Grado Ingenieria Electrica

Chapter 1 Introduction and Basic Concepts

Solutions Manual for Fluid Mechanics: Fundamentals and Applications by Çengel & Cimbala

CHAPTER 1 INTRODUCTION AND BASIC CONCEPTS

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Chapter 1 Introduction and Basic Concepts Introduction, Classification, and System

1-1C Solution

We are to define internal, external, and open-channel flows.

Analysis External flow is the flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe. The flow in a pipe or duct is internal flowif the fluid is completely bounded by solid surfaces. The flow of liquids in a pipe is called open-channel flow if the pipe is partially filled with the liquid and there is a free surface, such as the flow of water in rivers and irrigation ditches. Discussion As we shall see in later chapters, there different approximations are used in the analysis of fluid flows based on their classification.1-2C Solution

We are to define incompressible and compressible flow, and discuss fluid compressibility.

Analysis A fluid flow during which the density of the fluid remains nearly constant is called incompressible flow. A flow in which density varies significantly is called compressible flow. A fluid whose density is practically independent of pressure (such as a liquid) is commonly referredto as an “incompressible fluid,” although it is more proper to refer to incompressible flow. The flow of compressible fluid (such as air) does not necessarily need to be treated as compressible since the density of a compressible fluid may still remain nearly constant during flow – especially flow at low speeds. Discussion It turns out that the Mach number is the critical parameter to determinewhether the flow of a gas can be approximated as an incompressible flow. If Ma is less than about 0.3, the incompressible approximation yields results that are in error by less than a couple percent.

1-3C Solution

We are to define the no-slip condition and its cause.

Analysis A fluid in direct contact with a solid surface sticks to the surface and there is no slip. This is known as theno-slip condition, and it is due to the viscosity of the fluid. Discussion There is no such thing as an inviscid fluid, since all fluids have viscosity.

1-4C Solution We are to define forced flow and discuss the difference between forced and natural flow. We are also to discuss whether wind-driven flows are forced or natural. Analysis In forced flow, the fluid is forced to flow over a surface or ina tube by external means such as a pump or a fan. In natural flow, any fluid motion is caused by natural means such as the buoyancy effect that manifests itself as the rise of the warmer fluid and the fall of the cooler fluid. The flow caused by winds is natural flow for the earth, but it is forced flow for bodies subjected to the winds since for the body it makes no difference whether the air...