South valley university Faculty of Engineering 3nd Department of mechanical engineering Centrifugal pump Experiment Table of Contents 1- Introduction..................................................................................................................................... 2 2-The objective of the experiment ......................................................................................................... 3 3- Experimental Apparatus.................................................................................................................... 3 4-Measuring and instruments................................................................................................................ 5 turbine flowmeter ............................................................................................................................... 5 Bourdon tube ..................................................................................................................................... 6 5- Test Procedure ................................................................................................................................. 7 6-Results and Discussion...................................................................................................................... 7 1|Page 1- Introduction Pumps fall into two main categories: positive displacement pumps and rot dynamic pumps. In a positive displacement pump, a fixed volume of fluid is forced from one chamber into another. The centrifugal pump is, by contrast, a rotodynamic machine. Rotodynamic (or simply dynamic) pumps impart momentum to a fluid, which then causes the fluid to move into the delivery chamber or outlet. Turbines and centrifugal pumps all fall into this category. Centrifugal pumps are widely used in industrial and domestic situations. Due to the characteristics of this type of pump, the most suitable applications are those where the process liquid is free of debris, where a relatively small head change is required, and where a single operating capacity or a narrow range of capacities is required. The general design is usually simple with few mechanical parts to fail, however, and it is possible to operate a centrifugal pump outside ideal parameters while maintaining good reliability. The centrifugal pump converts energy supplied from a motor or turbine, first into kinetic energy and then into potential energy. The motor driving the impeller imparts angular velocity to the impeller. The impeller vanes then transfer this kinetic energy to the fluid passing into the center of the impeller by spinning the fluid, which travels outwards along the vanes to the impeller casing at increasing flow rate. This kinetic energy is then converted into potential energy (in the form of an increase in head) by the impeller casing (a volute or a circular casing fitted with diffuser vanes) which provides a resistance to the flow created by the impeller, and hence decelerates the fluid. The fluid decelerates again in the outlet pipe. As the mass flow rate remains constant, this decrease in velocity produces a corresponding increase in pressure as described by Bernoulli’s equation. 2|Page 2-The objective of the experiment Aims of the experiment are: 1- Comprehend the basic laws used in the centrifugal pump experiment. 2- Identify the main components of a centrifugal pump. 3- studying a centrifugal pump and recording a typical pump characteristic curve. 4- determining the pump efficiency. 5- studying how speed affects flow rate and head. 3- Experimental Apparatus 1- investigation of a centrifugal pump 2 - drive with variable speed via frequency converter 3- ball valve to adjust the head 4- manometers on the inlet and outlet side of the pump 5- digital display of speed and power 6- flow rate determined by base module HM 150 7- water supply using base module HM 150 The parts 1. display and controls 2. centrifugal pump 3. motor 4. ball valve for adjusting the head 5. outlet side manometer 6. inlet side manometer 3|Page 4|Page 4-Measuring and instruments turbine flowmeter A turbine flowmeter consists of a multi-bladed wheel mounted in a pipe along an axis parallel to the direction of fluid flow in the pipe, as shown in Figure 16.9. The flow of fluid past the wheel causes it to rotate at a rate that is proportional to the volume flow rate of the fluid. This rate of rotation has traditionally been measured by constructing the flowmeter such that it behaves as a variable reluctance tach generator. This is achieved by fabricating the turbine blades from a ferromagnetic material and placing a permanent magnet and coil inside the meter housing. A voltage pulse is induced in the coil as each blade on the turbine wheel moves past it, and if these pulses are measured by a pulse counter, the pulse frequency and hence flow rate can be deduced. In recent instruments, fiber optics are also now sometimes used to count the rotations by detecting reflections off the tip of the turbine blades 5|Page Bourdon tube The Bourdon tube is an elastic element type of pressure transducer. It is relatively cheap and is commonly used for measuring the gauge pressure of both gaseous and liquid fluids. It consists of a specially shaped piece of oval-section, flexible, metal tube that is fixed at one end and free to move at the other end. When pressure is applied at the open, fixed end of the tube, the oval cross-section becomes more circular. In consequence, there is a displacement of the free end of the tube. This displacement is measured by some form of displacement transducer, which is commonly a potentiometer or LVDT. Capacitive and optical sensors are also sometimes used to measure the displacement. A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common 6|Page 5- Test Procedure 1. Switch on the interface device, then switch on the pump within the software using the pump on/standby button. 2. Using the software, set the speed to 80%. The interface will increase the pump speed until it reaches the required setting. Allow water to circulate until all air has been flushed from the system. Slightly closing and opening the inlet valve and gate valve a few times will help in priming the system and eliminating any bubbles caught within the valve mechanism. Leave the inlet valve fully open. 3. In the results table, rename the spreadsheet (Select Format> Rename Sheet) to 80%. 4. Close the gate valve to give a flow rate Q of 0. (Note that the pump will not run well with the gate valve closed or nearly closed, as the back pressure produced is outside normal operating parameters. The pump should begin to run more smoothly as the experiment progresses). 5. Select the (Go) icon to record the sensor readings and pump settings on the results table of the software. 6. Open the gate valve to allow a low flow rate. Allow sufficient time for the sensor readings to stabilise then select the (Go) icon to record the next set of data. 7. Increase the flow in small increments, allowing the sensor readings to stabilise then recording the sensor and pump data each time. 8. Using the arrow buttons on the software display, reduce the pump speed to 0%. Select "Save" or "'Save as..." from the "file" menu and save the results with a suitable file name. 9. Switch off the pump within the software using the power on standby button, then switch off 6-Results and Discussion Sample calculation: πππ π = 1439 πππ 2ππ π= 60 7|Page 2π(1439) 60 π = 150.69 πππ⁄π −1 π= πππππ’π = 1.1 ππ ππππ’π‘ πππ€ππ = ππ = ( 150.69 πππ⁄π −1 )( 1.1 ππ ) = 165.76 πππ‘π‘ πΆππππππ‘π¦ , π π = 90 πΏ⁄πππ = 90 πΏ⁄πππ⁄( 1000πΏ )( 60π ) = 1.5 × 10−3 π3 ⁄π 1 ππ = ( 41.36 + .98 )πππ⁄( 1000 πππ−3 )(9.81ππ −1 ) = 4.32 π π€ππ‘ππ βπππ, β = ( π2 − π1 ) ππ’π‘ππ’π‘ πππ€ππ = πππβ = (1000 πππ−3 )(9.81 ππ −2 )(1.5 × 10−3 π3 ⁄π )(4.32π) = 63.52 πππ‘π‘ πΈπππππππππ¦ , Ζ = ππ’π‘ππ’π‘ πππ€ππ ππππ’π‘ πππ€ππ 8|Page = πππβ ππ = (63.52 πππ‘π‘ )⁄(165.76πππ‘π‘) = 0.383 × 100% = 38.3% Test 1 Pump Speed, N: 1439 rpm ω: 150.69 rad/s Test 2 9|Page Pump speed, N: 2178 rpm ω: 228.08 rad/s Test 3 Pump speed, N: 2945 rpm ω: 308.4 rad/s 10 | P a g e Pump Performance Curves (N=1439rpm, ω= 150.69 rad/s): 11 | P a g e Pump Performance Curves (N=2178 rpm, ω= 228.08 rad/s): Pump Performance Curves (N=2945 rpm, ω= 308.4 rad/s): 12 | P a g e 13 | P a g e
