MihsabaHow to use
Hagen-Poiseuille flow describes steady laminar motion of a Newtonian fluid in a long circular tube. Flow is extremely sensitive to radius because Q scales with r⁴.
- Enter pressure difference.
- Enter inside radius and tube length.
- Enter dynamic viscosity and density.
- Review Q, mean speed and Reynolds number.
How it is calculated
Q=πr⁴ΔP/(8μL)
Example
With ΔP=1000 Pa, r=1 mm, μ=0.001 Pa·s and L=1 m, Q is about 0.393 mL/s.
Important notes
If Reynolds number is high, the laminar premise may fail. Non-Newtonian fluids require a different model.
Frequently asked questions
Radius or diameter?
Enter inside radius r; substituting diameter causes a large error because r is raised to the fourth power.
Why is density requested?
It is not needed for Q itself; it is used here for Reynolds number.
When should I avoid this law?
For non-laminar flow, non-Newtonian fluids or geometry that violates fully developed tube-flow assumptions.