Pipe Flow Calculator | Flow Rate, Velocity, Reynolds Number

📖 How to Use This Pipe Flow Calculator

Enter pipe diameter (D) – The internal diameter of the pipe in millimeters.

Enter pressure drop (ΔP) – The pressure difference between pipe ends in kPa.

Enter pipe length (L) – The total length of the pipe in meters.

Select fluid type – Choose from common fluids or enter custom properties.

Use presets or custom – Click presets for typical pipe sizes or enter your own values.

🌊 Understanding Pipe Flow

Pipe flow analysis is essential for designing piping systems, pumps, and fluid transport systems. The flow rate, velocity, and Reynolds number help determine the flow regime and pressure losses.

This calculator uses the Hagen-Poiseuille equation for laminar flow:

Q = (π × ΔP × D⁴) / (128 × μ × L)
v = Q / A (where A = πD²/4)
Re = ρ × v × D / μ
where Q = flow rate, ΔP = pressure drop, D = pipe diameter, μ = viscosity, L = pipe length, ρ = density, v = velocity.

For turbulent flow (Re > 2300), the Darcy-Weisbach equation with friction factor is used in practice.

💡 Practical Applications

Water supply systems – Municipal water distribution, irrigation.
Industrial piping – Chemical plants, refineries, and manufacturing.
HVAC systems – Chilled water, condenser water, and air ducts.
Oil & gas – Pipeline transport, wellhead flow lines.
Hydraulic systems – Fluid power transmission lines.

❓ Frequently Asked Questions (FAQ)

What is the Reynolds number and why is it important?

The Reynolds number (Re) determines the flow regime: Re < 2300 is laminar, Re > 4000 is turbulent, and between 2300-4000 is transitional. It's critical for calculating friction factors and pressure losses.

What is the difference between laminar and turbulent flow?

Laminar flow is smooth and orderly, with layers of fluid sliding past each other. Turbulent flow is chaotic and mixed, with eddies and vortices. Turbulent flow has higher pressure losses.

What fluids can I use with this calculator?

You can use water, air, oil, glycerin, or any custom fluid by entering its density and viscosity. The calculator assumes Newtonian fluids.

What is the effect of pipe roughness?

This calculator assumes smooth pipes (laminar flow). For turbulent flow, pipe roughness significantly affects the friction factor and pressure drop. Use the Darcy-Weisbach equation with a friction factor for turbulent flow.

Can I use this for gases?

Yes, for incompressible flow at low pressure drops. For high pressure drops or large pressure changes, compressible flow equations are needed.

What is the Hagen-Poiseuille equation?

It's a fundamental equation for laminar flow in a circular pipe. It relates flow rate to pressure drop, pipe geometry, and fluid viscosity. It assumes fully developed laminar flow in a smooth pipe.