Page 58 - Fluid mechanics, heat transfer, and mass transfer

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PIPING, SEALS, AND VALVES

3.1 Friction and Piping 35 & Turbulent Flow:
3.2 Gaskets and Mechanical Seals 42
➢ Cooling of the liquid: The friction factor obtained
3.3 Valves 46
from the mean temperature and bulk properties is
divided by (bulk viscosity/wall viscosity) 0.11 .
➢ Heating of the liquid: The friction factor obtained
from the mean temperature and bulk properties is
divided by (bulk viscosity/wall viscosity) 0.17 .
➢ In turbulent flow, the bulk and the wall viscosities
3.1 FRICTION AND PIPING
are determined at the mean temperature over the
. What is friction factor? What is its significance? length of the line.
& Friction factor is a dimensionless quantity signifying . Give the equation for the estimation of pressure drop in
resistance offered by the wall of a pipe when a fluid pipeline flow of an incompressible fluid.
flows through it. & Fanning Equation:
. Give the equation for the estimation offriction factor for 2
laminar flow in a pipe. DP ¼ 4fLV =2D; ð3:3Þ
where f is the Fanning friction factor.
ðFanning friction factorÞ: ð3:1Þ
f ¼ 16=N Re & D’Arcy Equation:
0 ðD’ Archy friction factorÞ: 2
0
f ¼ 64=N Re ð3:2Þ DP ¼ f LV =2D; ð3:4Þ
. What are the effects of temperature changes on friction where D’Arcy friction factor is equal to four times the
factors? Fanning friction factor, f.
& Sieder–Tate gives corrections in equations for deter- . What is roughness factor/relative roughness?
mining friction factors inside heat exchanger tubes & Roughness factor or relative roughness is a dimen-
with varying temperatures: First, the average, bulk sionless number, defined as «/D, where « is the
meantemperatureintheprocessinglineisdetermined average length of surface projections, which consti-
toestimatethephysicalpropertiesandfrictionfactors. tute roughness of inner surface of the pipe in which a
& Laminar Flow: fluid is flowing and D is the inside diameter of the
➢ Cooling of the liquid: The friction factor obtained pipe.
from the mean temperature and bulk properties is . When «/D is more, are the friction losses more or less for
divided by (bulk viscosity/wall viscosity) 0.23 . the same Reynolds number? Why?
➢ Heating of the liquid: The friction factor obtained & More. Because increased roughness induces in-
from the mean temperature and bulk properties is creased turbulence, which results in higher frictional
divided by (bulk viscosity/wall viscosity) 0.38 . pressure losses for the flow.
➢ In laminar flow, the bulk and the wall viscosities . Give equation(s) and Moody chart for the estimation of
are determined at the mean temperature over the friction factors as function of N Re for turbulent flow in
length of the line. smooth and rough pipes.

Fluid Mechanics, Heat Transfer, and Mass Transfer: Chemical Engineering Practice, By K. S. N. Raju
Copyright Ó 2011 John Wiley & Sons, Inc.

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