folyássebesség

folyássebesség, also called flow velocity, refers to the speed at which a fluid—liquid or gas—moves through a given section of a flow path. It is defined as the rate of change of the fluid's displacement with respect to time, and is typically expressed in metres per second (m/s), centimetres per second (cm/s), or litres per minute (L/min) for liquids, and in centimetres per second or inches per second for gases. The value of a flow velocity depends on the fluid’s momentum, the cross‑sectional area of the conduit or channel, and the forces acting on the fluid, such as pressure gradients, gravity, or external pumps and fans.

In engineering applications, the flow velocity is a key parameter for determining shear stress on pipe walls, the Reynolds number for characterising laminar or turbulent flow, and the capacity of pumps and turbines. Accurate measurement of flow velocity is essential for validating hydraulic models, designing efficient piping systems, and monitoring environmental flows in rivers and atmospheric currents. Common measurement techniques include pitot‑tube manometers, electromagnetic flow meters, ultrasonic transit‑time meters, and tracer‑gas methods. Each technique has advantages and limitations with respect to flow regime, fluid conductivity, temperature, and pipe material. Therefore the choice of measurement method is influenced by the required accuracy, operating conditions, and the fluid’s physical properties.

In summary, the folyássebesség is a fundamental hydrodynamic quantity that quantifies how fast a fluid traverses a given cross‑section. It is indispensable in various fields such as civil engineering, environmental science, petroleum engineering, and meteorology, where it underpins the design, analysis, and monitoring of fluid systems.