Determine the Effect of Flow Rate | Experiment
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Added on 2019-09-30
Determine the Effect of Flow Rate | Experiment
Added on 2019-09-30
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Date: October 8, 2015Lab Report: Centrifugal Pump CharacteristicsSummary:The purpose of this experiment was to determine the effect of flow rate, speed of water at thehead, efficiency and the brake horsepower requirement of a centrifugal pump. Three separate experimentswere conducted at different speeds; 1000 rpm, 1250 rpm, 1500 rpm, and 1750 rpm with different flowrates of 0, 2, 4, 8, 12 and 16 gallons per minute (gpm). Further calculations were made by utilizingnumerous equations in order to obtain values of the pump head (hp), shaft work (BHP), net positivesection head (NPSH) and efficiency. Furthermore, I have analyzed the relationship of the brakehorsepower, pump head, and efficiency versus the volumetric flowrate. It was concluded that the brakehorsepower at different pump speeds increase as the flow rate increases, the pump head decrease as thevolumetric flow rate increases, and the efficiency increases as the flow rate increases. Surprisingly, thenet positive suction head at speed 1750 rpm drops rapidly with increasing flow rate. Furthermore, finalresults exhibit that the shaft work increases gradually as the flow rate increases. Background and Methods:Pump System Description:The main objective of this experiment was to determine the impact of flow rate and speed on the head, efficiency and brake horsepower requirement of a centrifugal pump. The centrifugal pump as seen in figure 11 was used for this experiment. The pump receives water from the tank, labeled as 9 in Figure11, which is connected to the suction line going into the pump. The discharge line consists of a valve to allow for user variance of the volumetric flow rate. Then, the water is returned to the tank. In order to measure the suction and discharge pressures, two gauges connected to respective lines are used. Additionally, Torque reading is obtained from the torque gauge that is fitted on the pump.Pump Equipment:The system in figure 1 consist of: 1A- Suction Pressure gauge, P1 [in.H2O gauge].1B- Discharge Pressure gauge, P2 [psig].2A- Inlet (Suction) line.2B- Outlet (Discharge) line.3- Shaft Torque meter ().4- Flow rate meter.5-Rheostat for pump speed control. 6- Stroboscope to set pump rpm.7-Pump Impeller8-Pump Motor.
Figure 11. The pump system that has been used for the experiment.Measurement Procedure:The centrifugal pump was run at four speeds; 1000, 1250, 1500 and 1750 revolution perminute (rpm). The motor rheostat, labeled as 5 in Figure 21, was used to adjust these readingsand made accurate by using the stroboscope (6). At each different speed, measurements of thesuction pressure using gauge 1A from Figure 11, discharge pressure from gauge 1B and thetorque from Figure 11 were measured. Those measurements were taken at flow rates of 0, 2, 4, 8,12 and 16 gallons per minute. After that, the motor was stopped slowly by decreasing therheostat to zero. Finally, the pump was operated in reverse rotation at different speeds, and theflow rate with discharge valve wide open was observed.Centrifugal Pump Calculation:
Pump Head:The pump head (hp), McCabe, Smith, and Harriott, 5th edition 2 gives Equation 1 to be applied. hp=Pb−PaρEquation.1Where:Pa= pump suction pressure [lbf/ft2]Pb = pump discharge pressure [lbf/ft2] = Density of fluid [lbm/ft3]According to McCabe, Smith, and Harriott, 5th edition 2, the shaft work or horsepower for the pump can be calculated from the shaft torque and rpm readings in Equation.2: BHP=2πτnEquation.2Where:τ = shaft torque [lbf-ft]n = shaft speed [min-1]BHP= shaft work [lbf-ft/min]Based on McCabe, Smith, and Harriott, 5th edition 2, the ideal pump work per unit mass flow rate [Ibf . ft/Ibm} can be calculated from Equation.3: Wp= BHP∈hpmassFlowRate∈lbm/minEquation.3McCabe, Smith, and Harriott, 5th edition 2 gave Equation.4, where NPSH can be calculated in feet: NPSH¿gcg(pa'−pvρ−hfs)−Za Equation.4Where,Pa’ = absolute pressure at surface of reservoir [lbf/ft2]Pv = vapor pressure of fluid [lbf/ft2]hfs = friction loss in suction line [lbf- ft/lbm]Za = height of pump above surface of suction reservoirgc = gravitational proportionality constant = 32ft-lbf/s2 - lbfg = gravitational acceleration constant = 32.174 ft/s2Which will make the, (gcg=1 lbm/ lbf).
Result and Discussion:As shown below in Table 1 to 4 Pa values in H2O were recorded at different volumetric flow rate at 4different speed and the mean values, standard deviation and 95% confidence interval values are shown.Table 1: Pa (in H2O) data collected over three weeks at 1000 RPM with mean, standard deviation and 95% confidence intervalvalues1000 RPM (Pa)(in H2O)volumetricFlowrate (GPM)Week#1Week#2Week #3MeanSTDCon.95%interval05.66.04.35.30.91.025.66.04.35.30.91.045.66.04.35.30.91.085.65.54.05.00.91.0124.04.83.03.90.91.0161.00.00.00.30.60.7Table 2: Pa (in H2O) data collected over three weeks at 1250 RPM with mean, standard deviation and 95% confidence interval values.1250 RPM (Pa)(in H2O)volumetricFlowrate (GPM)Week#1Week#2Week #3MeanSTDCon.95%interval05.65.64.85.30.50.526.05.64.75.40.70.845.85.54.55.30.70.885.85.24.05.00.91.0123.53.93.03.50.50.5161.00.00.00.30.60.7Table 3: Pa (in H2O) data collected over three weeks at 1500 RPM with mean, standard deviation and 95% confidence intervalvalues.1500 RPM (Pa)(in H2O)volumetricFlowrate (GPM)Week#1Week#2Week #3MeanSTDCon.95%interval06.56.15.05.90.80.926.05.74.85.50.60.746.05.54.75.40.70.785.75.24.05.00.91.0124.03.53.03.50.50.6160.90.00.00.30.50.6Table 4: Pa (in H2O) data collected over three weeks at 1750 RPM with mean, standard deviation and 95% confidence interval values.
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