InTech

SEP-OCT 2018

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Reestablishing equilibrium The phenomenon of flow in conduits (pipes) is best thought of as an attempt to reestablish an equilibrium state in a fluid constrained by conduit walls. In a closed system under pressure, when all valves are shut, all forces are accompanied by equal and opposite forces. The fluid is stationary. In an open system, when valves are open, there is an imbalance of forces, and the fluid moves in a direction that will reestablish equilibrium. If mass and energy are added continuously to an open system, flow will be continuous. The mass added could be water flowing to a res- ervoir behind a dam, or water pumped to a head tank. Once there, the water has energy by virtue of its position. This energy is potential energy or the potential to do work. Upstream of a closed tap, faucet, or valve, the water will be subject to the weight (force) of the water above it. It will exert a pressure (force per unit area) to equilibrate this force. This pressure is the result of repulsion aris- ing when molecules approach one another. The pressure is associated with a static fluid and with a form of energy called static energy. INTECH SEPTEMBER/OCTOBER 2018 51 of incompressible fluids It is not necessary to have a higher pressure upstream in order to initiate flow. Flow of Industrial Fluids–Theory and Equations provides context—both theoretical and practical— to all who wish to understand fluid flow. The book's purpose is to link fluid flow theory to practice in sufficient detail to give readers understanding of both theory and practice. The theoretical detail is limited to that necessary to understand practical problems—to the application of equipment and devices, not to their design. Insight is the primary goal. Basic theory and equations of fluid flow are given in an understand- able but not overly simplified manner. To satisfy a broad intended audi- ence, the book has a parallel structure of chapters and appendices. The chapters contain a logical, common sense description of the concepts and the equations of fluid flow. The appendices contain detailed derivations of the equations and detailed explanations of the subject matter of the cor- responding chapters. More than 60 illustrations and 20 tables graphically represent data and ideas and allow the reader speedy access to precise data. Technical caveats found throughout the book also encourage the reader to pay particular attention to specific topics and thus avoid costly errors or misunderstandings. Many texts deal with instruments to measure and control the flow of fluids. They describe how devices work and only discuss fluid mechanics and dynamics incidentally. This text takes a different approach and is intended to be complementary to the above-mentioned ones. It discusses fluid flow in a way that gives the reader a clear grasp of the fundamentals that affect his or her work. The fundamentals are then linked to entire fluid systems. Flow of Industrial Fluids – Theory and Equations is available at the ISA bookstore at www.isa.org/store/flow-of-industrial-fluids-theory-and- equa tions/116438. ABOUT THE BOOK AUTOMATION BASICS

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