Chapter 1 - The break-up of a fluid jet into drops is a...

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Unformatted text preview: The break-up of a fluid jet into drops is a function of fluid properties such as density, viscosity, and surface tension. [Reprinted with permission from American Institute of Physics (Ref. 6) and the American Association for the Advancement of Science (Ref. 7).] Fluid mechanics is that discipline within the broad field of applied mechanics concerned with the behavior of liquids and gases at rest or in motion. This field of mechanics obviously encompasses a vast array of problems that may vary from the study of blood flow in the capillaries 1 which are only a few microns in diameter 2 to the flow of crude oil across Alaska through an 800-mile-long, 4-ft-diameter pipe. Fluid mechanics principles are needed to ex- plain why airplanes are made streamlined with smooth surfaces for the most efficient flight, whereas golf balls are made with rough surfaces 1 dimpled 2 to increase their efficiency. Nu- merous interesting questions can be answered by using relatively simple fluid mechanics ideas. For example: n How can a rocket generate thrust without having any air to push against in outer space? n Why can’t you hear a supersonic airplane until it has gone past you? n How can a river flow downstream with a significant velocity even though the slope of the surface is so small that it could not be detected with an ordinary level? n How can information obtained from model airplanes be used to design the real thing? n Why does a stream of water from a faucet sometimes appear to have a smooth surface, but sometimes a rough surface? n How much greater gas mileage can be obtained by improved aerodynamic design of cars and trucks? The list of applications and questions goes on and on—but you get the point; fluid mechanics is a very important, practical subject. It is very likely that during your career as an engineer you will be involved in the analysis and design of systems that require a good understanding of fluid mechanics. It is hoped that this introductory text will provide a sound foundation of the fundamental aspects of fluid mechanics. 3 1 I ntroduction Fluid mechanics is concerned with the behavior of liquids and gases at rest and in motion. One of the first questions we need to explore is, What is a fluid? Or we might ask, What is the difference between a solid and a fluid? We have a general, vague idea of the difference. A solid is “hard” and not easily deformed, whereas a fluid is “soft” and is easily deformed 1 we can readily move through air 2 . Although quite descriptive, these casual observations of the differences between solids and fluids are not very satisfactory from a scientific or engineering point of view. A closer look at the molecular structure of materials reveals that matter that we commonly think of as a solid 1 steel, concrete, etc. 2 has densely spaced molecules with large intermolecular cohesive forces that allow the solid to maintain its shape, and to not be easily deformed. However, for matter that we normally think of as a liquid not be easily deformed....
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This note was uploaded on 04/17/2008 for the course ME 111 taught by Professor Usaxena during the Spring '08 term at San Jose State.

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Chapter 1 - The break-up of a fluid jet into drops is a...

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