# Physical principles of the measurement parameter flow velocity

Flow is a directional movement of particles or continuous media. There is water flow or gas flow flow, for example. The SI unit for flow velocity is metres per second (m/s).

Depending on the occurrence of turbulence, one differentiates between laminar flow (without turbulence) and turbulent flow (with turbulence).

## Flow in a duct

#### Laminar flow

• From lat. "turbulentus": unruly, turbulent
• Motion of liquids and gases in which turbulences of all size scales occur
• Usually three-dimensional, apprarently random, non-stationary movements of fluid particles

#### Turbulent flow

• From lat. "turbulentus": unruly, turbulent
• Motion of liquids and gases in which turbulences of all size scales occur
• Usually three-dimensional, apprarently random, non-stationary movements of fluid particles

### Air volume flow

A volumetric flow is taken to mean the volume of a medium that moves through a cross-section within a given period of time.

• Volume flow is usually stated either in l/s or in m³/h.
• The conversion calculation derives from 1000 l = 1 m³ and 3600 s = 1 h.
• The conversion factor is: 1 l/s = 3.6 m³/h or 1 m³/h = 0.27777777777778 l/s