3.1 Introduction
In the chemical and process industries, it is often required to pump fluids
over long distances from storage to various processing units and/or from one
plant site to another. There may be a substantial frictional pressure loss in
both the pipe line and in the individual units themselves. It is thus often
necessary to consider the problems of calculating the power requirements for
pumping through a given pipe network, the selection of optimum pipe diameter,
measurement and control of flow rate, etc. A knowledge of these factors
also facilitates the optimal design and layout of flow networks which may
represent a significant part of the total plant cost. Aside from circular pipes,
one also encounters conduits of other cross-sections and may be concerned
with axial flow in an annulus (as in a double pipe heat exchanger), rectangular,
triangular and elliptic conduits as employed in nuclear reactors and
for extrusion through dies. Furthermore, the velocity profile established in a
given flow situation strongly influences the heat and mass transfer processes.
For instance, the analysis and interpretation of data obtained in a standard
falling-film absorber used for the determination of diffusion coefficients relies
on the knowledge of flow kinematics. This chapter deals with engineering
relationships describing flow in a variety of geometries. The treatment here is,
however, restricted to the so-called purely viscous or time-independent type
of fluids, for which the viscosity model describing the flow curve is already
known. However, subsequently a generalised treatment for the laminar flow
of time-independent fluids in circular tubes is presented. Notwithstanding the
existence of time-dependent and visco-elastic fluid behaviour, experience has
shown that the shear rate dependence of the viscosity is the most significant
factor in most engineering applications which invariably operate under
steady state conditions. Visco-elastic behaviour does not significantly influence
laminar flow through circular tubes. Visco-elastic effects begin to manifest
themselves for flow in non-circular conduits and/or in pipe fittings. Even in
these circumstances, it is often possible to develop predictive expressions
purely in terms of steady-shear viscous properties.
Many of the formulae to be developed here will relate the frictional pressure
drop .??1p/ to the volumetric flow rate .Q/. The major application of such
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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