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Design of Fluid Thermal Systems

Janna, William S.

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This book is designed to serve senior-level engineering students taking a capstone design course in fluid and thermal systems design. It is built from the ground up with the needs and interests of practicing engineers in mind; the emphasis is on practical applications. The book begins with a discussion of design methodology, including the process of bidding to obtain a project, and project management techniques. The text continues with an introductory overview of fluid thermal systems (a pump and pumping system, a household air conditioner, a baseboard heater, a water slide, and a vacuum cleaner are among the examples given), and a review of the properties of fluids and the equations of fluid mechanics. The text then offers an in-depth discussion of piping systems, including the economics of pipe size selection. Janna examines pumps (including net positive suction head considerations) and piping systems. He provides the reader with the ability to design an entire system for moving fluids that is efficient and cost-effective. Next, the book provides a review of basic heat transfer principles, and the analysis of heat exchangers, including double pipe, shell and tube, plate and frame cross flow heat exchangers. Design considerations for these exchangers are also discussed. The text concludes with a chapter of term projects that may be undertaken by teams of students.

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Design of Fluid Thermal Systems Fourth Edition William S. Janna The University of Memphis Australia • Brazil • Japan • Korea • Mexico • Singapore • Spain • United Kingdom • United States Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. This is an electronic version of the print textbook. Due to electronic rights restrictions, some third party content may be suppressed. Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. The publisher reserves the right to remove content from this title at any time if subsequent rights restrictions require it. For valuable information on pricing, previous editions, changes to current editions, and alternate formats, please visit www.cengage.com/highered to search by ISBN#, author, title, or keyword for materials in your areas of interest. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Design of Fluid Thermal Systems, Fourth Edition William S. Janna Publisher, Global Engineering: Timothy Anderson Developmental Editor: Eavan Cully Editorial Assistant: Ashley Kaupert Art and Cover Direction, Production Management: PreMediaGlobal Compositor: William S. Janna Senior Intellectual Property Director: ; Julie Geagan-Chevez Intellectual Property Project Manager: Amber Hosea Text & Image Permissions Researcher: Kristiina Paul Manufacturing Planner: Doug Wilke Cover Image(s): Top image: ©nostal6ie/ www.Shutterstock.com Background image: ©areacre/Masterfile © 2015, 2010 Cengage Learning WCN: 02-200-203 ALL RIGHTS RESERVED. No part of this work covered by the copyright herein may be reproduced, transmitted, stored, or used in any form or by any means graphic, electronic, or mechanical, including but not limited to photocopying, recording, scanning, digitizing, taping, web distribution, information networks, or information storage and retrieval systems, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without the prior written permission of the publisher. For product information and technology assistance, contact us at Cengage Learning Customer & Sales Support, 1-800-354-9706. For permission to use material from this text or product, submit all requests online at www.cengage.com/permissions. Further permissions questions can be emailed to permissionrequest@cengage.com. Unless otherwise noted, all items © Cengage Learning Library of Congress Control Number: 2013957152 ISBN-13: 978-1-285-85965-1 ISBN-10: 1-285-85965-0 Cengage Learning 200 First Stamford Place, 4th Floor Stamford, CT 06902 USA Cengage Learning is a leading provider of customized learning solutions with office locations around the globe, including Singapore, the United Kingdom, Australia, Mexico, Brazil, and Japan. Locate your local office at: www.cengage.com/global. Cengage Learning products are represented in Canada by Nelson Education, Ltd. To learn more about Cengage Learning Solutions, visit www.cengage.com/engineering. Purchase any of our products at your local college store or at our preferred online store www.cengagebrain.com. Printed in the United States of America 1 2 3 4 5 6 7 18 17 16 15 14 Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. To Him who is our source of grace, our source of love, and our source of knowledge, And to Marla, whose love is a source of joy. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Contents Preface Nomenclature 1 Introduction 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 2 29 Fluid Properties................................................ 29 Measurement of Viscosity.................................. 35 Measurement of Pressure.................................... 43 Basic Equations of Fluid Mechanics ................... 48 Summary .......................................................... 67 Show and Tell .................................................. 68 Problems........................................................... 68 Piping Systems I 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 1 The Design Process.............................................. 5 The Bid Process................................................... 9 Approaches to Engineering Design..................... 10 Design Project Example ..................................... 11 Project Management .......................................... 16 Dimensions and Units........................................ 22 Summary .......................................................... 23 Questions for Discussion .................................... 23 Show and Tell .................................................. 25 Problems........................................................... 26 Fluid Properties and Basic Equations 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3 viii xiv 79 Pipe and Tubing Standards................................ 79 Equivalent Diameter for Noncircular Ducts........ 82 Equation of Motion for Flow in a Duct................. 85 Friction Factor and Pipe Roughness.................... 87 Minor Losses ....................................................102 Series Piping Systems ......................................118 Flow Through Noncircular Cross Sections..........125 Summary .........................................................137 Show and Tell .................................................141 Problems .........................................................141 v Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. vi Contents 4 Piping Systems II 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 Selected Topics in Fluid Mechanics 5.1 5.2 5.3 5.4 5.5 5.6 5.7 6 157 The Optimization Process ................................157 Economic Pipe Diameter...................................168 Equivalent Length of Fittings ...........................189 Graphical Symbols for Piping Systems .............194 System Behavior.............................................195 Support Systems for Pipes ................................201 Summary .........................................................202 Show and Tell .................................................203 Problems..........................................................203 Pumps and Piping Systems 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 221 Flow in Pipe Networks.....................................221 Pipes in Parallel..............................................233 Measurement of Flow Rate ...............................239 The Unsteady Draining Tank Problem ..............263 Summary .........................................................272 Show and Tell .................................................272 Problems..........................................................273 287 Types of Pumps ................................................287 Pump Testing Methods .....................................288 Cavitation and Net Positive Suction Head .......299 Dimensional Analysis of Pumps........................303 Specific Speed and Pump Types ........................307 Piping System Design Practices ........................311 Fans and Fan Performance ................................330 Summary .........................................................339 Show and Tell .................................................340 Problems..........................................................341 Group Problems................................................349 Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Contents 7 vii Some Heat Transfer Fundamentals 7.1 7.2 7.3 7.4 7.5 7.6 7.7 8 Double Pipe Heat Exchangers 8.1 8.2 8.3 8.4 8.5 8.6 8.7 9 453 Shell and Tube Heat Exchangers ......................453 Analysis of Shell and Tube Exchangers .............460 Effectiveness-NTU Analysis............................475 Increased Heat Recovery..................................481 Design Considerations......................................485 Optimum Outlet Temperature Analysis............492 Show and Tell .................................................496 Problems..........................................................497 Plate & Frame Heat Exchangers and Cross Flow Heat Exchangers 10.1 10.2 10.3 10.4 10.5 10.6 11 401 The Double Pipe Heat Exchanger .....................401 Analysis of Double Pipe Heat Exchangers.........410 Effectiveness-NTU Analysis............................428 Design Considerations......................................436 Summary .........................................................443 Show and Tell .................................................444 Problems..........................................................444 Shell and Tube Heat Exchangers 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 10 361 Conduction of Heat Through a Plane Wall........361 Conduction of Heat Through a Cylinder Wall...368 Convection—The General Problem....................373 Convection Heat Transfer Problems ..................374 Optimum Thickness of Insulation......................389 Summary .........................................................395 Problems..........................................................395 503 The Plate and Frame Heat Exchanger...............503 Analysis of Plate and Frame Heat Exchangers . .506 Cross Flow Heat Exchangers.............................522 Summary.........................................................537 Show and Tell .................................................537 Problems..........................................................538 Project Descriptions Appendix Tables Bibliography Index 541 607 633 635 Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Preface to the Fourth Edition The course for which this book is intended is a capstone type of course in the energy systems (or thermal sciences) area that corresponds to the machine design course in the mechanical systems area. This text is written for seniors in engineering who intend to practice fluid/thermal design. Fluid mechanics is a prerequisite. Heat transfer is a prerequisite or at least should be taken with this course. Contents The text is organized into two major sections. The first is on piping systems, blended with the economics of pipe size selection and the sizing of pumps for piping systems. The second is on heat exchangers, or, more generally, devices available for the exchange of heat between two process streams. The list of topics that can be added is almost endless. The text begins with an introductory chapter, that provides examples of fluid/thermal systems. A pump and piping system, a household air conditioner, a baseboard heater, a water slide, and a vacuum cleaner are such examples. Also presented are dimensions and unit systems used in conventional engineering practice (i.e., Engineering and British Gravitational systems). The SI unit system is also presented. The student is expected to know about unit systems, which are presented in Chapter 1 to introduce conversion factor tables in the Appendix and to familiarize the reader with the notation in this text. Chapter 1 also contains a description of the design process. A design project example is given, and the steps involved in completing it are presented. These steps include the bid process, project management, construction of a bar chart of project activities, written and oral reports, internal documentation, and evaluation and assessment of results. Chapter 2 is a review chapter on the properties of fluids and the equations of fluid mechanics. This chapter is included to familiarize the student with the tables of fluid properties in the Appendix. This chapter can be omitted from a one semester course if students are confident in their ability to solve problems in fluid mechanics. Viscosity data of various commonly encountered foodstuffs (catsup, peanut butter, etc.) is included to stimulate the student's interest. Chapter 3 is about piping systems. It is expected that by the time students take this course, they will have learned about piping systems in a first course in fluid mechanics. Here, however, the subject of piping systems is covered in greater detail and depth. Specifications for pipes and tubes are discussed. Circular, square, rectangular, and annular cross sections are presented. Laminar and turbulent flow in each of these cross sections is modeled. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Preface ix Chapter 4 begins with a new section on optimization. Various types of problems are covered to illustrate how system optimization is achieved. This provides a lead-in to the economics of pipe size selection, where the least annual cost method is introduced and developed. The next section is on the equivalent length of fittings, presented as an atlernative to the minor loss presentation in Chapter 3. Chapter 4 also contains ANSI standards on how piping systems are to be drawn in isometric views. System behavior, in which flow rate through a given piping system is determined as a function of the driving force, is also presented. Both Chapters 3 and 4 contain modified pipe friction diagrams useful in solving special types of problems. Chapter 5 is on selected topics in fluid mechanics. This chapter begins with a section on flow in pipe networks, focusing specifically on the Hardy Cross method of solution. The next section is on flow in parallel piping systems. Next is a section on the measurement of flow rate in closed conduits where venturi, orifice, turbine-type, variable area, and elbow meters are all described. The chapter continues with equations for modeling unsteady flow in draining tank problems. Chapter 5 is included as a reference chapter and can be omitted in a one semester course. Chapter 6 is about pumps. Types of machines are discussed, and testing methods for centrifugal pumps are presented. Typical charts that one might find in manufacturers' catalogs are described and are used to illustrate the steps in sizing a pump for a piping system. Fans and fan sizing are also discussed. At the conclusion of studying this chapters, an engineer should be able to design an optimized piping system; that is, given a pipe layout and desired flow rate, the student can select the most economical pipe size, pipe material, pipe fittings, pump, hangers, and hanger spacing. Chapter 7 provides an introduction to heat transfer basics in order to present the appropriate heat transfer properties and the heat transfer tables in the Appendix. Conduction and convection are both described, but radiation is not. This chapter is intended as an introduction to heat exchangers which are found in the following chapter. Chapter 7 demonstrates how the general heat transfer problem that includes conduction and convection can be modeled successfully. Chapter 8 is about double pipe heat exchangers. The Log Mean Temperature Difference (LMTD) method is derived and used to analyze existing exchangers. The Effectiveness-NTU method is also derived and used for analysis. Design considerations, namely sizing a double pipe heat exchanger, is covered, and a procedure is developed. Chapter 9 continues with Shell and Tube Heat Exchangers. Again, the LMTD and EffectivenessNTU methods are used to analyze existing exchangers. Also included here are methods used to increase the amount of heat that can be transferred in such exchangers. The optimum water outlet temperature for minimum cost is also presented. Chapter 10 is about the plate and frame heat exchanger, as well as the cross flow heat exchanger. Both of these exchangers are analyzed using Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. x Preface traditional methods. Design considerations are also presented. The emphasis in the heat exchanger chapters is on design and selection. Most chapters contain a section entitled "Show and Tell." Students are asked to provide very brief presentations on selected topics. For example, in Chapter 3, one Show and Tell requires that the student give a presentation on various types of valves that are commonly used. The valves that are available are brought to class and taken apart (or cut in half prior to class) to illustrate how each works. A Show and Tell assignment on this and many other topics is far more effective than a photograph, and gives the student some practice in making an oral presentation. Chapter 11 is an introduction to the projects. The course for which this text is intended requires the students to complete term projects. Each project has associated with it a project description that begins with a few introductory comments and concludes with several tasks that are to be completed. Each project has an estimate of the number of engineers required to finish it in the given school term. The students are responsible for selecting project partners and, as a group, deciding on which projects they would like to work. Each group elects its own project manager or leader. Projects With regard to the projects, the instructor is like a general contractor who has a number of projects/problems that need to be solved. The student groups are like small consulting companies, and it must be decided who gets what project. The awarding of projects is done on a "lowest bidder" basis. All group members earn the same salary (e.g., $55,000 per year or as assigned). All group leaders likewise earn the same salary (slightly more than the group members'). Based on each group's estimate of the number of person–hours required to complete the tasks of the project, a personnel cost is calculated. Other costs include benefits, fees for experts, computer time, and overhead. Each group fills out a bid sheet (see Chapter 1 for an example) for every project that the group is interested in—usually no less than three. The bids are sealed in envelopes, and one class period is spent in a "bid opening ceremony." The lowest bidder for each project then has the option of accepting (or not accepting) that project to work on, keeping in mind that a project for which a group is the lowest bidder might not be the one that group would most like to work on. Each group will then have one project to devote the entire school term to completing. The projects must be managed to ensure that all the work is done before the last one or two weeks of classes, when quality will suffer because of the frantic, last-minute pace. Each group must complete a task planning sheet. Each task is shown on the sheet, along with who is to complete that task and when it is to be completed. Each and every student is to keep a spiral ring (or equivalent) notebook in which everything, from actual design work Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Preface xi to a mere phone call, that the student does on the project and time spent is recorded. The project leaders make sure that the responsible group member completes his/her assigned task on schedule, per the task planning sheet. The task planning sheet can be changed during the school term, but an equitable division of labor must be adhered to and individual tasks must be completed. At the end of the term, students tally their hours and compare the actual cost of completing the project to the estimated cost at time of bid. Project reports are to be given in two forms: written and oral. The written report should detail the solution to all phases of the project as outlined in the original description or as modified in discussion sessions with the instructor. The oral report should summarize the findings and give recommendations; it should be limited in time. It must be emphasized that this text does not provide a complete description in any one area. The objective here is to provide some design concepts currently used by practicing engineers in the area of fluid/thermal systems. The student should remember that actual design details of various systems can be found in textbooks, reference books, and periodicals. Fourth Edition Modifications The fourth edition of this text contains a number of additions and modifications made in response to comments from reviewers. • New information in Chapter 1 includes details on the system approach versus the individual approach to modeling a fluid thermal system. • Chapter 2 additions include viscosity data of non-Newtonian fluids. Chapter 3 is basically unchanged from the second edition except for reorganizing a few sections and topics. • Chapter 4 has an expanded section on optimization in which many example problems have been added. • Chapter 5 has been reorganized, containing information on pipe networks, parallel piping systems, and measurement of flow rate in a pipeline. • Chapter 6 now contains more details on typical pump curves found in catalogs from manufacturers. An expanded section on cavitation has been added. • Chapter 7 contains a review of heat transfer and has been expanded, adding example problems. • Chapters 8, 9, and 10 are basically the same as those in the previous edition. • Chapter 11 provides descriptions of design projects. Many new projects have been added, and an organizational table has been updated. Report writing is discussed in Chapter 1 and is reiterated in this chapter. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. xii Preface Example and practice problems have been added where appropriate, and the end-of-chapter problems are still separated according to sections. The reader can thus easily locate or review problems that relate to a particular topic. A number of design problems have been added. Many topics have been expanded upon, and portions of the text have been reorganized. Instructor's Guide and Solutions Manual An Instructor's Guide and Solutions Manual is available to accompany this text. The Guide provides solutions to the problems in the text and gives a detailed outline of the course. The outline is laid out in a twelve-week plan showing problem assignments, Show and Tell assignments, and project scheduling. The Guide is available to all adopters of the text. Please send a written request on school letterhead to the publisher (Attn: Engineering Editor) in order to obtain your copy. Acknowledgments First Edition: I wish to thank the many individuals, students and faculty alike, who made valuable suggestions on how to improve the text. Moreover, I am greatly indebted to the following reviewers who read over the manuscript and made helpful suggestions: Ray W. Brown, Christian Brothers University; Don Dekker, Rose Hulman Institute of Technology; Gerald S. Jakubowski, Loyola Marymount University; and Edwin P. Russo, University of New Orleans. Second Edition: I wish to thank those individuals who read over the second edition in its formative stages and made many helpful suggestions for improvement: Edward Anderson, Texas Tech University; Don Dekker, Rose-Hulman Institute of Technology; Gerald S. Jakubowski, L o y o l a Marymount University; Ovid A. Plumb, Washington State University; and Gita Talmage, Penn State University. Third Edition: I wish to thank Hilda Gowans at Cengage Learning who was always there with helpful suggestions and guidance when it was needed. I extend my thanks also to the other unnamed individuals at Cengage Learnng who supported this project and who worked toward its completion. I wish to express my gratitude to those individuals who made many helpful suggestions for improvement of the manuscript: Kendrick Aung, Lamar University; Erik R. Bardy, Grove City College; Bakhtier Farouk, Drexel University; A. Murty Kanury, Oregon State University; and Charles Ritz, California State Polytechnic University, Pomona. Fourth Edition: I wish to thank Hilda Gowans and others at Cengage Learning who provided reviews and support for production of this edition. I Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Preface xiii wish to express my gratitude to those individuals who made many helpful suggestions for improvement of the manuscript: Heng Ban, Utah State University, Bakhtier Farouk, Drexel University, Darrell Guillaume, California State University, Los Angeles, Martin Guillot, University of New Orleans, Hisham Hegab, Louisiana Tech University, Kunal Mitra, Florida Institute of Technology, Ron Nelson, Iowa State University, and Steven Pinoncello, University of Idaho. I also wish to extend appreciation to the University of Memphis for providing help with various tasks associated with this project. Finally, I wish to acknowledge the encouragement and support of my lovely wife, Marla, who made many sacrifices during the writing of this edition of the text. William S. Janna Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Nomenclature Unit Symbol A a Cp C Co Cv D D h = 4A/P De D eff F g gc h hc kf L m · m Nu N PT P Pr p Q Qac Qth q q" Definition SI Engineering area m2 ft 2 2 acceleration m/s ft/s2 specific heat J/(kg·K) BTU/(lbm·°R) ratio of capacitances — — orifice coefficient — — venturi coefficient — — diameter m ft hydraulic diameter m ft heat transfer m ft characteristic dimension effective diameter m ft force N lbf gravitational m/s 2 ft/s2 acceleration conversion factor — 32.17 lbm·ft/(lbf·s2) enthalpy J/kg BTU/lbm convection coefficient W/(m 2·K) BTU/(ft 2·hr·°R) thermal conductivity W/(m·K) BTU/(ft·hr·°R) length m ft mass kg lbm mass flow rate kg/s lbm/s Nusselt number — — number of transfer units — — pitch of tube bank m ft perimeter m ft Prandtl number — — pressure Pa = N/m2 lbf/in2 3 volume flow rate m /s f t 3 /s 3 actual flow rate m /s f t 3 /s 3 theoretical flow rate m /s f t 3 /s heat transferred W BTU/hr heat transferred/area W/m 2 BTU/(ft 2 ·hr) (continued) xiv Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Nomenclature xv Nomenclature (continued) Unit Symbol R R R Rh r Ra Re T t U V — V dW/dt Definition SI gas constant — radius m ratio of capacitances — hydraulic radius m radius or radial coord m Rayleigh number — Reynolds number — temperature K or °C time s overall heat W/(m 2·K) transfer coefficient velocity m/s volume m3 power J/s Engineering — ft — ft ft — — °R or °F s BTU/(ft 2·hr·°R) ft/s ft 3 ft-lbf/s or HP Greek Letters α = kf / ρ C p η µ ν = µgc/ρ ρ σ thermal diffusivity efficiency viscosity kinematic viscosity density surface tension m2 /s — N·s/m 2 m2 /s kg/m 3 N/m ft2/s — lbf·s/ft2 ft2/s lbm/ft 3 lbf/ft Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. CHAPTER 1 Introduction Fluid thermal systems is a very broad term that refers to many designs and devices. A pump and pipe combination is an example of a fluid system in which fluid is being conveyed. An air conditioner is a device in which a fluid is conveyed, so it is an example of a fluid system. Moreover, because heat transfer effects are important in the air conditioner, we can consider it a fluid thermal system. For purposes of illustration, suppose that in a food processing operation, one seeks to move peas from one location to a place where they will be packaged and frozen. This feat can be accomplished through use of a freight pipeline. A sketch of such a system is shown in Figure 1.1. Air is moved through a piping system by a fan, and a feed hopper will drop peas into the moving flow of air. The air/pea combination ultimately makes its way to a separator, where the air is discharged, and the peas accumulate. 8 5 6 9 4 2 mixture flow direction 1 3 air inlet 1. blower 2. feed hopper 3. 20 m 4. 7.5 m 5. 10 m 7 10 6. 25 m 7. 15 m 8. 15 m 9. 7.5 m 10. separator FIGURE 1.1. Sketch of a freight pipeline. In designing this system, it will be necessary to know the physical properties of peas: range of diameters, weight of a volume of peas, and their density. It will be necessary to size the pipeline, paying strict attention to regulations regarding health and safety issues (e.g., stainless 1 Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 2 Chapter 1 • Introduction steel must be used for foodstuffs). The fan, the feed hopper, and the separator must be selected. Once the design is completed, hangers and supports for the pipeline have to be selected. The entire design has to be checked and re-checked to be sure that it will work to deliver the volume of peas needed at the separator. Because the investment in such an operation will be sizeable, the overall cost of the system must be kept to an affordable limit. Initial and operating costs, as well as the life expectancy of the installation must also be considered. The design of this unusual fluid system is not trivial, but requires careful planning. These are the concerns of the engineer in designing such a system. Let us next consider an air conditioning, or refrigation unit. Figure 1.2 is a sketch of such a device. The fluid within, known as a refrigerant, undergoes a cycle as it moves throughout the system. The fluid is compressed by the compressor and leaves as a superheated vapor. The vapor enters what is called a heat exchanger (like the radiator of a car). A fan moves atmospheric air over the coils or tubes of the condenser. Heat is transferred from the refrigerant within the tubes to the air outside the tubes. During this process, the refrigerant condenses. The liquid refrigerant next goes to a receiver tank (not shown), where the liquid is separated from any remaining vapor by gravity. Liquid is drawn off from the bottom of this tank and moves through a capillary tube: a long tube of very small diameter. Liquid refrigerant passing through a capillary tube experiences a significant loss of pressure and, correspondingly, a decrease in temperature. The cold liquid refrigerant is then piped to an evaporator, a device similar to the condenser. Air moving past the outside of the evaporator coils loses energy to the refrigerant inside. The refrigerant gains enough energy to vaporize. Once past the evaporator, the refrigerant goes to an acculumator tank (not shown) where liquid and vapor are separated by gravity. Vapor is drawn off from the top of this tank and returned to the compressor. The cycle is repeated. When this system is used to cool the air in a house or a refrigerator, the evaporator is located within the house or refrigerator and inside air is moved past the coils. The condenser and compressor are usually located outside and ambient air is moved past the condenser coils. Thus the refrigerant transfers energy from the evaporator within the house, as well as from the compressor, to the condenser. As indicated in the above discussion, the compressor moves the fluid throughout the system. The fluid itself undergoes a change in phase at places within the system and effects an energy transfer from the evaporator to the condenser. The compressor power must be determined, the fluid conveying lines must be sized, the heat exchangers must be selected, the entire system must be housed, and the fluid itself must be chosen from among many fluids available, requiring strict attention to guidelines regarding the environment. Moreover, the overall cost of the system must be kept to within competitive and affordable limits. Its initial cost, operating cost, Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 1 • Introduction 3 and life expectancy must also be considered. Obviously, the design of this common fluid thermal system is not trivial, but instead requires careful thought and extensive planning. These are the concerns of the engineer in designing such a system. located outside dwelling warm air condenser located within ductwork in the attic of dwelling subcooled condensed refrigerant refrigerant evaporator cool air capillary tube fan one way valve one way valve superheated refrigerant compressor refrigerant vapor FIGURE 1.2. Sketch of an air conditioning unit. Next, consider the operation of a power plant. In conventional systems, steam is produced and passes through a turbine. Downstream of the turbine is a heat exchanger, whose function is to condense the steam to liquid water. The heat from the steam is transferred to water that is taken from a nearby river or lake. However, due to environmental concerns, it may be desired to use a cooling pond rather than a nearby river to dissipate the heat rejected from the system. A cooling pond is a human-made pond, roughly the size of a small lake, that contains sprayers. The sprayers float on the water surface and spray water upward. A portion of the sprayed water vaporizes and transfers heat to the air above the pond. Other modes of heat transfer may also be present. Figure 1.3 shows a plan view of a power plant condenser and a cooling pond. For whatever air temperature exists, it is desired to cool the water to as low a temperature as possible with the cooling pond. Decisions that need to be made include: the amount of heat that is to be rejected, the temperature of the water in the pond as well as the wet bulb temperature of the air, the proximity of the pond to the power plant, the amount of land available for the pond, the size of the pond, the size of the pump required to move water from the condenser to the pond and back, and among other Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 4 Chapter 1 • Introduction from turbine condenser boiler feedwater pump/motor 200 yards cooling pond floating sprayers FIGURE 1.3. Sketch of a cooling pond installation. things the pipe sizes required. The design engineer will make these decisions when designing this fluid thermal system. The freight pipeline, the air conditioner, and the cooling pond are three examples of the many fluid thermal systems that exist and that must be designed. Other examples include: • • • • • • • • • • • A layout of a piping system to deliver ink to various locations in a printing shop. A sand blaster that uses ice instead of sand in order to minimize health hazards and make cleanup easy. A meter that gives an instantaneous reading of miles/gallon for an automobile. A funnel that signals the user to stop pouring before an overflow occurs. A system for recovering heat from a conventional fireplace. A piping system to provide sufficient heat removal to create an ice rink. A system for testing the efficiency of ceiling fan blades. A ventilation system for mines. A device for producing hot lather for shaving. A system useful for measuring thrust developed by a diver who is testing swim fins (or flippers). An apparatus for testing proposed designs of pulsating shower heads. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 1 • Introduction • • 5 The design of an amusement park water slide. The design of a water-oil separation tank to help with cleanup of oil spills. The list can be expanded to include many more examples. Each system requires considerable design work, extensive refining, inevitable redesigning, and an economic analysis. During this process, there will be meetings and discussions, and records will be kept of all deliberations. The objective in this text is to discuss some of the concepts learned in engineering and in economics courses, and to synthesize these concepts into a coherent presentation in which practical applications are given great consideration. Fundamental concepts of fluid mechanics, thermodynamics, heat transfer, material science, manufacturing methods, and economics are combined in order to illustrate how devices and systems are designed. Hopefully, this text will provide the engineer with ideas and design concepts that will enhance his or her future practice. 1.1 The Design Process The design process (ranging from accepting a "job" to producing a final report) involves more than merely finding a solution. So in this section, we will discuss several aspects associated with obtaining a solution to a design project. It is prudent to note that in engineering design work, there may be many possible solutions to a design problem. We will discuss the nature of engineering design, the bidding process, project management, and evaluation and assessment of performance. Nature of Engineering Design The design activity can include looking at drawings, making decisions, gathering information, attending meetings, considering alternatives, and much more. Design is not necessarily a single task but an entire process. An engineer goes through this process to determine how best to use resources to accomplish a required job. Engineers design systems or devices that could be of interest to the public, or to satisfy the desires of a single client. An unfortunate aspect of design is that, in most cases, what the client wants may be unclear to both the engineer and to the client. Problem statements are often filled with uncertainty and are poorly articulated. For this reason a good design engineer will spend considerable time defining the problem and planning the way it will be solved. Work on a project should not be delayed until the last minute when failure to meet an unanticipated requirement leaves no time for correction. Project work requires careful planning and sound management methods. Otherwise, deadlines will be Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 6 Chapter 1 • Introduction missed, and a workable solution may not be obtained. Thus, design involves the use of engineering methods to bring about the "best" change in a poorly understood situation. The change must be brought about with the available resources and by the deadline. One unique feature of design problems is that there is no one "correct answer." For example, in sizing a heat exchanger to provide specific outlet temperatures, one would find that several heat exchangers will work. Each solution will have good and poor design aspects associated with it. A rather large group of interrelated and complex factors must usually be considered, and some good points may have to be neglected to satisfy other needs. The needs that must be considered in a design are referred to as constraints. Besides engineering considerations, constraints can include effects on the environment, effects on the health of individuals who may have to work with the design, economic factors including initial and operating costs, manufacturability, sustainability, and effects of public opinion on the outcome. Design Phases The design process encompasses many phases including: recognizing a need, identifying the problem, synthesizing a solution, re-designing (if necessary) for optimizing the design, evaluating the design, and communicating the results. Figure 1.4 illustrates one (of many) ways that the steps in a design can be synthesized. Design begins when a client recognizes a need and begins working on satisfying that need. The need can be something obvious or merely a sense that something is "not right." Recognition of the need may be triggered by an adverse circumstance. Recognizing a need and identifying or defining the problem are different things. We might recognize the need for cleaner air in a building, and the problem might be an inadequate filtering system. Defining the problem must include all specifications for the system to be designed. This includes its dimensions, characteristics, location, costs, expected life, operating conditions and limitations. Restrictions often encountered include available manufacturing processes, labor skills, materials to be used, and sizes in stock. An optimum solution can be sought once the problem has been defined and its contraints have been identified. Synthesis of the optimum solution requires analysis and optimization. The design must comply with the specifications and if it is not optimum, a re-design is necessary. This part of the process is iterative in nature and continues until the "best" solution is found. Evaluation of the design is a significant aspect of the design process. Evaluation is proof that the design is successful. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.1 • The Design Process 7 Client Public Management Sales Define Need Bid on Project Generate Ideas Select Criteria Identify Limitations Feasible Approaches Formulate Tasks to Perform Formulate Timetable Assign Tasks Progress Reports to Management Work per Schedule Revise Work Plan Maintain Internal Documentation Finalize Design Optimize System Prepare Reports Assess Results and Bidding Process FIGURE 1.4. Design process from defining a need to assessing results. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 8 Chapter 1 • Introduction Communicating the result is the final step in the design process. Communication is done orally and/or by means of a written, detailed report. Presenting the results is a selling job in which the engineer tries to convince the client that this solution is the "best" one. Selling must be done successfully, or the effort is wasted. An engineer who is repeatedly successful in selling results will usually be successful in the profession. An engineer must have effective written and oral communication skills. These include writing, speaking, and drawing, which can be developed and improved with guided practice. A competent engineer should not be afraid of failing to sell an idea. An occasional failure is to be expected, and much is learned from failure. Some great gains can be obtained by someone willing to risk defeat. The real failure is in not trying. A failure in the traditional sense should be viewed as feedback needed to make improvements in a future cycle of designing and selling. In many instances, a rational mathematical approach is abandoned in favor of knowing what the client likes to make selling easier. Using oversized bolts or frames, for example, might create an impression of durability and strength, which is a good selling point. Attractive styling might also be something a client would like to see. While these factors are cosmetic, they should not interfere with the sound operation of the design itself. Codes and Standards A code is a specification for the analysis, design, or construction of something that specifies the minimum acceptable level of safety for constructed objects. For example, each locality has a code for the size of tubing to use in the plumbing of a house. The purpose of a code is to guarantee a certain degree of safety, performance, and quality. Absolute safety is not necessarily assured by a code, but a reasonable level can be met. There are many established standards and codes, enacted by the appropriate authority. Each organization deals with a specific area, such as plumbing, construction, parking lots, and pedestrian walkways. Codes and standards are sometimes established by manufacturers, and sometimes by engineers who work in the industry. Establishment of a code or standard in almost all cases is in response to a perceived need. A standard is a specification for sizes of parts, types of materials, or manufacturing processes. The purpose of a standard is to provide the public or the customer with uniformity in size and quality. A bolt standard, for example, is 1/4-20. All 1/4-20 bolts and nuts have the same thread specifications or standards. There are standards for clothing sizes, paper sizes, wire sizes, shoe sizes, can sizes, furniture sizes, newspaper sizes, as well as bolts and nuts. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.1 • The Design Process 9 Economics Cost considerations play an important role in the design process. Unfortunately, costs are sometimes unpredictable. The designer may have missed a hidden cost. Furthermore, some costs change from year to year depending on the economy of the nation. Cost must be considered, however, as thoroughly as possible in the design process. Using standard sizes is almost a necessity in keeping costs low. A good example is pipe and tubing, both of which are available in discrete sizes. Pumps, motors, fasteners, and the like., are all manufactured to certain standards, and using stock sizes is an excellent idea. Product Safety The engineer should make every effort to ensure that the design is safe and has no defects. An engineer or manufacturer can be held liable for unforseen defects, even those that surface years after the design was finalized. Public safety is the engineer's chief concern. 1.2 The Bid Process The majority of design and construction contracts are awarded through a competitive bidding process. A bid is an offer by a firm (a contractor) to perform work requested by a client (contracting agency). The objective of going through a bidding process is to locate the firm that will do the work for the least cost. There are two major areas to consider: bidding to do work for a private owner, or bidding to do work for the government. The client (or contracting agency) initiates the bidding process by issuing an invitation for bids. In the private sector, the invitation can be in the form of notices sent to individual contractors describing the work to be performed and soliciting bids to complete it. In addition, the contracting agency can place an advertisement in trade journals or in the local newspaper. However governmental solicitations are subject to comprehensive regulations regarding the solicitation of bids. After a contractor has decided to submit a bid, the contractor must determine the cost of completing the work. This may take several weeks of preparation in reviewing specifications, determining the number of personhours required, calculating overhead and profit, and so on. Once complete, the contractor prepares bid documents as required by the client or contracting agency. The bid documents are placed in a sealed envelope or container and submitted to the client, usually by some advertised closing date for bid submission. Bids are opened and reviewed at a bid-opening ceremony. Each contractor who submitted a bid will want to have a representative at the bid opening. Any bid submitted after the closing date can be rejected. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 10 Chapter 1 • Introduction All bids are opened and reviewed by the client or client's agent. The cost estimates are then made public and all contractors will know what has been submitted. In the private sector, the client can select any contractor to do the work regardless of whether the contractor is the lowest bidder. The government, however, is usually bound to grant the contract to the lowest bidder unless there is some justifiably compelling reason not to do so. Exceptions to competitive bidding on the part of the government can exist in a number of circumstances: when it is impractical to have open competition; when only one source and no other supplies services that satisfy the requirements; when there is unusual and compelling urgency; when precluded by agreement; when authorized by law; or when open competition is not in the best interest of the public. Before awarding a contract, it is wise for the contracting agency (client) to review the background of the prospective contractor. Things to consider in trying to determine whether the contractor can successfully complete the job are: • • • • • • • • Is the contractor responsible? Is there a work related legal action against the contractor? Is the contractor financially stable? What ongoing work is the contractor involved in that might cause interference? How has the contractor performed on previous jobs? Can the contractor meet deadlines? Does the contractor have integrity and an ethical standard? Does the contractor have the technical skills to complete the project? Once a bid has been awarded and accepted, the contractor becomes liable for living up to the terms of the contract. In some instances, a contractor may wish to withdraw a bid due to a technical or to a clerical error. There are established procedures for withdrawing a bid or correcting it in these cases. Errors of judgment, however, are not correctable. Such errors include failure to accurately estimate length of performance, overhead costs, profit, and manner of performance. (Information from "Competitive Bidding" by I. Genberg, Construction Business Review, Sept.-Oct. 1993, pp. 31–34.) 1.3 Approaches to Engineering Design There are two approaches to solving a design problem. One is the systems approach and the other is the individual approach. The systems approach involves writing an objective function for the problem at hand. The objective function in engineering problems in some cases is an equation Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.3 • Approaches to Engineering Design 11 for the total cost of a system. The total cost will include an initial cost (for equipment as an example) and operating costs (for electricity or fuel). The initial cost is modified in order to make it an annual cost. Then the annualized initial cost and the operating cost are added to obtain the total annual cost. In a "good" design, we would seek to minimize the total cost, so we would differentiate the total cost expression and set it equal to zero. We would thus obtain an equation that we could solve for a particular parameter. For example, suppose we wish to minimize the cost of a pipeline. We might express all cost parameters in terms of pipeline diameter. We differentiate the total cost expression with respect to diameter and solve for the optimum diameter which is the one that would give us the minimum total annual cost for the system. For a design problem involving many devices, the total cost function can be quite complex. Usually other equations are required in order to solve the differentiated cost equation. These other equations are called constraint equations. They could consist of continuity and energy equations written for every device in the system. Once the objective function and constraint equations are written, we end up with a system of equations that must be solved simultaneously. A number of methods can be used to solve these equations. The systems approach is used in Chapter 4 for pipe sizing. (For a description of the systems approach applied to a number of problems, and solution methods, see Design of Thermal Systems by W. F. Stoecker, McGraw-Hill Co., 2nd ed., 1980.) The other approach to design problems is to consider each device in a system individually. The cost of each device is minimized, thereby minimizing the total cost of the entire system. The advantage of this method is that the equations to solve are simplified. 1.4 Design Project Example We illustrate some of the points made in the preceding sections with an example and some specific ideas. Consider that we are interested in working on a problem that involves the recovery of waste heat in a manufacturing facility. The problem is stated as follows. Heat Recovery in a Sheetrock Plant One of the components needed in the manufacture of sheetrock is water. The process requires 70 gpm of water at a temperature of about 85˚F. During summer months, the city water supply provides water whose temperature can be as high as 90˚F. During other months, the average temperature of water supplied by the city is about 45˚F. This water must be heated so that Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 12 Chapter 1 • Introduction it can be used successfully for the process. The water is heated by natural gas burners while it is in a storage tank. One of the final phases of sheetrock production is the drying stage. Heated air is moved by a fan around the sheetrock in an oven. The air is then exhausted. It is desired to recover energy from the warm, humid exhaust air and use the energy to pre-heat the incoming city water from 45˚F (worst case) to as warm as possible. The energy recovered would reduce the need for natural gas to be used as the main heating medium. Conditions indicate that the heat recovery system will be in operation for 24 hours per day (six days per week) for eight months. Figure 1.5 shows the position of the drying oven and of the holding tank. As shown, the water tank is 300 ft from the oven. Suppose that this Heat Recovery Project arises in a plant that does not have enough engineers available to work on it. Management has decided to allow an outside engineering consulting company to solve the problem or at least to see if it is cost effective. Management will contact any number of consultants and invite them publicly to bid on the project. That is, each consultant is invited to submit to management (the client in this example) a proposal that outlines what is to be done and how much the consulting company will charge to perform only the design work. Actual construction or installation might also be part of the bid, depending on what the client requests of the bidders. 3.6 ft ID aluminum stacks 16 ft 4 ft water holding tank 30 ft drying oven 300 ft gas burners city water line, p = 55 psig FIGURE 1.5. Layout showing drying oven and holding tank. "Our" company has been invited to submit a bid to do the design work on this project. Before we can prepare a bid, however, we must have some idea of what needs to be done. So we review the problem statement assuming Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.4 • Design Project Example 13 that it is all we have been given by the client. We examine a number of things with reference to the comments made earlier. Insufficient Information The problem statement seems clear enough, but there is information which is missing that we will need. At first glance, we might wish to place a heat exchanger in each stack. To size the heat exchangers, however, we must know the temperature of the exhaust gases in the stacks and the flow rate of air through them. The client might have no idea what these are, and we may be required to have access to the roof, taking a thermocouple, a digital thermometer, a pitot-static tube and a differential pressure meter. We need to know the ceiling height between the holding tank and the stacks, in case we wish to install the pipe with hangers along the ceiling, or along a wall, rather than on the floor. In order to perform an economic analysis, we must have information on the natural gas usage and city water temperature on a monthly basis for at least one (and preferably three) years. Certainly, there is insufficient information at this point, and one possible reason for this is that the person(s) providing the problem statement do not know what an engineer needs to solve it. No Unique Solution Our company might design a system having one heat exchanger in only one stack. Another company might propose a heat exchanger in each stack. A separate fluid system containing ethylene glycol and water could be used to transfer heat from a heat exchanger in the stack to water in the holding tank. Alternatively, city water can be run to the heat exchanger in the stack first and then to the holding tank. Obviously this design problem has many solutions. Constraints Finding the "best" solution to this problem from the many that will work is a matter of trying out several (on paper) and determining which satisfies the constraints. Does the client wish to save as much money as possible by installing this system? Has the Environmental Protection Agency put a limit on the temperature of exhaust gases from this facility? The objectives and constraints need to be identified. Submitting a Bid We have decided that our company has the required expertise, time, and skill to solve this problem, and now we would like to submit a bid. We Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 14 Chapter 1 • Introduction must consider more specifically the tasks involved. We have obtained the additional information we need from the contracting agency. It is apparent that we have to design the piping system from the tank to one of the stacks and back. We have to specify a pipe size, determine the routing of the line itself, select a pump for the job, and size a heat exchanger to place in one of the stacks. More specifically, the things that must be completed are: l . Appropriate heat exchanger type, size, and material of construction. 2. Pump (if necessary) size, location, and material of construction. 3. Piping, pipe fittings, size, routing, and material. (Consider that a flowmeter and/or pipe insulation may be desirable.) 4. Total cost of system including installation, operation, and maintenance. 5. Payback period on the investment. 6. Use stock sizes everywhere possible. 7. Investigate local codes and adhere to them. 8. Analyze the system for safety considerations. This list of items makes up the engineering phase of the project, which is only a small portion of the entire design process. Bidding We have identified what we think needs to be done, based on our concept of how this problem should be solved. It may have taken several days to draw up preliminary sketches, attend meetings, visit the plant, and so on. We are now ready to prepare our bid documents. In many cases, these documents are provided by the client and we merely fill them out. In some cases, however, each bidder can complete an in-house form and submit that to the client. In this example, suppose we are working with a very simplified form such as that in Figure 1.6. Note carefully what is requested on this form. First, the project title is required along with an estimated bid amount. The estimated bid amount is calculated by completing this form. Notice that there is a column appended to this form labeled "Actual." This column is added for internal record-keeping and would not be submitted to the client. We must remember that this bid is to be submitted by the closing date which appears on the second line of the bid sheet. The due date is when we agree to have our work completed. The hours required to complete it is our estimate of the person-hours that must be devoted to the project. The list of persons in the design group who will work on this project is given in Part A along with person-hours and salary. At best, the number of person-hours is an estimate, but an experienced bidder can make an accurate appraisal. Fringe Benefits for each employee working on the project are paid directly from the project budget. These include insurance, medical benefits, Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.4 • Design Project Example 15 Estimated Bid Amount Title of Project Closing Date Due Date Project Director A. Personnel Name Actual Hrs Req'd to Complete Telephone Person-hrs Salary 1. $ $ 2. $ $ 3. $ $ 4. $ $ 5. $ $ 6. Subtotal $ $ B. Fringe Benefits (35% of A.6) $ $ $ $ C. Total Salaries, Wages, & Fringe Benefits (A.6 + B) D. Miscellaneous Costs 1. Materials & Supplies $ $ 2. Other $ $ 3. Subtotal $ $ E. Travel F. Consultant Services 1. $ $ $ $ $ $ 3. Subtotal $ $ G. Total Direct Costs (C + D.3 + E + F.3) $ $ H. Indirect Costs (50% of G) $ $ I. Amount of this Bid (G + H) $ $ 2. Signatures of Engineers Date Initials 1. 2. 3. 4. 5. FIGURE 1.6. Example of a budget-bid sheet. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 16 Chapter 1 • Introduction retirement benefits, and the like. Miscellaneous Costs (including materials, supplies if a model is to be built, etc.) are charged to the project. Travel by the group (to the facility for example) is charged to the project. It may be necessary for the design group to use the services of an expert (Consultant Services) and payment to the expert for his or her services is also charged to the project. The Indirect Costs (including overhead to pay for utilities, office space, secretarial help, profit, etc.) are also a part of the project cost. The total of these items is the cost that we, the contractor, propose to charge the client to complete the design—not to build it, but merely design it. Note that most of the items are tied directly to the person-hours estimated in the beginning, so an accurate estimate is highly critical. 1.5 Project Management Suppose now that the Heat Recovery Project has been awarded to us because our company is the lowest bidder (or because we personally know the plant manager!). Completion of the job requires an organized and wellmanaged effort. The project must be divided into several smaller jobs that are finally synthesized into the overall solution. This phase involves identifying the smaller jobs, assigning the completion of each small job to an individual or individuals, and requiring each small job to be completed at a certain time. This breakdown can be done by the Project Manager or Project Director, who is ultimately responsible for ensuring that the job is finished on time and within budget. Thus, a Project Director must be selected at this point, and his or her job will be to manage the personnel in the group so that they complete the project on time. It is convenient for the Project Director to compose a bar chart of project activities that outlines the tasks, or smaller jobs, to be performed in completing the projects. The bar chart is much like a graph in which time is laid out on a horizontal axis and project activities appear on the vertical axis. The advantages of such a layout are that all activities are mapped out and assigned, that the order of the activities can be readily seen, and that an overall readable picture with the expected completion time is on hand. One disadvantage of such a chart is that it will probably need updating, which can require much time. A bar chart for the Heat Recovery Project is shown in Figure 1.7. It is a "first draft" that includes all of the tasks that we could identify. They are listed as activities in order on the left. The chart shows which activities or tasks require the completion of another task beforehand. The entire project is mapped out over an eight-week period with estimates of how long each activity will take. Also, letters appearing in each shaded rectangle represent the initials of the engineer(s) who is (are) responsible for completing the corresponding task. The shaded rectangles are connected Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.5 • Project Management 17 Week Number Activity 1 Select Line Size MS Determine Route of Pipe MS Analyze and Select Heat Exchanger DB Select Pump Perform Economic Analysis Produce Layout Drawings Write Report 2 3 4 5 6 7 8 Heat Recovery in a Sheet Rock Plant EL DB MS EL MS DB EL Design Group: Marianne Schwartz, David Birdsong, Ed Lin FIGURE 1.7. Bar chart of small jobs to perform in completing the Heat Recovery Project. with lines and arrows that indicate a succession of events. Thus, before a pump is selected, for example, the line size, its route, and the heat exchanger must first be specified. Suppose that after some time has passed, we think of (or are assigned) several other tasks to perform, or some tasks were completed before their target completion date. It is advisable to rework the chart to add the new event(s), assign a responsibility to it (them), and update the completion of the finished smaller jobs. Suppose also that it appears as if the project will be finished earlier (or later) than what was originally scheduled. This is brought out in the modified chart as well. Say that after much study, we find we must use an exchanger in both stacks in order to recover the required energy. Figure 1.8 shows a modified chart. Note that the new activities have been added in the appropriate positions showing their relationship to other tasks. The Project Director is also responsible for handling the budget allowed for completion of the project. This would include signing all requests for payment and keeping track of how the project budget funds are expended. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 18 Chapter 1 • Introduction Week Number Activity 1 Select Line Size MS Determine Route of Pipe MS Select Heat Exchanger 1 DB EL Select Heat Exchanger 2 DB EL Select Pump Perform Economic Analysis Produce Layout Drawings Write Report 2 3 4 5 6 7 Heat Recovery in a Sheet Rock Plant DB MS EL MS DB EL Design Group: Marianne Schwartz, David Birdsong, Ed Lin FIGURE 1.8. Modified bar chart of small jobs performed in the Heat Recovery Project. The Project Director will meet frequently on an as needed basis with the group members to offer assistance if necessary. Project management has been the subject of much study. As a result, it has been found that some of the more important tasks of a design group relate to how the group members interact or deal with each other, rather than how the engineering work is completed. People skills, like technical expertise, require continual refining. With regard to these comments, it is prudent to remember that the primary functions of the Project Director and the group members are as follows: • Always keep in mind the objective of the entire project, • Know exactly how each group member will contribute to the overall success of the design effort (i.e., each group member will know without question exactly what his/her responsibility is), • Identify any and all obstacles that prevent a group member from completing a task, • Remove the obstacles, Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.5 • Project Management • 19 Remember that all group members are "being paid" to maintain an effective working relationship with the others. To these ends, the Project Director should schedule regular meetings of the group and should prepare extensive minutes of the meeting. Minutes should include extensive details, such as the agenda and who is responsible for presenting information. The Project Director should also prepare oral and/or written progress reports on a weekly basis for the client. The client must be kept informed regularly on the progress being made. Internal Documentation The design process described above listed various activities that will eventually result in a report. The report is then provided to the client. The consulting company, however, will need to keep on file much more information about the project than is included in the written report. Once an engineer begins work on a project, the engineer is to obtain a notebook and keep track of all things performed in association with the project (in ink), especially including dates and time spent. Even the most seemingly trivial contribution (such as a phone call) should be recorded. Nothing is to be erased or eradicated from the notebook. The notebook should also contain all the engineering work and calculations done on the project. The notebook is a diary. Errors are "removed" from the diary by drawing a straight line through them but they must still be readable. Each member of the group will have his or her own notebook for each project. The progress made by the group member can be ascertained by reviewing his or her diary. The copy of the final report that stays within the consulting company files should contain the budget-bid sheet originally submitted. At the time that the project is finished, the column labeled "Actual" on the budget-bid sheet is completed to show the actual costs of items requested as part of the project. These include the person-hours expended and the profit earned on those person-hours. Remember that we are in "business" to make money and that performance on the project will be evaluated in proportion to the actual profit realized. The engineers' notebooks, final report, and completed budget-bid sheet make up the documentation that the consulting company will want to keep on file for future reference. Should the project need to be reviewed in the future, the necessary details will be available. The Reports Next, suppose that the engineering phase of the project has been completed and it is now necessary to communicate the results. Usually a written report and an oral presentation are given by the consultant to the Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 20 Chapter 1 • Introduction client. The written report will contain several items; a suggested example format is given in Figure 1.9. Each item is described as follows: Letter of Transmittal—Written to the client stating that the project has been completed and that the results are presented in the accompanying report. Title Page—Lists project title, finished project due date, engineers who worked on the project, and the name of the consulting company. Note that all pages of the report need to be numbered, dated, and identified somehow with the consulting company. Problem Statement—Reiterates succinctly the problem, included so that all concerned will know what project was completed. Summary of Findings—Summarizes the details of the solution. This section might present a list showing, for example, and what pump to buy, what line size to use, where to route the pipe, what heat exchanger to use, suggested suppliers, and costs for all components. Drawings of the system would also be included. The summary should be complete enough so that the client could submit it to a contractor who could complete the installation of all components. Bibliography Reference Materials Narrative Table of Contents Summary of Findings Problem Statement Title Page Letter of Transmittal FIGURE 1.9. Elements of the written report. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.5 • Project Management 21 Table of Contents—Refers the reader to any section of the report. Narrative—Presents the details of all components specified in the summary and why each component was selected. For example, the details of how the pump was selected would be included here. Enough written detail must be included so that the reader can follow every step of the development. The organization of the narrative and titles of all sections will vary from writer to writer. However: If your audience has read your report and does not understand all that you wrote, then you have not expressed yourself clearly enough. Write for the audience. Bibliography/Reference Materials—Shows text titles and publications used to arrive at the specifics of the design. This section should also include information from catalogs of suppliers, such as pump performance curves, if appropriate. The written report should appear professional in every way. A wellwritten presentation will show that the writer is meticulous and convince the client that a great deal of care went into completing the job. Text, graphs, drawings, and charts are done by computer with nothing drawn freehand. The entire report should be bound, and the client should be provided with more than one copy. The oral report should be short and it need not be detailed. The oral report consists of the problem statement and a summary of the findings, which includes initial and operating costs. If questions arise, the presenter can refer to details found in the narrative. Therefore, the presenter should be prepared to give details of the entire study but present only the problem statement and the summary. Evaluation and Assessment of Results The work performed on a project must be evaluated if possible. The two items of importance are: Will the system work as designed, and have we made a profit by delivering a good product? In some cases, the client will not construct the system for a number of months or even years. Moreover, it is unlikely that the installed system will contain the necessary instrumentation to evaluate performance (e.g., thermocouples, flow meters, etc.). Even after installation, it may take years to determine if the system works as designed. In the Heat Recovery Project of this chapter, it is necessary to wait for one year after installation to see if there is any savings in natural gas expenditures. Suppose that the system for some reason does not work as designed and some of those who worked on it do not remember all of the details, or have Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 22 Chapter 1 • Introduction accepted employment elsewhere. We can refer to the saved diaries of the engineers and work with the client appropriately to correct the problem. Whether a good product was delivered might never be assessed. Profit realized can be assessed, however, and is usually measured by an elaborate accounting system outside the scope of engineering. It will become evident that the engineering phase of any project requires a relatively minor amount of total time expended. Equally important is the time and effort spent in documenting activities and especially in communications. 1.6 Dimensions and Units The unit systems used in this text are primarily the British Gravitational, the Engineering or U.S. Customary system, and the SI unit system. Fundamental dimensions and units in each of these systems are listed in Table 1.1. Also shown are dimensions and units in other systems that have been developed, namely, the British absolute and the CGS absolute. When using U.S. Customary units, a conversion factor between force and mass units must be used. This conversion factor is gc = 32.2 lbm·ft lbf·s 2 (U.S. Customary) (1.1) In the other unit systems listed in Table 1.1, the conversion g c is not necessary nor is it used. The equations of this text will contain gc, and if U.S. Customary units are not used, the reader is advised to either ignore gc or set it equal to gc = 1 mass unit·length unit force unit·time unit2 (Other unit systems) (1.2) When solving problems, a unit system must be selected for use. All equations that we write must be dimensionally consistent. Therefore all parameters we substitute into the equations must be in proper units. The proper units are the fundamental units in each system. With the huge volume of parameters that have acquired specialized units (e.g., horsepower, ton of air conditioning, BTU, tablespoon, etc.), we see that the process of converting to fundamental units is a never-ending but ever-present necessity. To ease this burden, Appendix A provides a set of conversion factor tables as well as prefixes that are used when working in SI units. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.7 • Summary 23 TABLE 1.1. Conventional unit systems. SI Engineering British Absolute CGS Absolute Mass (M) (fundamental) kg l bm l bm gram Force (F) (derived) N poundal dyne Dimension Mass (M) (derived) British Gravitational slug Force (F) (fundamental) lbf Length (L) ft m ft ft cm Time (T) s s s s s °R °F K† °C ·R °F °K °C — — °R °F lbm·ft 32.2 lbf·s2 — — Temperature (t) Conversion Factor gc lbf †Note that in SI, the degree Kelvin is properly written without the ° symbol. 1.7 Summary In this chapter, we have examined some fluid thermal systems and indirectly defined them. We have also discussed the design process, including the nature of design, design phases, codes and standards, economics, product safety, and the bid process. Furthermore, we have described project management methods, as well as report writing and evaluation of results. These topics are amplified in the questions and problems that follow. We also briefly discussed unit systems including SI, U.S. Customary, and British Gravitational systems. Mention was made of some specialized units that have arisen in industry and that fundamental units should be used when solving problems. 1.8 Questions for Discussion The following questions should be addressed by groups of four or five individuals who spend 10 minutes on each assigned question. At the end of the discussions, the conclusions should be shared with the other groups in the form of a three-minute or shorter oral report. 1. Discuss the properties of a plastic that is to be used for cassettes or CDs. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 24 Chapter 1 • Introduction 2. What factors influence the decision on how large to make a hand calculator? 3. What are the desirable properties of a material used as a bathtub? 4. Discuss the desirable properties of a tube or tubes used in a solar collector. The tubes are to convey water that is heated by the sun. 5. What are the desirable properties of a material that is to be made into an inflatable float for people to use at a swimming pool? 6. What are the desirable properties of an automobile bumper that can withstand the impact of a 5 mph accident? 7. What should be the properties of a material used as brake lining in a conventional automobile? 8. Discuss the factors that contribute to the decision on how much weight a ladder should be able to support and what material it should be made of. 9. Discuss the factors that contribute to the decision on how tight a manufacturer should make the threaded top on a jar of mayonnaise. 10. Silverware refers generally to eating utensils. However, certain types of such utensils are made of silver and other types made of stainless steel. Which of these materials is the better choice for producing eating utensils? Why? 11. What are the expected properties of a paint that is used on streets as a lane marker? 12. Discuss the properties of a material that is to be used for a balloon—the inflatable type that would be used for parties. 13. Discuss the desirable properties of a tank that is to be used to store liquid oxygen. 14. How long should the soles of dress shoes last? What should be the properties of shoe soles? 15. Is it always appropriate for a job to be awarded to the lowest bidder? List exceptions and give reasons why or why not. Is it fair for a contractor to be awarded a bid merely because he "personally knows the plant manager"? Is it necessary to be fair in the private sector? Is it necessary to be fair when the government is involved? Define "fair." 16. Should profit always be a motive in the consulting business? 17. Consider the question "Have we made a profit by delivering a good product?" Define a "good" product with regard to the Heat Recovery Project. 18. A manufacturer of vacuum cleaners says his product is "twice as good" as any on the market. With regard to this claim, Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.8 • Questions for Discussion a. b. 25 Determine how to evaluate the performance of vacuum cleaners, taking into account as many factors as appropriate. Determine in what way a vacuum cleaner can be "twice as good" as another, if possible. 19. What makes a detergent "better" than that marketed by other companies? How would you evaluate the performance of laundry detergent? What makes a laundry detergent "good"? In very specific terms, describe how a detergent can be "better" than another. Does this mean that the detergent cleans "twice as good" as another? If so, what does "twice as good" mean in this context? 20. Car wax is an interesting product and is avalable from many manufacturers. You want to check out a car wax before you make a buying decision. What makes a car wax "better" than any other? Determine how to evaluate a car wax. That is, what makes a car wax a "good" car wax? 21. You have been contacted as an expert by a college friend who has gone into business for herself. She is a chemist and is making and marketing hair color products. She believes she can enlist your expert services for a reasonable fee. She wishes to claim that the hair color product she makes is "better" than any other on the market. She would like you to help plan a testing program. Determine how to evaluate a hair color and a way to conduct a testing program. What are the desirable properties of a substance marketed as something to use to color hair? 22. Determine how to evaluate a chemical that imparts "stain resistance." What is stain "resistance" versus something that does not stain at all? Determine a testing program for defining and evaluating stain resistance. Would a number scale be appropriate for such chemicals? 23. You wish to determine how effective certain color combinations are with respect to human eyesight and reaction times. Data on this sort of thing is important to sign companies and to the government when making signs to help signal motorists. For example, is black lettering on a white background better than yellow on green? If signs are made with these (or other) color combinations, which of them will be recognized more quickly by an observer? Determine a testing method to measure color contrast that can be used on signs having various color combinations. 1.9 Show and Tell The answers to the following questions should be addressed and presented by individual students in the form of an oral report. 1. What instrumentation is necessary in the Heat Recovery Project if an evaluation of system performance is to be conducted? Explain the function of each instrument and what calculations need to be made using them. 2. What are the human safety factors that should be considered in the Heat Recovery Project of this chapter? Is there a local safety code? 3. Obtain a set of bid documents from a contractor or a contracting agency. Give a presentation on the items contained. 4. Locate a local code that applies to plumbing or electrical work. Give a presentation on what it contains. 5. Give several examples of standards used in industry. Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 26 Chapter 1 • Introduction 1.10 Problems Conversions and Unit Systems 1. Consult an appropriate source to determine the conversion factors associated with the following conversions: a. number of dashes per teaspoon b. number of teaspoons per tablespoon c. number of tablespoons per cup d. number of cups per quart e. number of quarts per gallon 2. Consult an appropriate source to determine the meaning of the following units (remember to look up the proper pronunciation as well): a. coomb b. scruple c. cord of wood d. ream of paper 3. Consult an appropriate source to determine the meaning of the following units: a. gill b. degree-day c. ton versus metric ton d. long ton versus short ton 4. How many "hins" are in a "bath"? How many "baths" are in a gallon? 5. What is the relationship between an ounce (16 ounces per pound) and a fluid ounce (16 ounces equals one pint)? 6. What is the origin of the "horsepower"? Why would anyone wish to express power in the unit of horsepower? How many watts are in one horsepower? 7. The unit for volume flow rate is gallons per minute, but cubic feet per second is preferred. Use the conversion factor tables in Appendix A to obtain a conversion between these two units. 8. Which is heavier—a grain or a dram? Express both in the appropriate English fundamental unit. 9. How many years does a furlong designate? Furthermore, if a furlong is a linear measurement, what does this have to do with "years"? Why? 10. What is the difference between troy weight and avoirdupois weight? Express a pound in each of these systems in terms of grains. 11. Is something called a "log" a unit of measure for liquid or dry goods? What is the conversion between a log and the appropriate SI unit? 12. In the plastics industry, what is a gaylord? 13. A shotgun gauge refers to what dimension of the firearm? Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Section 1.10 • Problems 27 14. Nine gage wire and eleven gage wire are both used extensively in making chain link fence material. What are the diameters of these wires? What other wire diameters exist, and what is the standard used in sizing wires? 15. Sheet metal screws are sized according to what standard? What is the difference between a machine screw and a sheet metal screw? Measurement Scales 16. What is the Forel Ule scale used to measure? 17. What is the Snellen Fraction? 18. The Scoville Unit is a measure of what? 19. What is the Shore Hardness scale used to measure? 20. The Shade number is used as a measure of what? 21. The Beaufort scale measures what? 22. What scale is used to measure the "strength" of an earthquake? What is actually being measured? 23. What is the Numeric Rating Scale (NRS-11) used to measure? 24. To what does "Carat Purity" refer? 25. Canned foods are quite common. How are can sizes measured or expressed by can manufacturers? What are the differences in can size specifications used in the United States.? What is used in the metric system? Miscellaneous Measurements 26. Why is a mile 5 280 ft? 27. By what must a quart be multiplied to obtain a bushel? 28. What is a "hat trick"? 29. How long is the circumference of a racetrack; i.e., how many laps must be made in a one mile race? 30. What is the significance of an acre, and how many square feet are contained in one? Which is larger, an acre or an arpent? 31. What is the definition of the body mass index? What is yours? 32. How many barleycorns are in an inch? 33. How m

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