Lab 8-Centrifugal Pump Experiment-Method

Fluid Mechanics Laboratory Department of Civil Engineering and Construction Engineering Management California State University, Long Beach

Lab # 8 Centrifugal pump Experiment (Prepared by Dr. Rebeka Sultana) Objectives The objective of this experiment is to determine the characteristic of a centrifugal pump. The students will operate a single pump as well as two pumps in parallel. At a fixed motor speed, the flow rates through the pumps will be varied and corresponding efficiency of the pump will be determined. The students will compute pump efficiency e fficiency at various other operating speed. General Discussion Centrifugal pumps are a radial flow rotodynamic machine. Fluid enters the rotor or impeller and thrown outwards by centrifugal action. Because of high speed of the rotation, liquid acquires a high kinetic energy and is thrown outwards by centrifugal action.

H 

P 2  P 1 

 ( z 2 

z 1 )  0

(2)

Pressure heads can be directly read in meter of H2O from the inlet and the outlet gauge of the test apparatus (see Figure 2). Equation (2) can be written as, H  (h2

 h1 )  ( z 2  z 1 )  ( h2  h1 )  H d

(3)

Datum is taken through the center of the F1-27 pump impeller and each position is given a datum head correction factor as shown in Figure 3. Following variables are used to measure pump ch aracteristics or performance, 3

Qt   / t

[m /s]

(4)

W o

[Watts]

(5)

  Qt H

 p 

Power out W o  100%   100% Power in W i

(6)

where Qt is the flow rate through the pump, W o is the power output and Wi is the power input. Wi is directly read the value from the inverter, explained in Procedure. Equipment - F1-27 Centrifugal pump test accessory. - Hydraulic bench F1-10. - A stopwatch.

Figure 2. Schematic of inlet and outlet of the pump Equipment Set up The students will operate only F1-27 pump to characterize single pump operation. 1. Inlet of the F1-27 should be connected to the sump drain valve of the F1-10. Keep the sump drain valve fully open after connecting it with the inlet of F1-27 (Figure 3). 2. Place the discharge manifold on the operating channel of the hydraulic bench. 3. Outlet of the F1-27 should be connected with the discharge manifold.

3. Outlet of the F1-27 is connected to an end of a Tee connector. One end of the Tee will be connected with the outlet of the hydraulic bench. The last outlet of the Tee connector should be connected with the discharge manifold.

Figure 4. Parallel pumps setup Procedure The experiment has two exercises. Exercise 1: Single pump operation 1. Keep the sump drain valve of the hydraulic bench open. 2. Keep the discharge control valve of the F1-27 discharge control manifold closed.

9. Repeat the steps 4-8 for pump speeds 45 Hz, 40 Hz, 35 Hz, and 30 Hz. 10. Next, set the pump speed to 50 Hz and keep the discharge control valve fully open. Now, take a set of readings by changing the settings of the sump drain valve from fully-open to fully-closed. This will show the effect of suction losses on the performance o f the pump. Exercise 2: Parallel pump operation 1. Close the control valve on the hydraulic bench and keep the sump valve open. Close the discharge control valve on the discharge control manifold. 2. Switch ON the pump in the hydraulic bench. Next, fully open the control valve in the hydraulic bench. 3. Switch ON the power on the F1-27 invertor and set the motor speed to 50 Hz. 4. Open the discharge control valve in the discharge control manifold fully and establish the flow through the system. 5. Change the settings of the discharge control value from fully open to fully closed and record inlet and outlet heads. Inlet heads of both the pump is assumed to be the same and is measured from the inlet gauge of F1-27. Outlet head can be measured from the gauge of the discharge control manifold. 6. For low flow rates (< 1.4 L/s), record the time requ ired to fill 5 L in the tanks. 7. For high flow rates 9>1.4 L/s), it is necessary to remove the sealing ball and weight from the tank and for each pump setting, allow the water level in the tank to stabilize. It may take several minutes for water to stabilize in the tank. Then read the value from the upper scale on the bench sight glass. The reading from the upper scale will be used to find the actual flow rate using the reference table, Table 1.

Table 1. Reference flow rate

Scale Reading (liters) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Flow rate (L/s) 1.41 1.44 1.48 1.51 1.54 1.57 1.60 1.63 1.66 1.69 1.72 1.75 1.78 1.81 1.84 1.86 1.89 1.92 1.94

Scale Reading (liters) 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Flow rate (L/s) 2.00 2.02 2.05 2.07 2.09 2.12 2.14 2.16 2.19 2.21 2.23 2.25 2.27 2.29 2.31 2.33 2.35 2.37 2.39

6. Calculate total head as H d  (hdo  hdi )  (ho 7. Pump power output W o

 hi ) -

H d Qv   gH d Qv  

8. Overall turbine efficiency

 p 

W o W i

 100% -

Column 11.

- Column 12. Column 13.

9. Plot a graph of measured total head Hd (along Y axis) for different flow rate Q v (along x

axis) for the same rotational speed. 10. On the same graph, plot the total head Hd for different flow rate Q v for rotational speed 45 Hz, 40 Hz, 35 Hz, and 30 Hz. 11. Plot on a separate graph, measured efficiency (along Y axis) for different flow rate Q v (along x axis) for rotational speed 50 Hz, 45 Hz, 40 Hz, 35 Hz, and 30 Hz. 12. Plot on a separate graph, measured power output (along Y axis) for different flow rate Qv (along x axis) for rotational speed 50 Hz, 45 Hz, 40 Hz, 35 Hz, and 30 Hz. 13. Plot a graph of head Hd for different flow rates Q v using the dataset for different settings of sump drain valve opening. Exercise 2 1. Motor speed (n) is measured directly in Hertz from an inverter - Column 2. 2. Find the volumetric flow rate (Qv) by collecting 5 L of water and finding the time to collect that amount of water. For low flow use the stop watch to record the time required to fill the tank – Column 5. For high flow, use the procedure explained in Exercise 2. 3. Inlet head hi and outlet head ho are read from inlet and outlet gauges, respectively – Column 6 and 8. 4. Inlet and Outlet head correction factors are 0.02 m and 0.96 m, respectively – Column 7

3. Based on power vs Flow rate graph, discuss how the pump characteristic curve changed with the rotational speed. 4. Based on the Head vs Flow, efficiency vs Flow rate, and power vs flow rate, what is the optimum operating point at each speed tested. 5. Discuss using the plot of head Hd vs Qv (the dataset for different settings of sump drain valve opening) the effect of inlet suction head on the performance of the pump. Exercise 2 1. Discuss the pump characteristic curve for two pumps in parallel setting. 2. Discuss if you get two different flow rates when two pumps were op erating in parallel. 3. Is there any difference between observed head and theoretical head? Provide reasons for any differences. References Armfield, 2011, “Centrifugal pump characteristics”, Instruction Manual.

Table 1: Single Centrifugal pump experiment Motor speed: 50 Hz No of Obs

Motor Speed n (Hz)

1 2 3 4 5 6 7 8 9 10

9|Page

Volume of water Vol (m3)

Time to collect t (sec)

Flow rate Qv 3 (m /sec)

Inlet Head hi (m of water)

Inlet head correction hdi (m)

Outlet Head ho (m of water)

Outlet head correction hdo (m)

Pump power Input Wi (Watts)

Total Head H (m of water)

Pump power output Wo (Watts)

Overall Pump Efficiency η p (%)

Motor speed: 45 Hz No of Obs

Motor Speed n (Hz)

1 2 3 4 5 6 7 8 9 10

10 | P a g e













Motor Speed n (Hz)

1 2 3 4 5 6 7 8 9 10

11 | P a g e













Motor Speed n (Hz)

1 2 3 4 5 6 7 8 9 10

12 | P a g e













Motor Speed n (Hz)

1 2 3 4 5 6 7 8 9 10

13 | P a g e












Various Sump valve settings No of Obs

Motor Speed n (Hz)

1 2 3 4 5 6 7 8 9 10

14 | P a g e












Table 2: Parallel pump configuration (pump speed 50 Hz) No of Obs

Motor Speed n (Hz)

1 2 3 4 5 6 7 8 9 10

15 | P a g e












16 | P a g e

17 | P a g e

Lab 8-Centrifugal Pump Experiment-Method

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