Grand Valley State University The Padnos School of Engineering WATERBED PUMP EGR 365 FLUID MECHANICS Brad Vander Veen May 27 2003 Lab Partners Julie Watjer Thomas Freundl PURPOSE The purpose of this lab is to measure the suction developed by a simple venturi pump as a function of the flowrate through it and to compare those measurements with the predictions from Bernoulli s equation THEORY Consider the diagram of the waterbed pump below in Figure 1 Figure 1 Diagram of Waterbed Pump Writing Bernoulli s equation from 1 to 2 yields p1 1 2 p 1 2 v1 gz1 2 v 2 gz 2 w 2 w 2 where p is the pressure w is the density of water v is the velocity g is acceleration due to gravity and z is the depth 1 It is also known that v Q A 2 where Q is the volumetric flowrate and A is the cross sectional area Neglecting the effects of gravity on the system the following equations can be derived from equations 1 and 2 4 1 2 d2 p 2 p1 w v 2 1 2 d1 3 d 4 2 1 d1 4 z man 1 Q 2 2 g A2 2 where z is the height difference on the manometer It is known that p 2 atm w 1 94 slugs ft 3 d 1 0150 ft d 2 0375 ft Applying these values to Equation 3 yields suction pressure as a function of volumetric flowrate Q Q suction pressure Q 0 5 w A 2 2 d 4 2 d 1 1 1 144 where suction pressure is in psi This theoretical function for suction pressure can be plotted as seen below in Figure 2 Suction Pressure vs Flowrate 20 suction pressure Q 10 psi 0 0 0 005 Q ft 3 sec Figure 2 Theoretical Plot of Suction Pressure APPARATUS ITEM Waterbed Pump Manometer Flowmeter Garden Hose Trap 5 PROCEDURE 1 Assemble the experimental setup as seen in Figure 1 2 Using various flowrates record the height difference from the manometer RESULTS Table 3 below shows the manometer reading at different flowrates through the pump Flowrate cfs Height feet 0 00474 2 625 0 00521 2 792 0 00568 3 625 Table 3 Manometer Readings Using these manometer readings the experimental suction pressure can be found using the formula pressure g z 6 In Table 4 below the experimental suction pressure is shown Flowrate cfs Height feet Suction Pressure psi 0 00474 2 625 1 139 0 00521 2 792 1 211 0 00568 3 625 1 573 Table 4 Experimental Suction Pressure ANALYSIS The results from the theoretical and experimental resutls can be compared as seen below in Table 5 Flowrate cfs Theoretical S P psi Experimental S P psi discrepency 0 00474 4 722 1 139 76 0 00521 5 705 1 211 79 0 00568 6 781 1 573 77 Table 5 Comparison of Theoretical and Experimental Values The theoretical values and experimental values can also be compared on the same plot as seen below in Figure 6 10 suction pressure Q s p 5 psi 0 0 004 0 006 Q q ft 3 sec Figure 6 Plot of Theoretical and Experimental Values The theoretical and experimental values follow the same trend however they disagree with a relatively large percent discrepancy This discrepancy could be contributed mostly to the fact that the pump is not perfect and experiences significant losses during operation Since our theoretical model does not compensate for the losses there will be quite a large discrepancy between the two CONCLUSION In this lab the operation of a small venturi pump was analyzed A theoretical model was created using Bernoulli s equation and experimental data was also taken and compared to the theoretical model The theoretical and experimental data followed the same trend but did not agree numerically due to significant losses during pump operation