tailieunhanh - Ebook Fluid mechanics for engineers in si units: Part 2
Part 2 book “Fluid mechanics for engineers in si units” has ontents: Flow in closed conduits, turbomachines, flow in open channels, drag and lift, boundary-layer flow, compressible flow, units and conversion factors. | Chapter 7 Flow in Closed Conduits LEARNING OBJECTIVES After reading this chapter and solving a representative sample of end-of-chapter problems, you will be able to: • • • • • Understand the hydraulic classification of smooth and rough pipes. Apply the energy equation to solve practical problems related to flow in closed conduits. Calculate water hammer pressures and critical closure times for valves. Calculate flow distributions in pipe networks. Analyze and design building water supply systems. Introduction A flow in which the fluid completely fills a conduit is classified as a flow in a closed conduit. Gases generally fill the conduit in which they are being transported. In contrast to gases, liquids only undergo closed-conduit flow when there is no free surface—in other words, only when the liquid completely fills the conduit. The cross sections of closed conduits can be of any shape or size, and conduits can be made of any material. For the most part, the same general equations can be used to describe the flows of both liquids and gases in closed conduits, with the only difference being the fluid properties. In cases where the closed conduit has a circular cross section, the conduit is commonly referred to as a pipe, and in cases where the cross section is not circular, the conduit is commonly referred to as a duct, particularly when the fluid being transported is a gas. Small-diameter pipes are commonly referred to as tubes. Laminar versus turbulent flow. Flows in closed conduits can be laminar or turbulent, with each type of flow having such sufficient distinguishing features that it is worthwhile to consider them separately. The type of flow (laminar or turbulent) is usually indicated by the Reynolds number, Re, which, for pipes of circular cross section, is generally defined by VD () Re = ν where V is the average flow velocity, D is the pipe diameter, and ν is the kinematic viscosity of the fluid being transported by the .
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