CHE3040 Operations Laboratory Assignment

Added on - 18 Oct 2019

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abpppWnBHP2CHE 3040UNIT OPERATIONS LABORATORY ICentrifugal Pump CharacteristicsPurposeThe purpose of this experiment is to determine the effect of flow rate and speed on thehead, efficiency, and brake horsepower requirement of a centrifugal pump.Background/TheoryMcCabe, Smith, and Harriott, 5thedition1(Eqn. 8.1, p. 190), gives the following modifiedBernoulli equation (Equation 1) for systems with a pump:(1)Figure 1 illustrates the terms in this equation. For a system with no elevation changeacross the pump, Za= Zb. If the pipe diameter is the same for the suction and dischargelines, Va= Vb. Canceling the elevation and kinetic energy terms yields Equation 2:(2)where:pa= pump suction pressure [lbf/ft2]pb= pump discharge pressure [lbf/ft2]= density of fluid [lbm/ft3](Figure 2 shows water density versus temperature)Wp= ideal pump work per unit mass flowrate [lbf-ft/lbm]= overall mechanical efficiency of the pumpMultiplying the right hand side of Equation 2 by gc/g gives the head (hp)for this pumpinfeet. The shaft work or brake horsepower (BHP) for the pump can be calculated from theshaft torque and rpm readings using Equation 3.(3)where:= shaft torque [lbf-ft]n= shaft speed [min-1]BHP= shaft work [lbf-ft/min]Multiply BHP by 3.0303 x 10-5to get shaft work in horsepower [hp]. Divide BHP by themass flowrate [lbm/min] to get Wp. Once Wpis known, Equation 2 can be used to solvefor the pump efficiency.McCabe, Smith, and Harriott, 5thedition1(Eqn. 8.7, p. 191), gives the following equation(Equation 4) for available net positive suction head (NPSH) in feet:Page1of5as of August 4, 2016cbbcbbpcaacaagVggZpWgVggZp2222
Figure 1. An illustration of the terms in Equations 1, 2, and 4 (Figure 8.5, p. 190,McCabeet al1).Figure 2. Density of water versus temperaturePage2of5as of August 4, 2016
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