Experiment 9: Centrifugal Pump

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Exercise C Objective To investigate the use of the affinity laws in predicting the head-flow characteristic for a pump. Theory When selecting a pump for a system, it is seldom practical to test the performance of every size of pump in a manufacturer's range at all speeds at which it may be designed to run. It is therefore useful to have a mathematical solution that allows assumptions can be made about operating characteristics of a pump running at one speed, impeller size, etc. from experimental results taken at another. The multiple curves obtained from plotting measured pump characteristics on dimensional axes can be reduced to a single curve if appropriate dimensionless groups are used. Provided the effects of t1uid viscosity on pump performance are small, and that cavitation is not occurring, the characteristic of a given type and shape of pump may be represented by: [ ] where n is the pump speed (rpm or Hz), and D is the impeller diameter (m) For a single curve of the type suggested by this equation to represent more than one operating condition of the particular type of pump, the criterion of dynamic similarity must be fulfilled. That is, all fluid velocities at corresponding points within the machine are in the same direction and proportional to impeller speed. When this is the case, as for a particular pump operated at different speeds, a simple graph of data is formed, as depicted in Figure 4: Figure 4: Dimensionless head-discharge characteristic of a particular centrifugal pump operated at different speeds

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump The dimensionless equation given previously is the basis from which the affinity laws are derived. The affinity laws allow the performance of geometrically similar pumps of different sizes or speeds to be predicted accurately enough for practical purposes. The methods used for deriving the affinity laws will not be presented here, but the laws are as follows: ̅ Power Coefficient Flow Coefficient Head Coefficient These Laws are most often used to calculate changes in now rate, head and power of a pump when the size, rotational speed or fluid density is changed. The following formulae are derived from the above considerations, and allow calculation of total head H, and power Pm at one speed n. to be deduced from those measured at another speed n2: More generally, the relationship between two geometrically similar machines with characteristic diameters D1 and D2 operating at rotational speeds n1 and n2 is shown in Figure 5. For any two points at which values of (gH / n2D2) and (Q / nD3) are the same, it follows that: ( ) ( ) and ( ) These are termed corresponding points. The power coefficient and the resulting efficiency E can be compared in a similar manner. Figure 5: Relationship of performance characteristics for geometrically similar machines operating at different speeds

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Equipment Set Up If the results from Exercise B are available then no further data is required. Ensure you understand the Theory section then proceed directly to the results. This experiment may be undertaken directly following another experiment, in which case the equipment will already be prepared and need only be switched back out of standby mode again. If the equipment is not yet ready for use, proceed as follows: Ensure the drain valve is fully closed. If necessary, fill the reservoir to within 20cm of the top rim. Ensure the inlet valve and the gate valve are both fully open. Ensure the equipment is connected to the IFD7 and the IFD7 is connected to a suitable PC. The red and green indicator lights on the IFD7 should both be illuminated. Ensure the IFD7 is connected to an appropriate mains supply, and switch on the supply. Run the FM50-304 software. Check that 'IFD: OK' is displayed in the bottom right corner of the screen and that there are values displayed in all the sensor display boxes on the mimic diagram Procedure The results from Exercise B may be used to perform the calculations and to create the graphs for this exercise. Where these results are available, no further data is required. Proceed directly to the Results section. If results are not available, proceed as follows: Switch on the IFD7. Switch on the FM50 pump within the software. In the software, set the pump to 50%. Allow water to circulate until all air has been flushed from the system. Close the gate valve to give a flow rate Q of 0. Select the icon to record the sensor readings and pump settings on the results table of the software. Open the gate valve to give a very low flow rate. Allow sufficient time for the sensor readings to stabilise then select the icon to record the next set of data. Open the gate valve in small increments, allowing the sensor readings to stabilise then recording the sensor and pump data each time. Create a new results sheet by selecting the icon (you may also wish to save the results at this time to avoid losing the data in the event of problems). Set the pump to 70%. Close the gate valve.

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Select the icon to record the sensor readings and pump settings on the new results table. Open the gate valve to give a very low flow rate. Allow sufficient time for the sensor readings to stubilise, then select the icon to record the next set of data. Repeat, opening the gate valve in small increments and allowing the sensor readings to stabilise, then recording the sensor and pump data each time. Ensure the results are saved using 'Save' or 'Save As . .' from the software File menu after taking the final set of results. Switch off the FM50 within the software using the Power On/Standby button. Switch off the IFD7. Results The results taken at 70% will be used with the affinity laws to give predicted results at 50%. This will then be compared to the actual results at 50%. The software uses the affinity laws and to calculate the predicted values of Ht2 at predicted flow rates Q2 and 50% setting from the measured values of Htl and Q1 and the values n1 70 and n2 50. Plot a graph of Predicted Head against Predicted Flow Rate. Plot the measured Total Head at 50% against measured Flow Rate at 50% (if the data is exported into a dedicated spread sheet package or similar then it may be possible to plot both graphs on the same axes). Conclusion Compare the predicted results at 50% with the measured results. How accurate were the values obtained using the affinity laws? Discuss the advantages and disadvantages of this technique for pump system design

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Calculations Table 2: Data for 50% Setting and 70% setting from software Practical 70% 1050 rpm Sample Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 50% 750 rpm Flow Rate Q [l/s] Total Head Ht [m] Flow Rate Q [l/s] Total Head Ht [m] 0.08 0.15 0.27 0.43 0.56 0.66 0.76 0.82 0.89 0.93 1.00 1.01 1.04 1.04 1.06 1.05 1.06 1.08 1.08 1.06 3.41 3.38 3.26 3.26 3.11 2.99 2.88 2.79 2.68 2.63 2.58 2.52 2.42 2.33 2.44 2.34 2.34 2.38 2.35 2.34 0.04 0.12 0.21 0.29 0.40 0.49 0.54 0.60 0.64 0.66 0.69 0.72 0.74 0.76 0.76 0.76 0.77 0.77 0.76 1.70 1.68 1.67 1.64 1.58 1.52 1.51 1.39 1.34 1.36 1.30 1.31 1.25 1.26 1.20 1.16 1.19 1.19 1.20 Practical 4.00 Total Head Ht [m] 3.50 3.00 2.50 2.00 70% 1050 rpm 1.50 50% 750 rpm 1.00 0.50 0.00 0.00 0.50 1.00 Flow Rate Q [l/s] Figure 6 1.50

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Using Similarity Laws to calculate Q and Ht for 50% and Table 3: Data for 70% setting from software and 50% Setting from Similarity Laws Similarity Laws Calculated 50% 750 rpm 70% 1050 rpm Sample Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Flow Rate Q [l/s] Total Head Ht [m] Flow Rate Q [l/s] Total Head Ht [m] 0.08 0.15 0.27 0.43 0.56 0.66 0.76 0.82 0.89 0.93 1.00 1.01 1.04 1.04 1.06 1.05 1.06 1.08 1.08 1.06 3.41 3.38 3.26 3.26 3.11 2.99 2.88 2.79 2.68 2.63 2.58 2.52 2.42 2.33 2.44 2.34 2.34 2.38 2.35 2.34 0.06 0.10 0.19 0.30 0.40 0.47 0.54 0.59 0.64 0.66 0.71 0.72 0.74 0.74 0.76 0.75 0.76 0.77 0.77 0.76 1.74 1.72 1.66 1.66 1.59 1.53 1.47 1.42 1.37 1.34 1.32 1.29 1.23 1.19 1.24 1.19 1.19 1.22 1.20 1.19 Affinity Laws 4.00 Total Head Ht [m] 3.50 70% 1050 rpm 3.00 2.50 2.00 Calculated 50% 750 rpm 1.50 1.00 0.50 0.00 0.00 0.50 1.00 Flow Rate Q [l/s] Figure 7 1.50

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Exercise D Objective To investigate the effect of changing inlet head on pump performance. Method By varying the pressure at the inlet to the pump using a manual valve to control the available flow. Theory In both the design and operation of a rotodynamic machine, careful attention has to be paid to the fluid conditions on the suction side. In particular, it is important to check the minimum pressure that can arise at any point to ensure that cavitation does not take place. Cavitation If the pressure at any point is less than the vapour pressure of the liquid at the temperature at that point, vaporisation will occur. This is most likely to arise in the suction side where the lowest pressures are experienced. The vaporised liquid appears as bubbles within the liquid, and these subsequently collapse with such force that mechanical damage may be sustained. This condition, known as cavitation, is accompanied by a marked increase in noise and vibration in addition to the loss of head. . بالحذريج suction pipe يوكي رؤية جكىى الفماعات عي طزيك إغالق الصوام الوىجىد في FM 51 الفماعات جكىى اوضخ في الجهاس االخز : هالدظة

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Exercise E Objective To obtain a Head - Flow curve for the piping system through which the fluid is to be pumped. To determine the operating point of the pump. Theory System analysis for a pumping installation is used to select the most suitable pumping units and to define their operating points. System analysis involves calculating a head - flow curve for the pumping system (valves, pipes, fittings etc.) and using this curve in conjunction with the performance curves of the available pumps to select the most appropriate pump(s) for use within the system. The system curve is a graphic representation of the flow rate in the system with respect to system head. It represents the relationship between flow rate and hydraulic losses in a system. Such losses are due to the system design (e.g. bends and fittings, surface roughness) and operating conditions (e.g. temperature). Assuming that Flow velocity is proportional to volume now rate Losses in the system are proportional to the square of the now velocity it follows that system head loss must be proportional to the square of the volume flow rate, and the system head - now graph will therefore be parabolic in shape. بالي الشزح هىجىد في الكحالىج الخاص بالجهاس Calculations Table 4 Sample Number 1 2 3 4 5 6 7 8 9 10 11 Pump Setting S [%] 100 90 80 70 60 50 40 30 20 10 0 System Curve Pump Speed n [rpm] 1500 1350 1200 1050 900 750 600 450 300 150 0 Flow Rate Q [l/s] 1.49 1.36 1.22 1.08 0.92 0.77 0.61 0.46 0.30 0.13 0.00 Total Head Ht [m] 4.28 3.78 3.03 2.33 1.71 1.16 0.74 0.38 0.15 -0.01 -0.05

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Table 5 Pump Setting S [%] 70 70 70 70 70 70 70 70 70 70 70 70 70 70 Sample Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pump Curve Pump Speed n [rpm] 1050 1050 1050 1050 1050 1050 1050 1050 1050 1050 1050 1050 1050 1050 Flow Rate Q [l/s] 1.08 1.02 1.00 0.97 0.92 0.85 0.80 0.69 0.61 0.49 0.35 0.24 0.13 0.09 Total Head Ht [m] 2.28 2.38 2.55 2.60 2.69 2.74 2.86 2.89 3.10 3.16 3.28 3.34 3.39 3.41 Operating Point 5.00 Total Head Ht [m] 4.00 3.00 Operating Point 2.00 Pump Curve System Curve 1.00 0.00 -1.00 0.00 0.50 1.00 1.50 2.00 Flow Rate Q [l/s] Figure 8 ًمطة الحشغيل في الزسوة كاًث اخز ًمطة في : هالدظة pump curve ألى لزاءات ،system curve جن اخذها عٌذ أعلى flow( outlet valve fully opened

Hydraulics Lab - ECIV 3122 Experiment (9): Centrifugal Pump Experiment 9: Centrifugal Pump Introduction: Pumps fall into two main categories: positive displacement pumps and rotodynamic pumps. In a positive displacement pump, a fixed volume of fluid is forced from one chamber into another. One of the oldest and most familiar designs is the .