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Unformatted text preview: Chapter 14 Flow in Pipes Piping Systems and Pump Selection 14-62C For a piping system that involves two pipes of different diameters (but of identical length, material, and roughness) connected in series , ( a ) the flow rate through both pipes is the same and ( b ) the pressure drop across smaller diameter pipe is larger. 14-63C For a piping system that involves two pipes of different diameters (but of identical length, material, and roughness) connected in parallel , ( a ) the flow rate through the larger diameter pipe is larger and ( b ) the pressure drop through both pipes is the same. 14-64C The pressure drop through both pipes is the same since the pressure at a point has a single value, and the inlet and exits of these the pipes connected in parallel coincide. 14-65C Yes, when the head loss is negligible, the required pump head is equal to the elevation difference between the free surfaces of the two reservoirs. 14-66C The pump installed in a piping system will operate at the point where the system curve and the characteristic curve intersect. This point of intersection is called the operating point . 14-67C The plot of the head loss versus the flow rate is called the system curve . The experimentally determined pump head and pump efficiency versus the flow rate curves are called characteristic curves . The pump installed in a piping system will operate at the point where the system curve and the characteristic curve intersect. This point of intersection is called the operating point . 14-31 h pump pump System demand curve Operating point Flow rate Head Chapter 14 Flow in Pipes 14-68 The pumping power input to a piping system with two parallel pipes between two reservoirs is given. The flow rates are to be determined. Assumptions 1 The flow is steady and incompressible. 2 The entrance effects are negligible, and thus the flow is fully developed. 3 The elevations of the reservoirs remain constant. 4 The minor losses and the head loss in pipes other than the parallel pipes are said to be negligible. 5 The flows through both pipes are turbulent (to be verified). Properties The density and dynamic viscosity of water at 20 C are = 998 kg/m 3 and = 1.002 10-3 kg/ m s (Table A-15). Plastic pipes are smooth, and their roughness is zero, = 0 (Fig. A-32). Analysis This problem cannot be solved directly since the velocities (or flow rates) in the pipes are not known. Therefore, we would normally use a trial-and-error approach here. However, nowadays the equation solvers such as EES are widely available, and thus below we will simply set up the equations to be solved by an equation solver. The head supplied by the pump to the fluid is determined from (1) 0.68 ) m/s 81 . 9 ( ) kg/m (998 W 7000 pump 2 3 motor- pump pump in elect, h V gh V W = = We choose points A and B at the free surfaces of the two reservoirs. Noting that the fluid at both points is open to the atmosphere (and thus P A = P B = P atm ) and that the fluid velocities at both points are zero (...
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This homework help was uploaded on 04/18/2008 for the course EML 3007 taught by Professor Chung during the Spring '08 term at University of Florida.
- Spring '08