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Unformatted text preview: I N T E R N A L F L O W F luid flow is classified as external or internal , depending on whether the fluid is forced to flow over a surface or in a conduit. Internal and exter-nal flows exhibit very different characteristics. In this chapter we con-sider internal flow where the conduit is completely filled with the fluid, and flow is driven primarily by a pressure difference. This should not be con-fused with open-channel flow (Chap. 11) where the conduit is partially filled by the fluid and thus the flow is partially bounded by solid surfaces, as in an irrigation ditch, and flow is driven by gravity alone. We start this chapter with a general physical description of internal flow through pipes and ducts including the entrance region and the fully devel-oped region. We continue with a discussion of the dimensionless Reynolds number and its physical significance. We then introduce the pressure drop correlations associated with pipe flow for both laminar and turbulent flows. Then we discuss minor losses and determine the pressure drop and pumping power requirements for real-world piping systems. Finally, we present a brief overview of flow measurement devices. 245 CHAPTER 8 OBJECTIVES When you finish reading this chapter, you should be able to n Have a deeper understanding of laminar and turbulent flow in pipes and the analysis of fully developed flow n Calculate the major and minor losses associated with pipe flow in piping networks and determine the pumping power requirements n Understand various velocity and flow rate measurement techniques and learn their advantages and disadvantages Internal flows through pipes, elbows, tees, valves, etc., as in this oil refinery, are found in nearly every industry. 8–1 n INTRODUCTION Liquid or gas flow through pipes or ducts is commonly used in heating and cooling applications and fluid distribution networks. The fluid in such appli-cations is usually forced to flow by a fan or pump through a flow section. We pay particular attention to friction , which is directly related to the pres-sure drop and head loss during flow through pipes and ducts. The pressure drop is then used to determine the pumping power requirement. A typical piping system involves pipes of different diameters connected to each other by various fittings or elbows to route the fluid, valves to control the flow rate, and pumps to pressurize the fluid. The terms pipe , duct , and conduit are usually used interchangeably for flow sections. In general, flow sections of circular cross section are referred to as pipes (especially when the fluid is a liquid), and flow sections of non-circular cross section as ducts (especially when the fluid is a gas). Small-diameter pipes are usually referred to as tubes . Given this uncertainty, we will use more descriptive phrases (such as a circular pipe or a rectangular duct ) whenever necessary to avoid any misunderstandings....
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This note was uploaded on 10/16/2010 for the course GEEN 3311 taught by Professor Dr.ra’fatal-waked during the Fall '10 term at Prince Mohammad Bin Fahd University, Dhahran.
- Fall '10