.03–0.1 | k increases over time |
| Galvanized steel | 0.1–0.2 | Older installations – higher k |
| Cast iron | 0.2–0.5 | Municipal pipelines |
| Concrete | 0.3–3.0 | Large diameters, channels |
Local losses - K coefficients and equivalent lengths
Model K
Each element (elbow, valve, tee) has a coefficientK. The sumΣKcounts the local hf= ΣK·v²/(2g).
Equivalent length Leq
Replaces the element with a pipe segment: Leq= (K·D)/f. The sum of L + ΣLeqgives the effective length for linear friction.
Calculation examples
Example A – water, D=50 mm, L=80 m
Q = 8 m³/h = 0.00222 m³/s. D = 0.05 m ⇒ v = 4Q/(πD²) ≈ 1.13 m/s.
Assume k = 0.05 mm ⇒ k/D = 0.001. Re at 20°C (ρ≈998, μ≈1e−3): Re ≈ 56,500 ⇒ turbulent flow.
Swamee–Jain ⇒ f ≈ 0.020. hf,lin= f·(L/D)·v²/(2g) ≈ 0.020·(80/0.05)·1.13²/(2·9.81) ≈ 2.08 m.
Fittings: 2 × elbow K=0.9; 1 × ball valve K=0.05 ⇒ ΣK = 1.85 ⇒ hf,have≈ 1.85·1.13²/(2·9.81) ≈ 0.12 m.
Total: hf≈ 2.20 m ⇒ Δp ≈ 998·9.81·2.20 ≈ 21.5 kPa ≈ 0.215 bar.
Example B – Hazen–Williams, C=140
The same L and D, Q=8 m³/h. For SI: hf= 10.67·L·Q¹·⁸⁵²/(C¹·⁸⁵²·D⁴·⁸⁷).
Approximate result ~2.1–2.3 m (close to Darcy–Weisbach). Differences depend on C and the scope of applicability.
Example C – influence of diameter
Q = 8 m³/h; change D from 50 mm to 65 mm: v decreases, hfdecreases non-linearly (approx. 40–60%). Larger diameter – lower losses, higher cost.
Example D – glycol 30%
Higher viscosity ⇒ lower Re ⇒ higherfand higher hf. In refrigeration and HVAC, it often determines the selection of the pump.
Required pump lifting height
hstat– level difference between suction and discharge. Reserves take into account dirt, installation aging and tolerances.
Units and conversions
| Quantity | Units | Conversions |
|---|---|---|
| Flow Q | m³/h, m³/s, L/s, L/min, GPM | 1 m³/h = 0.2778 L/s = 16.667 L/min |
| Pressure Δp | Pa, kPa, bar | 1 bar = 100 kPa = 10⁵ Pa |
| Height h | m H₂O | Δp [Pa] = ρ g h ⇒ for water ~ 9.81 kPa/m |
| Diameter D | mm, m | mm → m: divide by 1000 |
| Viscosity μ | Pa s | 1 mPa s = 0.001 Pa s |
FAQ
When to use Hazen–Williams?
For quick estimates for water at typical temperatures in smooth pipes. For accurate calculations and other liquids – Darcy–Weisbach.
How to select roughness k?
Select from material tables; for aging installations, adopt a larger k or add a reserve.
Does K for fittings depend on diameter?
Yes, K values are usually published for the Re range and geometry; for large changes in diameter, use the manufacturer's data or Leq.
Re laminar result - what about f?
For Re < 2300 use f = 64/Re. Do not use Colebrook - it does not apply to laminar flow.
How to account for a cascade of episodes?
Sum hfof all segments and elements: linear + local. Finally, convert to Δp and H for the pump.
Design checklist
Inputs
- Q or v, Dint, L, material (k), temperature (μ, ρ).
- Armature: K or L listeq.
- Assumptions for H: hstat, reserves.
Results
- Re, f, v.
- hf,lin, hf,have, Δp.
- H pumps and conversions (kPa, bar, m).
Summary:The Darcy–Weisbach method with the correct selection off(Colebrook–White or Swamee–Jain), taking into account roughness and local losses K, gives reliable results for most process liquids and water. Hazen–Williams is useful for quick estimates. Ultimately, based on the total pressure drop and level difference, you will easily determine the required pump head.