Reynolds Number Calculator

Reynolds number (Re) is a dimensionless quantity that predicts flow patterns in fluid flow situations. It is defined as the ratio of inertial forces to viscous forces and is used to determine whether flow is laminar (smooth) or turbulent (chaotic).

For pipe flow, Re < 2,300 indicates laminar flow, 2,300 ≤ Re < 4,000 is transitional, and Re ≥ 4,000 indicates turbulent flow. Most industrial pipe flows are turbulent.

Reynolds number is calculated as Re = (ρ × V × D) / μ or Re = (V × D) / ν, where ρ is fluid density, V is velocity, D is pipe diameter, μ is dynamic viscosity, and ν is kinematic viscosity.

Reynolds number determines which equations and correlations to use for pressure drop, heat transfer, and mass transfer calculations. It's fundamental for designing pipes, pumps, heat exchangers, and other process equipment.

Reynolds number increases with higher velocity, larger pipe diameter, higher fluid density, or lower viscosity. Temperature affects viscosity significantly - heating a liquid reduces its viscosity and increases Re.

For water flowing at 2 m/s in a 50mm pipe at 20°C, Re ≈ 100,000 (turbulent). Most water systems operate in the turbulent regime because water has low viscosity.