Energy Losses in Bends - Updated Energy Losses in Bends...

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Updated 11/26/08 Energy Losses in Bends Introduction Energy losses in pipe flows are the result of friction between the fluid and the pipe walls and internal friction between fluid particles. Minor (secondary) head losses occur at any location in a pipe system where streamlines are not straight, such as at pipe junctions, bends, valves, contractions, expansions, and reservoir inlets and outlets. In this experiment, you will measure minor head losses through a pipe section that has several bends, transitions, and fittings as shown in Figure 1. Figure 1. Schematic drawing of the energy-loss apparatus. Objective The objectives of this lab are to measure head losses through bends, transitions, and fittings, and to use these measurements to estimate the loss coefficients for each transition or fitting. Theory The energy balance between two points in a pipe can be described by the Bernoulli equation, given by L h g V z p g V z p + + + = + + 2 2 2 2 2 2 2 1 1 1 γ , (1) where p i is static pressure (in Pa) at point i , is specific weight of the fluid (in N/m 3 ), z i is the elevation (in meters) of point i , V i is the fluid velocity (in m/s) at point i , g is the gravitational constant (in m/s 2 ), and h L is head loss (in meters). The term p i / is referred 1
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Updated 11/26/08 to as the static head; z i is the elevation head; and V i /2g is the dynamic (or velocity) head. The summation of the static head and the elevation head, p i / γ + z i , is referred to as the piezometric head. The piezometric head is what is measured with the piezometer (manometer) board on the apparatus for this experiment. Head loss, h L , includes the sum of pipe friction losses, h f , and all minor losses, = + = n 1 i i f L h h h , (3) where h i is the minor head loss (in meters) for the i th component and n is the number of components (fittings, bends, etc.). Pipe friction losses are expressed as the Darcy- Weisbach equation given by g V D L f h f 2 2 = , (2) where f is a friction factor, L is the pipe length, and D is the pipe diameter. Pipe friction losses are assumed to be negligible in this experiment. Minor losses occur at any bend, transition, or fitting where the streamlines are not straight and are proportional to the velocity head. For all components, head loss is given by g V K h i i 2 2 = , (5) where K i is the loss coefficient (dimensionless) for the i th component and V is the fluid velocity as it travels through the pipe component. For the expansion and contraction, the V used in Equation (5) is the velocity of the fluid in the smaller-diameter pipe. In this experiment, the loss coefficients for different pipe components will be
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Energy Losses in Bends - Updated Energy Losses in Bends...

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