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Unformatted text preview: Chapter 10 Introduction to Fluid Mechanics Chapter 10 INTRODUCTION TO FLUID MECHANICS Classification of Fluid Flows 10-1C The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe is external flow . The flow in a pipe or duct is internal flow if 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. 10-2C A fluid flow during which the density of the fluid remains nearly constant is called incompressible flow . A fluid whose density is practically independent of pressure (such as a liquid) is called an incompressible fluid. The flow of compressible fluid (such as air) is not necessarily compressible since the density of a compressible fluid may still remain constant during flow. 10-3C A fluid in direct contact with a solid surface sticks to the surface and there is no slip. This is known as the no-slip condition , and it is due to the viscosity of the fluid. 10-4C In forced flow, the fluid is forced to flow over a surface or in a 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 motion is caused by a fan or by the winds. 10-5C The pressure of a vapor, whether it exists alone or in a mixture with other gases, is called the vapor pressure P v . During phase change processes between the liquid and vapor phases of a pure substance, the saturation pressure and the vapor pressure are equivalent since the vapor is pure. 10-6C Yes. The saturation temperature of a pure substance depends on pressure. The higher the pressure, the higher the saturation or boiling temperature. 10-7C If the pressure of a substance is increased during a boiling process, the temperature will also increase since the boiling (or saturation) temperature of a pure substance depends on pressure and increases with it. 10-8C During liquid flow, vaporization may occur at locations where the pressure drops below the vapor pressure. The vapor bubbles collapse as they are swept away from the low pressure regions, generating highly destructive, extremely high pressure waves. This phenomenon which is a common cause for drop in performance and even the erosion of impeller blades is called cavitation . 10-1 Chapter 10 Introduction to Fluid Mechanics 10-9 The minimum pressure in a piping system to avoid cavitation is to be determined....
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- Spring '08