Reynolds Number Calculator
The Reynolds number (Re) is a dimensionless quantity that predicts whether fluid flow will be laminar or turbulent. It is defined as Re = vL/nu, where v is flow velocity, L is a characteristic length (such as pipe diameter), and nu is kinematic viscosity. This calculator computes Re and classifies the flow regime.
The Reynolds number represents the ratio of inertial forces to viscous forces in a fluid. Low Re (below 2300 for pipe flow) indicates laminar flow, with smooth, orderly layers of fluid sliding past each other. High Re (above 4000) indicates turbulent flow, with chaotic, swirling motion with eddies and mixing. The range 2300-4000 is the transitional zone where flow can switch between regimes.
The characteristic length depends on the geometry: for pipe flow, it is the internal diameter; for flow over a flat plate, it is the distance from the leading edge; for a sphere, it is the diameter. The kinematic viscosity ν = μ/ρ depends on the fluid and temperature.
Reynolds number is critical in engineering design. Laminar flow has lower friction losses but poor mixing. Turbulent flow has higher drag but better heat and mass transfer. Pipe sizing, pump selection, heat exchanger design, and aerodynamic analysis all rely on Reynolds number calculations.