Chemical Engineering Fluid Mechanics

Ron Darby, Raj P. Chhabra

• Publisher: CRC Press
• Year: 2016
• eBook ISBN: 9781498724449
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

This book provides readers with the most current, accurate, and practical fluid mechanics related applications that the practicing BS level engineer needs today in the chemical and related industries, in addition to a fundamental understanding of these applications based upon sound fundamental basic scientific principles. The emphasis remains on problem solving, and the new edition includes many more examples.

1	Basic Concepts

“Engineering is learning how to make a decision with insufficient information.”

—Anonymous

I. FUNDAMENTALS

A. INTRODUCTION AND SCOPE

The understanding of, and ability to predict, the flow behavior of fluids is fundamental to all aspects of the chemical engineering profession. Such behavior includes the relationship between the (driving) forces and the flow rates of various classes of fluids, and the characteristics of the equipment used to contain/handle/process these fluids. A wide variety of fluids with different properties may be encountered by the chemical engineer in the industrial applications that may be of concern in various chemical or petroleum process industries, biological or food and pharmaceutical industries, polymer and materials processing industries, etc. These properties range from common simple incompressible (Newtonian) liquids, that is, fluids such as water, oils, various petroleum fractions, etc., to complex nonlinear (non-Newtonian) fluids such as pastes, emulsions, foams, suspensions, high-molecular-weight polymeric fluids, biological fluids (e.g., blood), etc. as well as compressible (gaseous) fluids such as air, N₂, CO₂, etc. This book is concerned with the fundamental principles that govern the flow behavior of each of these types of fluids, as well as the resulting basic relationships needed to predict their behavior (relations between flow rates, pressures, forces on solid boundaries, etc.) and the corresponding analysis of a wide variety of equipment and practical situations commonly found in various industries. These principles are also applicable to such situations as the flow of blood in vessels, transport of sludge and silt in rivers and streams, pneumatic conveying of particles, the trajectory of a pitched baseball, etc.

B. BASIC LAWS

The fundamental principles that apply to the analysis of fluid flows are the three “conservation laws”:

1. Conservation of mass

2. Conservation of energy (the first law of thermodynamics)

3. Conservation of momentum (Newton’s second law of motion)

To which may be added

4. The second law of thermodynamics (i.e., will it work or not?)

5. Conservation of dimensions (e.g., the “fruit salad” law*)

6. Conservation of dollars (economics)

Although the second law of thermodynamics (#4) is not strictly a “conservation law,” it provides a practical limitation on what processes are possible or are most likely. It states that a process can occur spontaneously only if it goes from a state of higher energy to the one of lower energy (e.g., water will flow downhill by itself, but it must be “pushed” by expending energy in order to make it flow uphill).

These basic conservation laws provide relations between various fluid properties and operating conditions at different points within a system (see Section IV). In addition, appropriate rate or transport models are required that describe the rate at which these conserved quantities are transported from one part of the system to another. For example, if the mass of a given fluid element is m (e.g., kg or lb_m), the rate at which that mass is transported is the mass flow rate, ṁ (e.g., kg/s or lb_m/s). These conservation and rate laws are the starting point for the solution to every engineering problem.

The conservation of energy, for example, is often expressed in terms of the thermodynamic (equilibrium) properties of the system. This implies a system that is in a state of static equilibrium. However, most systems of interest to us are not at equilibrium but are dynamic (i.e., in motion) and it is the rate of transport of energy, mass, or momentum which is of interest. In order to transport energy at a finite rate, this equilibrium must be disturbed and additional “nonequilibrium” energy is required that depends upon the rate of transport. This “extra” energy is expended (e.g., dissipated or “lost”) by transformation from useful mechanical energy to low-grade thermal energy in order to transport mass, energy, or momentum at a finite rate. The farther from equilibrium the system is (i.e., the faster it goes), the greater is the resistance to motion (“friction”) and the greater is the energy that is “lost” or dissipated to a less useful low-grade thermal energy in order to overcome this resistance. In more ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• About Professor Darby
• Acknowledgments
• Unit Conversion Factors
• Chapter 1 Basic Concepts
• Chapter 2 Dimensional Analysis and Scale-Up
• Chapter 3 Fluid Properties in Perspective
• Chapter 4 Fluid Statics
• Chapter 5 Conservation Principles
• Chapter 6 Pipe Flow
• Chapter 7 Internal Flow Applications
• Chapter 8 Pumps and Compressors
• Chapter 9 Compressible Flows
• Chapter 10 Flow Measurement
• Chapter 11 Safety Relief and Control Valves
• Chapter 12 External Flows
• Chapter 13 Fluid-Solid Separations by Free Settling
• Chapter 14 Flow in Porous Media
• Chapter 15 Fluidization and Sedimentation
• Chapter 16 Two-Phase Flow
• Appendix A: Viscosities and Other Properties of Gases and Liquids
• Appendix B: Generalized Viscosity Plot
• Appendix C: Properties of Gases
• Appendix D: Pressure–Enthalpy Diagrams for Various Compounds
• Appendix E: Microscopic Conservation Equations in Rectangular, Cylindrical, and Spherical Coordinates
• Appendix F: Standard Steel Pipe Dimensions and Capacities
• Appendix G: Flow of Water/Air through Schedule 40 Pipe
• Appendix H: Typical Pump Head Capacity Range Charts
• Appendix I: Fanno Line Tables for Adiabatic Flow of Air in a Constant Area Duct
• Index