# Welty Ingles 5 Ed Libro

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Fundamentals of Momentum,Heat, and Mass Transfer5th Edition

Fundamentals of Momentum,Heat, and Mass Transfer5th Edition

James R. Welty

Department of Mechanical Engineering

Charles E. Wicks

Department of Chemical Engineering

Robert E. Wilson

Department of Mechanical Engineering

Gregory L. Rorrer

Department of Chemical Engineering

Oregon State University

John Wiley & Sons, Inc.

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Preface to the 5th Edition

The rst edition of Fundamentals of Momentum, Heat, and Mass Transfer, published in1969, was written to become a part of what was then known as the engineering science

core of most engineering curricula. Indeed, requirements for ABET accreditation have

stipulated that a signicant part of all curricula must be devoted to fundamental subjects.

The emphasis on engineering science has continued over the intervening years, but the

degree of emphasis has diminished as new subjects and technologies have entered the

world of engineering education. Nonetheless, the subjects of momentum transfer (uid

mechanics), heat transfer, and mass transfer remain, at least in part, important components

of all engineering curricula. It is in this context that we now present the fth edition.

Advances in computing capability have been astonishing since 1969. At that time, the

pocket calculator was quite new and not generally in the hands of engineering students.

Subsequent editions of this book included increasingly sophisticated solution techniques as

technology advanced. Now,more than 30 years since the rst edition, computer competency

among students is a fait accompli and many homework assignments are completed using

computer software that takes care of most mathematical complexity, and a good deal of

physical insight. We do not judge the appropriateness of such approaches, but they surely

occur and will do so more frequently as software becomes more readily available, more

sophisticated, and easier to use.

In this edition, we still include some examples and problems that are posed in English

units, but a large portion of the quantitative work presented is now in SI units. This is

consistent withmost of the current generation of engineering textbooks. There are still some

subdisciplines in the thermal/uid sciences that use English units conventionally, so it

remains necessary for students to have some familiarity with pounds, mass, slugs, feet, psi,

and so forth. Perhaps a fth edition, if it materializes, will nally be entirely SI.

We, the original three authors (W3), welcome Dr. Greg Rorrer to our team. Greg is a

member of the faculty of the Chemical Engineering Department at Oregon State University

with expertise in biochemical engineering. He has had a signicant inuence on this

editions sections on mass transfer, both in the text and in the problem sets at the end of

Chapters 24 through 31. This edition is unquestionably strengthened by his contributions,

and we anticipate his continued presence on our writing team.

We are gratied that the use of this book has continued at a signicant level since the

rst edition appeared some 30 years ago. It is our continuing belief that the transport

phenomena remain essential parts of the foundation of engineering education and practice.

With the modications and modernization of this fourth edition, it is our hope that

Fundamentals of Momentum, Heat, and Mass Transfer will continue to be an essential

part of students educational experiences.

Corvallis, Oregon J.R. Welty

March 2000 C.E. Wicks

R.E. Wilson

G.L. Rorrer

v

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Contents

1. Introduction to Momentum Transfer 1

1.1 Fluids and the Continuum 1

1.2 Properties at a Point 2

1.3 Point-to-Point Variation of Properties in a Fluid 5

1.4 Units 8

1.5 Compressibility 9

1.6 Surface Tension 11

2. Fluid Statics 16

2.1 Pressure Variation in a Static Fluid 16

2.2 Uniform Rectilinear Acceleration 19

2.3 Forces on Submerged Surfaces 20

2.4 Buoyancy 23

2.5 Closure 25

3. Description of a Fluid in Motion 29

3.1 Fundamental Physical Laws 29

3.2 Fluid-Flow Fields: Lagrangian and Eulerian Representations 29

3.3 Steady and Unsteady Flows 30

3.4 Streamlines 31

3.5 Systems and Control Volumes 32

4. Conservation of Mass: Control-Volume Approach 34

4.1 Integral Relation 34

4.2 Specic Forms of the Integral Expression 35

4.3 Closure 39

5. Newtons Second Law of Motion: Control-Volume Approach 43

5.1 Integral Relation for Linear Momentum 43

5.2 Applications of the Integral Expression for Linear Momentum 46

5.3 Integral Relation for Moment of Momentum 52

5.4 Applications to Pumps and Turbines 53

5.5 Closure 57

6. Conservation of Energy: Control-Volume Approach 63

6.1 Integral Relation for the Conservation of Energy 63

6.2 Applications of the Integral Expression 69

vii

6.3 The Bernoulli Equation 72

6.4 Closure 76

7. Shear Stress in Laminar Flow 81

7.1 Newtons Viscosity Relation 81

7.2 Non-Newtonian Fluids 82

7.3 Viscosity 83

7.4 Shear Stress in Multidimensional Laminar Flows of a Newtonian Fluid 88

7.5 Closure 90

8. Analysis of a Differential Fluid Element in Laminar Flow 92

8.1 Fully Developed Laminar Flow in a Circular Conduit of Constant

Cross Section 92

8.2 Laminar Flow of a Newtonian Fluid Down an Inclined-Plane Surface 95

8.3 Closure 97

9. Differential Equations of Fluid Flow 99

9.1 The Differential Continuity Equation 99

9.2 Navier-Stokes Equations 101

9.3 Bernoullis Equation 110

9.4 Closure 111

10. Inviscid Fluid Flow 113

10.1 Fluid Rotation at a Point 113

10.2 The Stream Function 114

10.3 Inviscid, Irrotational Flow about an Innite Cylinder 116

10.4 Irrotational Flow, the Velocity Potential 117

10.5 Total Head in Irrotational Flow 119

10.6 Utilization of Potential Flow 119

10.7 Potential Flow AnalysisSimple Plane Flow Cases 120

10.8 Potential Flow AnalysisSuperposition 121

10.9 Closure 123

11. Dimensional Analysis and Similitude 125

11.1 Dimensions 125

11.2 Dimensional Analysis of Governing Differential Equations 126

11.3 The Buckingham Method 128

11.4 Geometric, Kinematic, and Dynamic Similarity 131

11.5 Model Theory 132

11.6 Closure 134

12. Viscous Flow 137

12.1 Reynoldss Experiment 137

12.2 Drag 138

viii Contents

12.3 The Boundary-Layer Concept 144

12.4 The Boundary-Layer Equations 145

12.5 Blasiuss Solution for the Laminar Boundary Layer on a Flat Plate 146

12.6 Flow with a Pressure Gradient 150

12.7 von Karman Momentum Integral Analysis 152

12.8 Description of Turbulence 155

12.9 Turbulent Shearing Stresses 157

12.10 The Mixing-Length Hypothesis 158

12.11 Velocity Distribution from the Mixing-Length Theory 160

12.12 The Universal Velocity Distribution 161

12.13 Further Empirical Relations for Turbulent Flow 162

12.14 The Turbulent Boundary Layer on a Flat Plate 163

12.15 Factors Affecting the Transition From Laminar to Turbulent Flow 165

12.16 Closure 165

13. Flow in Closed Conduits 168

13.1 Dimensional Analysis of Conduit Flow 168

13.2 Friction Factors for Fully Developed Laminar, Turbulent,

and Transition Flow in Circular Conduits 170

13.3 Friction Factor and Head-Loss Determination for Pipe Flow 173

13.4 Pipe-Flow Analysis 176

13.5 Friction Factors for Flow in the Entrance to a Circular Conduit 179

13.6 Closure 182

14. Fluid Machinery 185

14.1 Centrifugal Pumps 186

14.2 Scaling Laws for Pumps and Fans 194

14.3 Axial and Mixed Flow Pump Congurations 197

14.4 Turbines 197

14.5 Closure 197

15. Fundamentals of Heat Transfer 201

15.1 Conduction 201

15.2 Thermal Conductivity 202

15.3