Laminar Flow
Laminar flow is a smooth, orderly regime of fluid motion in which fluid particles travel in parallel layers (laminae) without lateral mixing or cross-current fluctuations. It occurs at low Reynolds numbers (typically Re < 2300 in pipes) where viscous forces dominate over inertial forces, producing a parabolic velocity profile in pipe flow. Laminar flow is essential in microfluidics, blood flow in capillaries, lubrication engineering, and precision chemical dosing.
Comparison of Laminar Flow Properties in Circular Pipes
| Property | Laminar Flow | Turbulent Flow | Engineering Impact |
|---|---|---|---|
| Reynolds number range | Re < 2300 | Re > 4000 | Determines pump sizing |
| Velocity profile | Parabolic | Nearly flat (plug) | Affects mixing and heat transfer |
| Friction factor (Darcy) | f = 64/Re | Moody chart dependent | Pressure drop calculation |
| Energy dissipation | Low | High | Pipe efficiency |
| Mixing | Negligible (diffusion only) | Vigorous | Chemical reactor design |
| Typical application | Capillary tubes, blood vessels | Ventilation ducts, rivers | System design |
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Related Terms
Turbulent Flow
Turbulent flow is a chaotic, irregular fluid motion characterised by rapid fluctuations in velocity and pressure, eddies, vortices, and vigorous lateral mixing between fluid layers. It occurs when inertial forces overcome viscous forces, typically at Reynolds numbers above 4000 in pipe flow, and is the dominant regime in most industrial, atmospheric, and oceanic flows. Despite its complexity, turbulent flow enhances heat and mass transfer, making it beneficial in heat exchangers and combustion systems.
Reynolds Number
The Reynolds number (Re) is a dimensionless quantity that predicts the flow regime of a fluid by comparing inertial forces to viscous forces within the flow. A low Reynolds number indicates that viscous forces dominate, resulting in smooth laminar flow, while a high value signals that inertial forces dominate, leading to turbulent flow. It is indispensable in scaling model experiments to full-size systems, designing pipelines, and predicting aerodynamic behaviour around aircraft and vehicles.
Viscosity
Viscosity is a measure of a fluid's resistance to deformation or flow under an applied shear stress, arising from internal friction between adjacent fluid layers moving at different velocities. Dynamic (absolute) viscosity quantifies the shear stress needed to produce a unit velocity gradient, while kinematic viscosity is the ratio of dynamic viscosity to fluid density. Viscosity governs flow behaviour in lubrication, blood circulation, polymer processing, and aerodynamics.
From Latin "lamina" (a thin plate or layer). The term "laminar" entered fluid mechanics in the 19th century, popularised by Osborne Reynolds following his landmark 1883 experiments distinguishing smooth from chaotic flow regimes.