DEPARTMENT OF MECHANICAL & AEROSPACE ENGINEERING 1 CENTRIFUGAL PUMP PERFORMANCE LABORATORY-FLUID-DYNAMICS ME203 HEAT AND FLOW 2 Department of Mechanical and Aerospace Engineering University of Strathclyde, Glasgow Introduction University of Strathclyde

Engineering Centrifugal pumps are widely used both in industrial and civil environments. Due to their high efficiency, inexpensive production methods and intrinsic reliability they are the most used pumps in the world. In order to save energy during their usage and preserve the impeller from damage (due, for instance, to cavitation) a proper understanding of the principles on which pumps are based and of their performances is of crucial importance. In this laboratory session, we will perform an experiment to determine the pump performance curves, by measuring the quantities required to plot the pump head and efficiency curves as a function of the volumetric flow rate. 2 Centrifugal pump performance rig Although a centrifugal pump is a complex system, the basic knowledge provided in the class of Heat and Flow 2 is enough to implement the required procedure. THIMIN The most convenient way to understand the experimental set-up and associated procedure is to start from the sketch (pipe flow layout) depicted in Figure 1 on the following page. As evident in this sketch, a water reservoir is connected to the centrifugal pump. The water is drawn from the reservoir to the pump through a one-way valve and a strainer. Then it passes through the pump inlet valve, and enters the pump. Before coming back to the reservoir, water meets a delivery/regulation valve and, finally, a Venturi-meter. UNIVERSITY OF STRATHCLYDE- MAE All these compo- nents are installed on a mobile frame (not shown in Figure 1), by which the entire rig can easily be displaced. In the sketch it can also be seen that the pump is driven by a variable speed electric motor. The motor-to-pump assem- bly includes a force sen- sor (load cell) to mea- sure the torque and a tachometer sensor to measure the motor an- gular velocity. Pump Inlet valve Po Electric motor -PI Centrifugal pump performacne ME203 HEAT AND FLOW 2 Delivery/regulation valve Filter/Strainers One-way valve the pressure increase produced by the pump: Water reservoir In addition to these sensors, the rig is equipped with a pres- sure tapping in the pipework and on the venturi-meter. Moreover four different mechanical gauges or digital displays are available to measure the pressure in different points of the circuit. In particular, the pressure sensor connected to venturi-meter is a differential pressure transducer and gives in output the difference of pressure Apventuri between the inlet and the throat of the venturi-meter. The other two sensors are transducers that provide the pump inlet (p₁) and outlet (po) pressures, respectively. In Figure 1 the positions of these pressure sensors are highlighted using the symbol ×. Apventuri Figure 1: Schematisation of the pump testing rig. 2 Venturi-meter 3 Aim of the experiment As explained above, this experiment aims to determine the pump performances curves. We are therefore interested in plotting the head-flow rate (H – Q) and the efficiency-flow rate (n − Q) curves. To do so we define the following relations between measured quantities: H = Po - PI (1) the meaning of PO and PI has been explained above; their difference is propor- tional to the head gained by the fluid when it passes through the pump; Using standard formulas for the venturi meter the flow rate can be determined UNIVERSITY OF STRATHCLYDE- MAE as: Q = C₁A₁ = The meaning of Apventuri has been provided above, p is the density of the water (for clean water at room temperature we can assume p 10³ kg/m³), A₁ and A₂ are the venturi-meter inlet and throat area respectively (in this case we are using a venturi-meter having A₁ = 0.58107.10-³ m² and A2 = 0.2688.10-³ m²) and the coefficient Ca is the so-called coefficient of discharge ( in this case Ca = 0.97); • the hydraulic power of the pump can be determined as: W₂ = (PO - PI)Q (3) • the power input to the pump (electric energy provided to the pump) can be expressed as: (4) 2πNT 60 where is the torque ([Nm]) and N is the pump speed ([rev/min]); efficiency will read accordingly: W₁ n = Centrifugal pump performacne ME203 HEAT AND FLOW 2 24pventuri P(A/²2 - 1) = W₂ W₁ where pressure is given in [Pa], the flow rate Q in [m³/s] and power in [W]. At this stage, it becomes evident that in order to calculate the quantities above, we need to measure: p₁ [Pa], po [Pa], Apventuri [Pa], N [rev/min] and 7 [Nm]. The eqs. (1)-(5) will work correctly only if the units of measure are those listed above (be careful when you post-process the experimental measurements). 3 (5) 4 Experiment protocol In this experiment, we will determine the pump performance curves for two different values of N. You can refer to Figure 2 on the next page to visualize the position of the instruments mentioned in the following discussion. The required steps can be summarised as follows: 1. Verify that the inlet valve and the delivery/regulation valve are fully open. 2. Switch on the Pump 1 Control Panel isolator. 3. Press the "hold and zero" button in order to have a correct measurement of the torque. 4. Start the pump motor and run it to maximum speed using the set speed controller. UNIVERSITY OF STRATHCLYDE- MAE Pump 1 Control Panel T and N display Hold and zero button Pump 1 Elettric Motor = pressures, display Set Speed OO Venturi-meter ME203 HEAT AND FLOW 2 **** Delivery/regulation valve Centrifugal pump performacne ‒‒‒‒‒‒ Pump 1 Inlet valve Water Reservoir Figure 2: Representation of the testing rig. 5. Use the bleed line to bleed all pressure gauges. 6. Adjust the motor to the speed (N) needed for the experiment. You will start setting N 3000 rev/min. 7. Record all the readings using the Table 1 on page 6. Note that all the measurements can be read on the control panel, the values of N and 7 appearing in the left screen while the values of pi, po and Apventuri the central screen. In the central screen p₁ is called p2 and po is called p4. Before recording all the needed values wait until the value of each quantity is stable (it does not vary anymore). 8. Regulate the regulation valve by closing it slightly in order to find a new operation point. Re-adjust the motor speed N needed and record the new readings. Be careful! The INLET VALVE must never be closed or regulated! 9. Repeat point 8 until you collect the data for 10 operation points. Do never fully close the regulation valve. 10. Once you have collected the data for N = 3000 rev/min, fully open the regulation valve and set N = 2700 rev/min. Repeat the procedure 7, 8 and 9. UNIVERSITY OF STRATHCLYDE- MAE Note that the load cell to measure the torque is very sensitive. Do no touch it while you are carrying out the experiment, otherwise you will get results that make no sense. 5 ME203-HEAT AND FLOW 2 Post-processing of the data After collecting all the data, post-process them to plot the H - Q and n - Q curves. To do so, You may create a spreadsheet, for example using EXCELⓇ or MATLABⓇ, where you can implement eqs. (1), (2), (3), (4) and (5). Note that the pressures are displayed in [bar] but, in order to have the correct result they need to be converted in [Pa]. Once you have calculated Q, H and n you can plot the data and fit them using a built-in function¹. You may also use a pocket calculator to compute the required quantities and draw hand the required curves. 6 Final output After the post-processing procedure, you are expected to: • Plot in the same figure the H - Q curves for two values of N. • Plot in the same figure the n Q curves for two values of N. Briefly discuss the graphical results underlining the influence of N on the two curves (H-Q and n − Q curves). ¹For this task, plenty of different functions exist. You can, for instance, use the Scatter with Smooth Lines and Markers function of EXCEL® or the plot function with markers of MATLABⓇ. Refer to the software's guide for more information about the image plotting. If you want to obtain better graphical results you can use some interpolation functions as well. Centrifugal pump performacne