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In fluid dynamics, the entrance length is the distance a flow travels after entering a pipe before the flow becomes fully developed. [1] Entrance length refers to the length of the entry region , the area following the pipe entrance where effects originating from the interior wall of the pipe propagate into the flow as an expanding boundary layer .
L is the length Re is the Reynolds number and Pr is the Prandtl number. This number is useful in determining the thermally developing flow entrance length in ducts. A Graetz number of approximately 1000 or less is the point at which flow would be considered thermally fully developed. [2]
The equation does not hold close to the pipe entrance. [8]: 3 The equation fails in the limit of low viscosity, wide and/or short pipe. Low viscosity or a wide pipe may result in turbulent flow, making it necessary to use more complex models, such as the Darcy–Weisbach equation.
Knudsen equation – Description of gas flow in free molecular flow; Manning equation – Estimate of velocity in open channel flows; Mild-slope equation – Physics phenomenon and formula; Morison equation – Equation for force on an object in sea waves; Navier–Stokes equations – Equations describing the motion of viscous fluid substances
In engineering, the Moody chart or Moody diagram (also Stanton diagram) is a graph in non-dimensional form that relates the Darcy–Weisbach friction factor f D, Reynolds number Re, and surface roughness for fully developed flow in a circular pipe. It can be used to predict pressure drop or flow rate down such a pipe.
Hydrodynamic entrance length is that part of the tube in which the momentum boundary layer grows and the velocity distribution changes with length. The fixed velocity distribution in the fully developed region is called fully developed velocity profile. The steady-state continuity and conservation of momentum equations in two-dimensional are
Under a skimming flow regime, water flows in a coherent stream down the step. Water skims the top of each step as it flows down the chute. Recirculating vortices are developed between each step which allow the water to flow over the top of the vortices and skim over each step. [7]
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