Mass Transfer Operations for the Practicing Engineerdownload.e-bookshelf.de/download/0000/5759/79/L-G-0000575979... · Humidiﬁcation and Drying 105 Other Mass Transfer Unit Operations

Mass Transfer Operationsfor the PracticingEngineerLouis TheodoreFrancesco Ricci

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Mass Transfer Operationsfor the PracticingEngineer

Mass Transfer Operationsfor the PracticingEngineerLouis TheodoreFrancesco Ricci

Copyright # 2010 by John Wiley & Sons, Inc. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Theodore, Louis.Mass transfer operations for the practicing engineer / Louis Theodore, Francesco Ricci.

p. cm.Includes Index.ISBN 978-0-470-57758-5 (hardback)

1. Engineering mathematics. 2. Mass transfer. I. Ricci, Francesco. II. Title.TA331.T476 2010530.407501512—dc22 2010013924

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

http://www.copyright.comhttp://www.wiley.comhttp://www.wiley.com/go/permission

To Ann Cadigan and Meg Norris:for putting up with me (LT)

and

To my mother Laura, my father Joseph,and my brother Joseph Jr:

for reasons which need not be spoken (FR)

Contents

Preface xv

Part One Introduction

1. History of Chemical Engineering and Mass Transfer Operations 3

References 5

2. Transport Phenomena vs Unit Operations Approach 7

References 10

3. Basic Calculations 11

Introduction 11Units and Dimensions 11Conversion of Units 15The Gravitational Constant gc 17Significant Figures and Scientific Notation 17References 18

4. Process Variables 19

Introduction 19Temperature 20Pressure 22Moles and Molecular Weight 23Mass, Volume, and Density 25Viscosity 25Reynolds Number 28pH 29Vapor Pressure 31Ideal Gas Law 31References 35

vii

5. Equilibrium vs Rate Considerations 37

Introduction 37Equilibrium 37Rate 38Chemical Reactions 39References 40

6. Phase Equilibrium Principles 41

Introduction 41Gibb’s Phase Rule 44Raoult’s Law 45Henry’s Law 53Raoult’s Law vs Henry’s Law 59Vapor–Liquid Equilibrium in Nonideal Solutions 61Vapor–Solid Equilibrium 64Liquid–Solid Equilibrium 68References 69

7. Rate Principles 71

Introduction 71The Operating Line 72Fick’s Law 73

Diffusion in Gases 75Diffusion in Liquids 79

Mass Transfer Coefficients 80

Individual Mass Transfer Coefficients 81Equimolar Counterdiffusion 83Diffusion of Component A Through Non-diffusing Component B 84

Overall Mass Transfer Coefficients 87

Equimolar Counterdiffusion and/or Diffusion in Dilute Solutions 88Gas Phase Resistance Controlling 89Liquid Phase Resistance Controlling 89Experimental Mass Transfer Coefficients 90

References 93

Part Two Applications: Component and Phase Separation Processes

8. Introduction to Mass Transfer Operations 97

Introduction 97

viii Contents

Classification of Mass Transfer Operations 97

Contact of Immiscible Phases 98Miscible Phases Separated by a Membrane 101Direct Contact of Miscible Phases 102

Mass Transfer Equipment 102

Distillation 103Absorption 104Adsorption 104Extraction 104Humidification and Drying 105Other Mass Transfer Unit Operations 105The Selection Decision 106

Characteristics of Mass Transfer Operations 107

Unsteady-State vs Steady-State Operation 108Flow Pattern 109Stagewise vs Continuous Operation 116

References 117

9. Distillation 119

Introduction 119Flash Distillation 120Batch Distillation 127Continuous Distillation with Reflux 133

Equipment and Operation 133Equilibrium Considerations 140Binary Distillation Design: McCabe–Thiele Graphical Method 142Multicomponent Distillation: Fenske–Underwood–Gilliland (FUG)

Method 161Packed Column Distillation 184

References 185

10. Absorption and Stripping 187

Introduction 187Description of Equipment 189

Packed Columns 189Plate Columns 196

Design and Performance Equations—Packed Columns 200

Liquid Rate 200Column Diameter 207Column Height 210Pressure Drop 224

Contents ix

Design and Performance Equations—Plate Columns 227Stripping 235Packed vs Plate Tower Comparison 241Summary of Key Equations 242References 243

11. Adsorption 245

Introduction 245Adsorption Classification 247

Activated Carbon 248Activated Alumina 248Silica Gel 249Molecular Sieves 249

Adsorption Equilibria 250

Freundlich Equation 253Langmuir Isotherms 253

Description of Equipment 257Design and Performance Equations 264Regeneration 283References 291

12. Liquid–Liquid and Solid–Liquid Extraction 293

Introduction 293Liquid–Liquid Extraction 294

The Extraction Process 294Equipment 295Solvent Selection 298Equilibrium 300Graphical Procedures 301Analytical Procedures 304

Solid–Liquid Extraction (Leaching) 312

Process Variables 313Equipment and Operation 315Design and Predictive Equations 317

References 325

13. Humidification and Drying 327

Introduction 327Psychrometry and the Psychrometric Chart 327Humidification 339

x Contents

Equipment 341Describing Equations 343

Drying 347

Rotary Dryers 352Spray Dryers 361

References 369

14. Crystallization 371

Introduction 371Phase Diagrams 373The Crystallization Process 379Crystal Physical Characteristics 382Equipment 391Describing Equations 393Design Considerations 397References 404

15. Membrane Separation Processes 407

Introduction 407Reverse Osmosis 408

Describing Equations 414

Ultrafiltration 420


Microfiltration 427


Gas Permeation 432


References 437

16. Phase Separation Equipment 439

Introduction 439Fluid–Particle Dynamics 442Gas–Solid (G–S) Equipment 446

Gravity Settlers 447Cyclones 449Electrostatic Precipitators 454Venturi Scrubbers 457Baghouses 461

Contents xi

Gas–Liquid (G–L) Equipment 465Liquid–Solid (L–S) Equipment 467

Sedimentation 467Centrifugation 471Flotation 472

Liquid–Liquid (L–L) Equipment 475Solid–Solid (S–S) Equipment 477

High-Gradient Magnetic Separation 477Solidification 477

References 479

Part Three Other Topics

17. Other and Novel Separation Processes 483

Freeze Crystallization 484Ion Exchange 484Liquid Ion Exchange 484Resin Adsorption 485Evaporation 485Foam Fractionation 486Dissociation Extraction 486Electrophoresis 486Vibrating Screens 487References 488

18. Economics and Finance 489

Introduction 489The Need for Economic Analyses 489Definitions 491

Simple Interest 491Compound Interest 491Present Worth 492Evaluation of Sums of Money 492Depreciation 493Fabricated Equipment Cost Index 493Capital Recovery Factor 493Present Net Worth 494Perpetual Life 494Break-Even Point 495Approximate Rate of Return 495

xii Contents

Exact Rate of Return 495Bonds 496Incremental Cost 496

Principles of Accounting 496Applications 499References 511

19. Numerical Methods 513

Introduction 513Applications 514References 531

20. Open-Ended Problems 533

Introduction 533Developing Students’ Power of Critical Thinking 534Creativity 534Brainstorming 536Inquiring Minds 536Failure, Uncertainty, Success: Are TheyRelated? 537

Angels on a Pin 538Applications 539References 547

21. Ethics 549

Introduction 549Teaching Ethics 550Case Study Approach 551Integrity 553Moral Issues 554Guardianship 556Engineering and Environmental Ethics 557Future Trends 559Applications 561References 563

22. Environmental Management and Safety Issues 565

Introduction 565Environmental Issues of Concern 566Health Risk Assessment 568

Risk Evaluation Process for Health 570

Contents xiii

Hazard Risk Assessment 571

Risk Evaluation Process for Accidents 572

Applications 574References 591

Appendix

Appendix A. Units 595

A.1 The Metric System 595A.2 The SI System 597A.3 Seven Base Units 597A.4 Two Supplementary Units 598A.5 SI Multiples and Prefixes 599A.6 Conversion Constants (SI) 599A.7 Selected Common Abbreviations 603

Appendix B. Miscellaneous Tables 605

Appendix C. Steam Tables 615

Index 623

xiv Contents

Preface

Mass transfer is one of the basic tenets of chemical engineering, and contains manypractical concepts that are utilized in countless industrial applications. Therefore,the authors considered writing a practical text. The text would hopefully serve as atraining tool for those individuals in academia and industry involved with masstransfer operations. Although the literature is inundated with texts emphasizingtheory and theoretical derivations, the goal of this text is to present the subject froma strictly pragmatic point-of-view.

The book is divided into three parts: Introduction, Applications, and OtherTopics. The first part provides a series of chapters concerned with principles thatare required when solvingmost engineering problems, including those in mass transferoperations. The second part deals exclusively with specific mass transfer operationse.g., distillation, absorption and stripping, adsorption, and so on. The last partprovides an overview of ABET (Accreditation Board for Engineering andTechnology) related topics as they apply to mass transfer operations plus novelmass transfer processes. An Appendix is also included. An outline of the topicscovered can be found in the Table of Contents.

The authors cannot claim sole authorship to all of the essay material andillustrative examples in this text. The present book has evolved from a host of sources,including: notes, homework problems and exam problems prepared by several facultyfor a required one-semester, three-credit, “Principles III: Mass Transfer” undergradu-ate course offered at Manhattan College; L. Theodore and J. Barden, “Mass Transfer”,ATheodore Tutorial, East Williston, NY, 1994; J. Reynolds, J. Jeris, and L. Theodore,“Handbook of Chemical and Environmental Engineering Calculations,” John Wiley& Sons, Hoboken, NJ, 2004, and J. Santoleri, J. Reynolds, and L. Theodore,“Introduction to Hazardous Waste Management,” 2nd edition, John Wiley & Sons,Hoboken, NJ, 2000. Although the bulk of the problems are original and/or takenfrom sources that the authors have been directly involved with, every effort hasbeen made to acknowledge material drawn from other sources.

It is hoped that we have placed in the hands of academic, industrial, andgovernment personnel, a book that covers the principles and applications of masstransfer in a thorough and clear manner. Upon completion of the text, the readershould have acquired not only a working knowledge of the principles of mass transferoperations, but also experience in their application; and, the reader should find him-self/herself approaching advanced texts, engineering literature and industrial appli-cations (even unique ones) with more confidence. We strongly believe that, whileunderstanding the basic concepts is of paramount importance, this knowledge may

xv

be rendered virtually useless to an engineer if he/she cannot apply these concepts toreal-world situations. This is the essence of engineering.

Last, but not least, we believe that this modest work will help the majority of indi-viduals working and/or studying in the field of engineering to obtain a more completeunderstanding of mass transfer operations. If you have come this far and read throughmost of the Preface, you have more than just a passing interest in this subject. Westrongly suggest that you try this text; we think you will like it.

Our sincere thanks are extended to Dr. Paul Marnell at Manhattan College for hisinvaluable help in contributing to Chapter 9 on Distillation and Chapter 14 onCrystallization. Thanks are also due to Anne Mohan for her assistance in preparingthe first draft of Chapter 13 (Humidification and Drying) and to Brian Berminghamand Min Feng Zheng for their assistance during the preparation of Chapter 12(Liquid–Liquid and Solid–Liquid Extraction). Finally, Shannon O’Brien, KathrynScherpf and Kimberly Valentine did an exceptional job in reviewing the manuscriptand page proofs.

FRANCESCO RICCIApril 2010 LOUIS THEODORE

NOTE: An additional resource is available for this text. An accompanying websitecontains over 200 additional problems and 15 hours of exams; solutions for theproblems and exams are available at www.wiley.com for those who adopt the bookfor training and/or academic purposes.

xvi Preface

Part One

IntroductionThe purpose of this Part can be found in its title. The book itself offers the readerthe fundamentals of mass transfer operations with appropriate practical applications,and serves as an introduction to the specialized and more sophisticated texts in thisarea. The reader should realize that the contents are geared towards practitioners inthis field, as well as students of science and engineering, not chemical engineers perse. Simply put, topics of interest to all practicing engineers have been included.Finally, it should alsobenoted that themicroscopic approachofmass transferoperationsis not treated in any requiredundergraduateManhattanCollegeoffering.TheManhattanapproach is to place more emphasis on real-world and design applications. However,microscopic approachmaterial is available in the literature, as noted in the ensuing chap-ters. The decision on whether to include the material presented ultimately depends onthe reader and/or the approach and mentality of both the instructor and the institution.

A general discussion of the philosophy and the contents of this introductorysection follows.

Since the chapters in this Part provide an introduction and overview of mass trans-fer operations, there is some duplication due to the nature of the overlapping nature ofoverview/introductory material, particularly those dealing with principles. Part Onechapter contents include:

1 History of Chemical Engineering and Mass Transfer Operations

2 Transport Phenomena vs Unit Operations Approach

3 Basic Calculations

4 Process Variables

5 Equilibrium vs Rate Considerations

6 Phase Equilibrium Principles

7 Rate Principles

Topics covered in the first two introductory chapters include a history of chemicalengineering and mass transfer operations, and a discussion of transport phenomenavs unit operations. The remaining chapters are concerned with introductoryengineering principles. The next Part is concerned with describing and designingthe various mass transfer unit operations and equipment.

Mass Transfer Operations for the Practicing Engineer. By Louis Theodore and Francesco RicciCopyright # 2010 John Wiley & Sons, Inc.

1

Chapter 1

History of ChemicalEngineering and MassTransfer Operations

A discussion on the field of chemical engineering is warranted before proceeding tosome specific details regarding mass transfer operations (MTO) and the contents ofthis first chapter. A reasonable question to ask is: What is Chemical Engineering?An outdated, but once official definition provided by the American Institute ofChemical Engineers is:

Chemical Engineering is that branch of engineering concerned with the developmentand application of manufacturing processes in which chemical or certain physicalchanges are involved. These processes may usually be resolved into a coordinated seriesof unit physical “operations” (hence part of the name of the chapter and book) and chemicalprocesses. The work of the chemical engineer is concerned primarily with the design,construction, and operation of equipment and plants in which these unit operations andprocesses are applied. Chemistry, physics, and mathematics are the underlying sciences ofchemical engineering, and economics is its guide in practice.

The above definition was appropriate up until a few decades ago when the professionbranched out from the chemical industry. Today, that definition has changed.Although it is still based on chemical fundamentals and physical principles, these prin-ciples have been de-emphasized in order to allow for the expansion of the profession toother areas (biotechnology, semiconductors, fuel cells, environment, etc.). These areasinclude environmental management, health and safety, computer applications, andeconomics and finance. This has led to many new definitions of chemical engineering,several of which are either too specific or too vague. A definition proposed here issimply that “Chemical Engineers solve problems”. Mass transfer is the one subjectarea that somewhat uniquely falls in the domain of the chemical engineer. It isoften presented after fluid flow(1) and heat transfer,(2) since fluids are involved aswell as heat transfer and heat effects can become important in any of the mass transferunit operations.


3

A classical approach to chemical engineering education, which is still usedtoday, has been to develop problem solving skills through the study of severaltopics. One of the topics that has withstood the test of time is mass transfer operations;the area that this book is concerned with. In many mass transfer operations, onecomponent of a fluid phase is transferred to another phase because the componentis more soluble in the latter phase. The resulting distribution of components betweenphases depends upon the equilibrium of the system. Mass transfer operations may alsobe used to separate products (and reactants) and may be used to remove byproductsor impurities to obtain highly pure products. Finally, it can be used to purify rawmaterials.

Although the chemical engineering profession is usually thought to haveoriginated shortly before 1900, many of the processes associated with this disciplinewere developed in antiquity. For example, filtration operations were carried out5000 years ago by the Egyptians. MTOs such as crystallization, precipitation, anddistillation soon followed. During this period, other MTOs evolved from a mixtureof craft, mysticism, incorrect theories, and empirical guesses.

In a very real sense, the chemical industry dates back to prehistoric times whenpeople first attempted to control and modify their environment. The chemical industrydeveloped as did any other trade or craft. With little knowledge of chemical scienceand no means of chemical analysis, the earliest chemical “engineers” had to rely onprevious art and superstition. As one would imagine, progress was slow. This changedwith time. The chemical industry in the world today is a sprawling complex ofraw-material sources, manufacturing plants, and distribution facilities which supplysociety with thousands of chemical products, most of which were unknown over acentury ago. In the latter half of the nineteenth century, an increased demand arosefor engineers trained in the fundamentals of chemical processes. This demand wasultimately met by chemical engineers.

The first attempt to organize the principles of chemical processing and to clarifythe professional area of chemical engineering was made in England by George E.Davis. In 1880, he organized a Society of Chemical Engineers and gave a series oflectures in 1887 which were later expanded and published in 1901 as A Handbookof Chemical Engineering. In 1888, the first course in chemical engineering in theUnited States was organized at the Massachusetts Institute of Technology byLewis M. Norton, a professor of industrial chemistry. The course applied aspects ofchemistry and mechanical engineering to chemical processes.(3)

Chemical engineering began to gain professional acceptance in the early years ofthe twentieth century. The American Chemical Society had been founded in 1876 and,in 1908, it organized a Division of Industrial Chemists and Chemical Engineers whileauthorizing the publication of the Journal of Industrial and Engineering Chemistry.Also in 1908, a group of prominent chemical engineers met in Philadelphia andfounded the American Institute of Chemical Engineers.(3)

The mold for what is now called chemical engineering was fashioned at the 1922meeting of the American Institute of Chemical Engineers when A. D. Little’s commit-tee presented its report on chemical engineering education. The 1922 meeting markedthe official endorsement of the unit operations concept and saw the approval of a

4 Chapter 1 History of Chemical Engineering and Mass Transfer Operations

“declaration of independence” for the profession.(3) A key component of this reportincluded the following:

Any chemical process, on whatever scale conducted, may be resolved into acoordinated series of what may be termed “unit operations,” as pulverizing, mixing,heating, roasting, absorbing, precipitation, crystallizing, filtering, dissolving, and so on.The number of these basic unit operations is not very large and relatively few of themare involved in any particular process. . .An ability to cope broadly and adequately with thedemands of this (the chemical engineer’s) profession can be attained onlythrough the analysis of processes into the unit actions as they are carried out on thecommercial scale under the conditions imposed by practice.

It also went on to state that:

Chemical Engineering, as distinguished from the aggregate number of subjectscomprised in courses of that name, is not a composite of chemistry and mechanical andcivil engineering, but is itself a branch of engineering. . .

A time line diagram of the history of chemical engineering between theprofession’s founding to the present day is shown in Figure 1.1.(3) As can be seenfrom the time line, the profession has reached a crossroads regarding the future edu-cation/curriculum for chemical engineers. This is highlighted by the differences ofTransport Phenomena and Unit Operations, a topic that is treated in the next chapter.

REFERENCES

1. P. ABULENCIA and L. THEODORE, “Fluid Flow for the Practicing Engineer,” JohnWiley & Sons, Hoboken,NJ, 2009.

2. L. THEODORE, “Heat Transfer for the Practicing Engineer,” John Wiley & Sons, Hoboken, NJ, 2011(in preparation).

3. N. SERINO, “2005 Chemical Engineering 125th Year Anniversary Calendar,” term project, submitted toL. Theodore, 2004.

4. R. BIRD, W. STEWART, and E. LIGHTFOOT, “Transport Phenomena,” 2nd edition, John Wiley & Sons,Hoboken, NJ, 2002.

NOTE: Additional problems are available for all readers at www.wiley.com. Followlinks for this title. These problems may be used for additional review, homework,and/or exam purposes.

History of Chemical Engineering and Mass Transfer Operations 5

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6

Chapter 2

Transport Phenomena vs UnitOperations Approach

The history of Unit Operations is interesting. As indicated in the previous chapter,chemical engineering courses were originally based on the study of unit processesand/or industrial technologies. However, it soon became apparent that the changesproduced in equipment from different industries were similar in nature, i.e., therewas a commonality in the mass transfer operations in the petroleum industry as withthe utility industry. These similar operations became known as Unit Operations.This approach to chemical engineering was promulgated in the Little report discussedearlier, and has, with varying degrees and emphasis, dominated the profession tothis day.

The Unit Operations approach was adopted by the profession soon after itsinception. During the 130 years (since 1880) that the profession has been in existenceas a branch of engineering, society’s needs have changed tremendously and so haschemical engineering.

The teaching of Unit Operations at the undergraduate level has remained rela-tively unchanged since the publication of several early- to mid-1900 texts. However,by the middle of the 20th century, there was a slow movement from the unit operationconcept to a more theoretical treatment called transport phenomena or, more simply,engineering science. The focal point of this science is the rigorous mathematicaldescription of all physical rate processes in terms of mass, heat, or momentum crossingphase boundaries. This approach took hold of the education/curriculum of theprofession with the publication of the first edition of the Bird et al. book.(1) Some,including both authors of this text, feel that this concept set the profession back severaldecades since graduating chemical engineers, in terms of training, were more appliedphysicists than traditional chemical engineers. There has fortunately been a return tothe traditional approach to chemical engineering, primarily as a result of the efforts ofABET (Accreditation Board for Engineering and Technology). Detractors to thispragmatic approach argue that this type of theoretical education experience providesanswers to what and how, but not necessarily why, i.e., it provides a greater under-standing of both fundamental physical and chemical processes. However, in terms


7

of reality, nearly all chemical engineers are now presently involved with the whyquestions. Therefore, material normally covered here has been replaced, in part, witha new emphasis on solving design and open-ended problems; this approach isemphasized in this text.

The following paragraphs attempt to qualitatively describe the differencesbetween the above two approaches. Both deal with the transfer of certain quantities(momentum, energy, and mass) from one point in a system to another. There arethree basic transport mechanisms which can potentially be involved in a process.They are:

1 Radiation

2 Convection

3 Molecular Diffusion

The first mechanism, radiative transfer, arises as a result of wave motion and is notconsidered, since it may be justifiably neglected in most engineering applications.The second mechanism, convective transfer, occurs simply because of bulk motion.The final mechanism, molecular diffusion, can be defined as the transport mechanismarising as a result of gradients. For example, momentum is transferred in the presenceof a velocity gradient; energy in the form of heat is transferred because of a temperaturegradient; and, mass is transferred in the presence of a concentration gradient. Thesemolecular diffusion effects are described by phenomenological laws.(1)

Momentum, energy, and mass are all conserved. As such, each quantity obeys theconservation law within a system:

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The conservation law may be applied at the macroscopic, microscopic, ormolecular level.

One can best illustrate the differences in these methods with an example. Considera system in which a fluid is flowing through a cylindrical tube (see Fig. 2.1) and definethe system as the fluid contained within the tube between points 1 and 2 at any time. Ifone is interested in determining changes occurring at the inlet and outlet of a system,the conservation law is applied on a “macroscopic” level to the entire system. Theresultant equation (usually algebraic) describes the overall changes occurring to thesystem (or equipment). This approach is usually applied in the Unit Operation

8 Chapter 2 Transport Phenomena vs Unit Operations Approach

(or its equivalent) courses, an approach which is highlighted in this text and itstwo companion texts.(2,3)

In the microscopic/transport phenomena approach, detailed information con-cerning the behavior within a system is required; this is occasionally requested ofand by the engineer. The conservation law is then applied to a differential elementwithin the system that is large compared to an individual molecule, but small com-pared to the entire system. The resulting differential equation is then expanded viaan integration in order to describe the behavior of the entire system.

The molecular approach involves the application of the conservation laws toindividual molecules. This leads to a study of statistical and quantum mechanics—both of which are beyond the scope of this text. In any case, the description at themolecular level is of little value to the practicing engineer. However, the statisticalaveraging of molecular quantities in either a differential or finite element within asystem can lead to a more meaningful description of the behavior of a system.

Both the microscopic and molecular approaches shed light on the physicalreasons for the observed macroscopic phenomena. Ultimately, however, for the practi-cing engineer, these approaches may be valid but are akin to attempting to kill a flywith a machine gun. Developing and solving these equations (in spite of the adventof computer software packages) is typically not worth the trouble.

Traditionally, the applied mathematician has developed differential equationsdescribing the detailed behavior of systems by applying the appropriate conser-vation law to a differential element or shell within the system. Equations were derivedwith each new application. The engineer later removed the need for these tediousand error-prone derivations by developing a general set of equations that couldbe used to describe systems. These have come to be referred to by many as thetransport equations. In recent years, the trend toward expressing these equations invector form has gained momentum (no pun intended). However, the shell-balanceapproach has been retained in most texts where the equations are presented incomponential form, i.e., in three particular coordinate systems—rectangular, cylindri-cal, and spherical. The componential terms can be “lumped” together to produce amore concise equation in vector form. The vector equation can be, in turn, re-expandedinto other coordinate systems. This information is available in the literature.(1,4)

Fluid in

1 2

1 2

Fluid out

Figure 2.1 Flow system.

Transport Phenomena vs Unit Operations Approach 9

ILLUSTRATIVE EXAMPLE 2.1

Explain why the practicing engineer/scientist invariably employs the macroscopic approach inthe solution of real world problems.

SOLUTION: The macroscopic approach involves examining the relationship betweenchanges occurring at the inlet and the outlet of a system. This approach attempts to identifyand solve problems found in the real world, and is more straightforward than and preferableto the more involved microscopic approach. The microscopic approach, which requires anunderstanding of all internal variations taking placewithin the system that can lead up to an over-all system result, simply may not be necessary. B

REFERENCES

1. R. BIRD, W. STEWART, and E. LIGHTFOOT, “Transport Phenomena,” John Wiley & Sons, Hoboken,NJ, 1960.

2. L. THEODORE, “Heat Transfer for the Practicing Engineer,” John Wiley & Sons, Hoboken, NJ, 2011(in preparation).

3. P. ABULENCIA and L. THEODORE, “Fluid Flow for the Practicing Engineer,” JohnWiley & Sons, Hoboken,NJ, 2009.

4. L. THEODORE, “Introduction to Transport Phenomena,” International Textbook Co., Scranton, PA, 1970.

NOTE: Additional problems are available for all readers at www.wiley.com. Followlinks for this title. These problems may be used for additional review, homework,and/or exam purposes.

10 Chapter 2 Transport Phenomena vs Unit Operations Approach

Chapter 3

Basic Calculations

INTRODUCTION

This chapter provides a review of basic calculations and the fundamentals ofmeasurement. Four topics receive treatment:

1 Units and Dimensions

2 Conversion of Units

3 The Gravitational Constant, gc4 Significant Figures and Scientific Notation

The reader is directed to the literature in the Reference section of this chapter(1–3) foradditional information on these four topics.

UNITS AND DIMENSIONS

The units used in this text are consistent with those adopted by the engineeringprofession in the United States. For engineering work, SI (Système International)and English units are most often employed. In the United States, the English engineer-ing units are generally used, although efforts are still underway to obtain universaladoption of SI units for all engineering and science applications. The SI units havethe advantage of being based on the decimal system, which allows for more con-venient conversion of units within the system. There are other systems of units;some of the more common of these are shown in Table 3.1. Although English engin-eering units will primarily be used, Tables 3.2 and 3.3 present units for both theEnglish and SI systems, respectively. Some of the more common prefixes for SIunits are given in Table 3.4 (see also Appendix A.5) and the decimal equivalentsare provided in Table 3.5. Conversion factors between SI and English units andadditional details on the SI system are provided in Appendices A and B.


11

Tab

le3.1

Com

mon

Systemsof

Units

System

Length

Tim

eMass

Force

Energy

Tem

perature

SI

meter

second

kilogram

New

ton

Joule

Kelvin,

degree

Celsius

egs

centim

eter

second

gram

dyne

erg,Joule,or

calorie

Kelvin,

degree

Celsius

fps

foot

second

pound

poundal

foot

poundal

degree

Rankine,d

egree

Fahrenheit

American

Engineering

foot

second

pound

pound(force)

Britishthermalunit,

horsepow

er. hour

degree

Rankine,d

egree

Fahrenheit

BritishEngineering

foot

second

slug

pound(force)

Britishthermalunit,

foot

pound(force)

degree

Rankine,d

egree

Fahrenheit

12

Documents

Mass Transfer Operations for the Practicing Engineerdownload.e-bookshelf.de/download/0000/5759/79/L-G-0000575979... · Humidiﬁcation and Drying 105 Other Mass Transfer Unit Operations