Calculator
Example data
These rows show typical inputs and representative outputs.
| Mode | Fluid | ρ (kg/m³) | μ (Pa·s) | D (m) | L (m) | ε (m) | Q (m³/s) | V (m/s) | Re | f | hL (m) | ΔP (kPa) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Friction losses | Water | 998 | 0.001 | 0.05 | 30 | 0.000045 | 0.004 | 2.037 | 1.017e5 | 0.0220 | 2.79 | 27.3 |
| Bernoulli | Water | 998 | 0.001 | 0.05 | 30 | 0.000045 | 0.004 | |||||
| Pump power | Water | 998 | 0.004 |
Formulas used
How to use this calculator
- Pick a calculation mode that matches your question.
- Enter fluid properties, then provide geometry and flow data.
- Add roughness and K values to model fittings.
- Press Calculate to see results above.
- Use the export buttons for CSV or PDF files.
Engineering assumptions for incompressible models
This calculator targets steady, single‑phase liquids where density changes are negligible. It treats the pipe section as fully filled and uses average velocity across the cross‑section. If the flow contains air pockets, flashing, cavitation, or large temperature gradients, results can deviate. Use measured properties when possible, especially for oils and glycol mixes. Gravity is fixed at standard g to keep head calculations consistent across modes.
Input strategy and unit discipline
Enter diameter as internal diameter, not nominal. For flow rate, choose a unit that matches your instrumentation and keep values realistic for the pipe size. Viscosity may be entered in Pa·s or cP, while pressures accept common engineering units. Elevations are optional but become important for vertical runs. When a field is not required for the selected mode, it is hidden to reduce input noise and mistakes.
Reynolds number and friction factor interpretation
Reynolds number separates laminar and turbulent behavior through Re = ρVD/μ. In laminar flow, the friction factor follows f = 64/Re and is highly sensitive to viscosity. For turbulent flow, the tool uses a robust explicit approximation based on roughness and Reynolds number. Roughness matters most in the fully rough regime; in smoother pipes at moderate Re, friction is dominated by inertia and only weakly by ε.
Loss modeling for systems and fittings
Major losses are computed with Darcy–Weisbach, hf = f(L/D)(V²/2g). Minor losses represent fittings, valves, entrances, and expansions using hm = K(V²/2g). The calculator reports head loss and converts it to pressure drop with ΔP = ρghL. For Bernoulli mode, losses can be included using average velocity, producing a practical downstream pressure estimate for quick system checks. Validate diameter, roughness, and K inputs.
Export workflows and verification practices
After calculation, export results as CSV for spreadsheets or as a compact PDF for design notes. Treat outputs as first‑pass estimates: confirm diameters, check that velocities remain within erosion and noise limits, and validate pressure drops against pump curves. When sizing, iterate between target velocity and acceptable head loss. For commissioning, compare measured differential pressure with predicted values to refine K and roughness assumptions.
FAQs
Which friction factor method is applied?
Laminar flow uses f = 64/Re. Turbulent flow uses an explicit Swamee–Jain approximation with ε and D. This provides stable estimates without iterative solvers, suitable for preliminary design and comparisons.
Can I calculate velocity from a measured flow rate?
Yes. Select “Velocity from flow rate,” enter diameter and flow, and the tool computes V from V = Q/A. It also reports mass flow, dynamic pressure, and Reynolds number when fluid properties are provided.
How do I include valves and bends?
Add their loss coefficients to a single K value. Use vendor tables or handbooks, then sum K for every fitting in the run. The calculator converts K into minor head loss hm = K(V²/2g).
Is this valid for compressible gases?
Not generally. The equations assume density is nearly constant. For gas systems with large pressure changes, use compressible flow methods and include real‑gas effects when needed. You may still use it for very low Mach, small ΔP cases.
Why are exports sometimes unavailable?
Exports require a successful calculation. If required inputs are missing or non‑numeric, the tool blocks the download and lists errors. Re‑run the calculation, then use the buttons to generate CSV or PDF outputs.
What target velocity should I pick for sizing?
Choose a velocity based on noise, erosion, and energy cost. For many water services, 1–3 m/s is common. After sizing, review head loss and iterate until both velocity and pressure drop meet your criteria.