###
Entry Length

Home ->
Lecture Notes
->
Fluid Mechanics -> Unit-II

There is an entrance region where a nearly inviscid upstream flow
converges and enters the tube. Viscous boundary layers grow downstream,
retarding the axial flow *v*(*x*, r) at the wall and thereby accelerating the
center-core flow to maintaintain the incompressible continuity requirement

Q = ò*v* dA = constant

At a finite distance from the entrance, the boundary layers merge and the
inviscid core disappears. The flow is then entirely viscous, and the axial
velocity adjusts slightly further until at *x* = L_{e} it no longer
changes with *x* and is said to be fully developed, *v* = *v*(r) only.
Downstream of *x* = L_{e} the veocity profile is constant, the wall
shear is constant, and the pressure drops linearly with x, for either
laminar or turbulent flow.

L_{e}/D = 0.06 Re_{D} for laminar

L_{e}/D = 4.4 Re_{D}^{1/6}
Where L_{e} is the entry length; and

Re_{D} is the Reynolds number based on Diameter.

Table of Contents

HOME

Last Modified on: 14-Sep-2014

Chemical Engineering Learning Resources - msubbu

e-mail: msubbu.in[AT]gmail.com

Web: http://www.msubbu.in