Part A – Centrifugal Pump



Lab 7: PumpsGroup Number: _______ Section Number: _______ TA Initials: _______ Name ___________________________________Other team members ___________________________________________________________________SAFETY: We’ll be using water and electricity today. The water, if spilled, can create a slip hazard and an electrical shock hazard. Carefully direct the outlet from the pump to keep all water inside the bin. Use the switch provided to turn off the pump when you are not actively collecting data.If water does spill on the table or floor, clean it up promptly with mop and/or paper towels. Only plug/unplug the pump and electrical meter after you dry your hands and clean up any spilled water.Water should not be used as a toy and splashed or squirted at anybody. Lab coats and safety glasses are required.Background: Pumps are an integral part of continuous processes used in chemical engineering. They impart mechanical energy to a fluid in a pipe, causing the pressure to increase. This counteracts the effect of friction and allows fluid to move through a system. As discussed in class, pumps do not work perfectly in transferring energy to the fluid. In this lab you will analyze the efficiency of a centrifugal pump to convert electrical energy into pressure energy. You will also analyze the accuracy of a peristaltic pump in metering flow.Part A – Centrifugal PumpProject, Part A: We’ll be using experimental data to develop a pump curve and calculate pump efficiency for a small centrifugal pump used for aquariums. You will measure the flow rate through the pump for multiple output heights (the outlet height is also called a “pressure head.” It will change how hard the pump needs to work.) and use this to generate a “pump curve.” You will furthermore calculate pump efficiencies with the help of an electrical power meter. Equipment, Part AA plastic bin to contain all the water used in the experiment.A small aquarium centrifugal pump. The pump must be operated while submerged in 3-4 cm deep water. If the water is not deep enough you will see bubbles coming through the tube. The pump has suction cups to attach to the bottom of the plastic bin. Make sure the selector switch on the pump flow inlet is moved all the way to the left at all times. Otherwise the inlet flow will be restricted.An electrical switch. Plug the pump into this and then plug this into the outlet. Turn off the switch whenever you are not actively collecting data.An electrical power meter (shared by 2 teams). Take turns using the power meter. When the pump switch is plugged into the meter, you can measure (in watts) the electrical power being used by the pump. Select the mode that reads “W” for watts and below says “cost”. If you select the correct mode, the screen should NOT say “Lo” or “Hi”.3 feet of vinyl tubing. One end has a smaller piece of tubing inserted and this should be likewise inserted into the pump outlet. The other end of the tubing has an elbow to allow convenient filling of a container.A meter stick to measure the height at which water is discharged from the tubing. Important note: To get pressure head, measure the difference in height between the outlet flow and the top of the water in the bin. “Height of outlet flow” is the point where the water leaving the tube elbow first contacts the atmosphere—this will be a slightly different height depending on whether flow is exiting vigorously or is dribbling out of the elbow.A plastic container for measuring volume and/or mass of fluid.Mass balances (shared). Note that they can only measure up to 300 grams.Procedure, Part A: Carefully read the above description of how to use the equipment and supplies so that you avoid mistakes. Make a plan for doing the following:Take multiple measurements of flow rate over a full range of pressure head values. You want to map out the entire pump curve as discussed in class. See table on next page.At some point, use the power meter to measure the wattage of your pump at each height (this can be done more quickly than the flow measurements in step 1).Use Excel to make a graph of (a) Flow rate (mL/s) vs. Pressure (kPa) and (b) Flow rate (mL/s) vs. pump efficiency (%). Make your graphs professional. In each case fit a reasonable curve to your data, which you can use to answer the discussion questions below. Turn in your spreadsheet and graphs as a part of this lab.Data, Part A: Record your measurements in columns 1, 2, 3, and 5 below. You may use the Excel spreadsheet to do repeated calculations for columns 4, 6, and 7, though you should do one set of calculations by hand to ensure proper units conversions.Time (s)Flow rate ? (mL/s)Pump Head Δh (cm)Pump ?P (kPa)? to pump (W)? to fluid(W)Efficiency %Calculation for column 4 (Pump ?P (kPa)):Calculation for ? to fluid (W): Calculation for column 7 (Efficiency %):Discussion Questions (use your excel graph and a 2nd order polynomial trendline to answer the following):You desire to install a small waterfall in your apartment for aesthetics. According to your graphs, how high could the waterfall be and still maintain a trickle if you were to use this pump? What if you wanted a 20 mL/s flow?What is the maximum gauge pressure provided by your pump? (Also using your graphs)At what flowrate does the pump have optimal efficiency? (Still using those graphs)Bonus activity, Part A: (This is optional and doesn’t count for points. The understanding you gain could be useful, however.) Using your fingernails, carefully pry off the cover over the pump inlet. Then remove the cover over the impeller. Look at what the impeller and inside of the housing look like. Based on the physics of how the impeller moves fluid through the system, can you explain the shape of the pump curve and the efficiency curve you obtained? How could the impeller/housing geometry be modified to increase the pump efficiency?Part B – Peristaltic Pump34899605080Project, Part B. You will learn to use a peristaltic pump and will calibrate it. Peristaltic pumps have the advantage that they meter the flow at the same time they are pumping it. They are useful for pumping precise but small amounts of liquids. In fact, the peristaltic pumps used in our lab were originally used in a hospital to control flow for an IV, providing a fixed flow of medicine and fluid into a patient’s bloodstream. Because they were purchased used on eBay, we need to know if they work and are properly calibrated so they can be used for later labs in this class.Equipment, Part B.Input and output water containers (can reuse bin from Part A as input container)A peristaltic pumpA set of medical (IV) tubing that is specific to the pumpA syringe and short attachment tube – used to prime the pumpRoom temperature waterGraduated cylinders and mass balances (shared by class)Thermometer (shared by the class) – The TAs will tell you the ambient temperature so you can find the right water density from the attached chart3533140427990Drip Tank00Drip TankProcedure, Part B. “Prime the pump” by getting the tubing system filled with waterAfter plugging in the pump, insert the drip tank and black rubber washer into the pump. DO NOT wrap the stretchy silicone section of the tubing around the black rollers, as shown in the picture to the right.Place the tiered purple cone (output) into an empty water container.Fill syringe and short attachment tube completely with water. Connect them to the T-shaped purple input. Push water through the whole line until bubbles are gone and water exits the purple cone.In the above step, make sure the drip tank does not fill above the horizontal line. The pump optically monitors the drip tank to make sure that liquid is properly flowing for medical purposes. If the drip tank overfills, you can make the level go down by pushing an air bubble through the line using the syringe.Once the input and output lines are full of water, stretch the silicone tube around the black rollers. Remove the syringe and short attachment tube from the input line.Start the flow experimentPlace the T-shaped purple input into a full container of liquid.Make sure the roller clamp (part of the inlet side of the tubing set that can be used to interrupt the flow) is in the fully “on” position.Turn the pump on and using either the side dial or arrow buttons set pump to desired volumetric flow rate. Then press start.Calibrate the pumpTake an empty container and weigh it before using it.Set the flow rate of the pump to 300 mL/hr.Use the pump to fill the container over the course of 10 minutes or so. Record the elapsed time and measure the volume and mass of fluid put into the container. Data, Part BPump ID number (on back of pump): ____________________Mass of Empty container: ______________ Mass of filled container: ______________Mass of water in container: _______________ Measured Volume of water in container: ___________ Calculation 1: Using the measured mass and volume of water in your outlet container, calculate the observed density of water. Density changes with temperature. Compare this density to the corresponding density on the attached chart based on the water temperature (the TAs will give the ambient temperature).Calculation 2: Calculate the actual volumetric flowrate using the previous measurements of water actually pumped through the system during the 10 minutes (or whatever time you used). Compare this to the nominal flow rate you set on the pump. How well-calibrated is the pump’s metering system (represent calibration as a percent)?Water Density as a function of temperature.Make sure to “carry the nines” down from the first density entry. _________________________________________________________________________________Grading Rubric (to be completed by TAs)PointsMaxPart A measurements reasonable2Part A calculations and analysis, including attached Excel plots with fitting curves 10Part B measurements reasonable2Part B calculations and analysis4Safety and cleanliness: TA Initial:_______2Total20 ................
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