Model smooth, steady motion for low-speed fluids inside. Choose units, save datasets, and verify assumptions. See results instantly above the form after submission here.
| Fluid | ρ (kg/m³) | μ (Pa·s) | D (m) | L (m) | V (m/s) | Q (m³/s) | ΔP (Pa) | Re | f | h (m) |
|---|---|---|---|---|---|---|---|---|---|---|
| Water (reference case) | 998 | 0.001 | 0.02 | 10 | 0.5 | 1.5708e-4 | 400 | 998 | 0.006413 | 0.04087 |
Laminar behavior in a round pipe is controlled by the Reynolds number, Re equals rho times V times D divided by mu. A common limit is Re below 2300. With water at 20 C, rho about 998 kilograms per cubic meter and mu about 0.001 pascal seconds, a diameter of 0.02 meters gives Re about 1996 at V 0.10 meters per second.
Viscosity changes can dominate the result. Water near 10 C is roughly 0.00131 pascal seconds, while near 30 C it is about 0.00080 pascal seconds, so Re can shift by about thirty percent at the same V and D. If you enter kinematic viscosity nu, the conversion uses mu equals nu times rho. For water at 20 C, nu is about 1.004 centistokes.
For laminar flow, the pressure drop follows delta P equals 32 mu L V divided by D squared. Doubling the pipe length doubles delta P, while doubling the diameter reduces delta P by a factor of four. The flow form is Q equals pi D to the fourth times delta P divided by 128 mu L. Using mu 0.001, L 10, D 0.02, and V 0.50 gives delta P about 400 pascals and Q about 9.42 liters per minute.
The Darcy friction factor in laminar flow is f equals 64 divided by Re. Head loss is h equals delta P divided by rho g; with delta P 400 and rho 998, h is about 0.041 meters of fluid. Wall shear stress is tau w equals delta P D divided by 4 L; the same case gives about 0.20 pascals for surface comparisons.
Use the consistency check delta P equals f times L over D times rho V squared over 2 to confirm units. A laminar ceiling is V max equals Re crit mu divided by rho D; with Re crit 2300, V max is about 0.115 meters per second and Q max about 2.17 liters per minute. Store multiple runs to compare diameter changes and operating targets quickly. Export results to keep assumptions transparent.
It assumes a Newtonian fluid in steady, fully developed pipe flow. Density and viscosity are treated as constants, so strong compressibility, rapid heating, or shear thinning can make results less accurate.
A common engineering threshold is 2300 for internal pipe flow. If you need a conservative check, use a lower value such as 2000. For specialized setups, set the critical value to match your reference.
One uses the laminar Poiseuille relation, while the other uses Darcy–Weisbach with f equals 64 divided by Re. In true laminar conditions they should be very close; differences usually come from rounding and unit conversions.
Use dynamic viscosity when you have pascal second or centipoise data. Use kinematic viscosity when you have centistokes data, and the calculator converts it using mu equals nu times rho. Make sure density matches the same temperature.
No. It models straight pipe friction only. If you have fittings, add minor loss terms using K values and the velocity head, or increase the effective length. For detailed networks, use a dedicated piping model.
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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.