Laminar, Transitional and Turbulent Flow

Heat transfer, pressure and head loss in a fluid varies with laminar, transitional or turbulent flow.

Overview

There are three main types of fluid flow in pipes:

Laminar Flow: Occurs with small pipes and low flow velocities. Flow behaves like concentric cylinders, with shear stress dependent on viscosity.
Turbulent Flow: Occurs at high flow rates with larger pipes. Vortices and eddies make flow unpredictable. Shear stress depends on density.
Transitional Flow: A mixture of laminar and turbulent flow, occurring between the two.

The flow type is determined by the dimensionless Reynolds Number:

Flow Type	Reynolds Number Range	Characteristics	Shear Stress Dependency
Laminar	Re < 2,300	Small pipes, low velocities, concentric cylinder flow	Viscosity (μ)
Transitional	2,300 ≤ Re ≤ 4,000	Mixture of laminar and turbulent, turbulence in center	Viscosity & Density
Turbulent	Re > 4,000	Large pipes, high velocities, vortices and eddies	Density (ρ)

Flow Type

Reynolds Number Range

Characteristics

Shear Stress Dependency

Laminar

Re < 2,300

Small pipes, low velocities, concentric cylinder flow

Viscosity (μ)

Transitional

2,300 ≤ Re ≤ 4,000

Mixture of laminar and turbulent, turbulence in center

Viscosity & Density

Turbulent

Re > 4,000

Large pipes, high velocities, vortices and eddies

Density (ρ)