Chemical Engineering Fluid Mechanics - Ron Darby.pdf - chemia - draco888888

ISBN: 0-8247-0444-4

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Preface

The objectives of this book are twofold: (1) for the student, to show how the

fundamental principles underlying the behavior of ﬂuids (with emphasis on

one-dimensional macroscopic balances) can be applied in an organized and

systematic manner to the solution of practical engineering problems, and (2)

for the practicing engineer, to provide a ready reference of current informa-

tion and basic methods for the analysis of a variety of problems encountered

in practical engineering situations.

The scope of coverage includes internal ﬂows of Newtonian and non-

Newtonian incompressible ﬂuids, adiabatic and isothermal compressible

ﬂows (up to sonic or choking conditions), two-phase (gas–liquid, solid–

liquid, and gas–solid) ﬂows, external ﬂows (e.g., drag), and ﬂow in porous

media. Applications include dimensional analysis and scale-up, piping sys-

tems with ﬁttings for Newtonian and non-Newtonian ﬂuids (for unknown

driving force, unknown ﬂow rate, unknown diameter, or most economical

diameter), compressible pipe ﬂows up to choked ﬂow, ﬂow measurement

and control, pumps, compressors, ﬂuid-particle separation methods (e.g.,

iii

Preface

centrifugal, sedimentation, ﬁltration), packed columns, ﬂuidized beds, sedi-

mentation, solids transport in slurry and pneumatic ﬂow, and frozen and

ﬂashing two-phase gas–liquid ﬂows. The treatment is from the viewpoint of

the process engineer, who is concerned with equipment operation, perfor-

mance, sizing, and selection, as opposed to the details of mechanical design

or the details of ﬂow patterns in such situations.

For the student, this is a basic text for a ﬁrst-level course in process

engineering ﬂuid mechanics, which emphasizes the systematic application of

fundamental principles (e.g., macroscopic mass, energy, and momentum

balances and economics) to the analysis of a variety of ﬂuid problems of

a practical nature. Methods of analysis of many of these operations have

been taken from the recent technical literature, and have not previously been

available in textbooks. This book includes numerous problems that illus-

trate these applications at the end of each chapter.

For the practicing engineer, this book serves as a useful reference for

the working equations that govern many applications of practical interest,

as well as a source for basic principles needed to analyze other ﬂuid systems

not covered explicitly in the book. The objective here is not to provide a

mindless set of recipes for rote application, however, but to demonstrate an

organized approach to problem analysis beginning with basic principles and

ending with results of very practical applicability.

Chemical Engineering Fluid Mechanics is based on notes that I have

complied and continually revised while teaching the junior-level ﬂuid

mechanics course for chemical engineering students at Texas A&M

University over the last 30 years. It has been my experience that, when

being introduced to a new subject, students learn best by starting with

simple special cases that they can easily relate to physically, and then pro-

gressing to more generalized formulations and more complex problems.

That is the philosophy adopted in this book. It will certainly be criticized

by some, since it is contrary to the usual procedure followed by most text-

books, in which the basic principles are presented ﬁrst in the most general

and mathematical form (e.g., the divergence theorem, Reynolds transport

theorem, Navier Stokes equations, etc.), and the special cases are then

derived from these. Esoterically, it is very appealing to progress from the

general to the speciﬁc, rather than vice versa. However, having taught from

both perspectives, it is my observation that most beginning students do not

gain an appreciation or understanding from the very general, mathemati-

cally complex, theoretical vector expressions until they have gained a certain

physical feel for how ﬂuids behave, and the laws governing their behavior, in

special situations to which they can easily relate. They also understand and

appreciate the principles much better if they see how they can be applied to

the analysis of practical and useful situations, with results that actually work

Preface

in practice. That is why the multi-dimensional vector generalizations of

the basic conservations laws have been eschewed in favor of the simpler

component and one-dimensional form of these laws.

It is also important to maintain a balanced perspective between funda-

mental, or theoretical, and empirical information, for the practicing

engineer must use both to be effective. It has been said that all the tools

of mathematics and physics in the world are not sufﬁcient to calculate how

much water will ﬂow in a given time from a kitchen tap when it is opened.

However, by proper formulation and utilization of certain experimental

observations, this is a routine problem for the engineer. The engineer

must be able to solve certain problems by direct application of theoretical

principles only (e.g., laminar ﬂow in uniform conduits), others by utilizing

hypothetical models that account for a limited understanding of the basic

ﬂow phenomena by incorporation of empirical parameters (e.g., :turbulent

ﬂow in conduits and ﬁttings), and still other problems in which important

information is purely empirical (e.g., pump efﬁciencies, two-phase ﬂow in

packed columns). In many of these problems (of all types), application of

dimensional analysis (or the principle of ‘‘conservation of dimensions’’) for

generalizing the results of speciﬁc analysis, guiding experimental design, and

scaling up both theoretical and experimental results can be a very powerful

tool.

This second edition of the book includes a new chapter on two-phase

ﬂow, which deals with solid–liquid, solid–gas, and frozen and ﬂashing

liquid–gas systems, as well as revised, updated, and extended material

throughout each chapter. For example, the method for selecting the proper

control valve trim to use with a given piping conﬁguration is presented and

illustrated by example in Chapter 10. The section on cyclone separators has

been completely revised and updated, and new material has been incorpo-

rated in a revision of the material on particles in non-Newtonian ﬂuids.

Changes have made throughout the book in an attempt to improve the

clarity and utility of the presentation wherever possible. For example, the

equations for compressible ﬂow in pipes have been reformulated in terms of

variables that are easier to evaluate and represent in dimensionless form.

It is the aim of this book to provide a useful introduction to the

simpliﬁed form of basic governing equations and an illustration of a con-

sistent method of applying these to the analysis of a variety of practical ﬂow

problems. Hopefully, the reader will use this as a starting point to delve

more deeply into the limitless expanse of the world of ﬂuid mechanics.

Ron Darby

Chemical Engineering Fluid Mechanics - Ron Darby.pdf

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