To: Mitch Cottrell, Instructor From: Brian Garber, Crawford Binns, Jeff Hollis (Group 3, Sec. J) Subject: Project Deliverable #3 Date: 4 May 2010

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1 To: Mitch Cottrell, Instructor From: Brian Garber, Crawford Binns, Jeff Hollis (Group 3, Sec. J) Subject: Project Deliverable #3 Date: 4 May 2010 This projects intention is to investigate how adjusting certain parameters of a Venturi jet affect its performance. As the typical purpose of these devices is to induce a vacuum with a liquid to entrap a secondary material, we decided to use a pressure transducer. The only must for the transducer was that it read both positive and negative pressures as we were unsure of the performance of our fabricated system. The initial decision for our transducer was to be a differential pressure, diaphragm unit from Omega.com (PX BD5V). This sensor offered several features that made it a good choice. The option for a differential reading would have given us the option to read the pressure at different locations along the venturi and the transducer could have also been piped to read the gauge pressure of the vacuum, or measuring its difference to the ambient pressure. It was also cheap (relatively). After discussing the project though, it was decided to use an already available pressure transducer. A SUNX DP-Y27 was used in the end. This sensor s range was ±100kPa, which was more than five times the range the Omega.com transducer, and turned out to be quite necessary as our device saw higher positive that we had anticipated. The SUNX also provided a digital display built into the sensor that proved quite helpful. Another feature was the ability to withstand water. The Omega would have required remote mounting using rubber hosing, and certainly greater chances for leaks in the vacuum. With the ability of the Ramco to read water pressure without faulting, the sensor could be safely mounted directly onto the system without fear. The actual Venturi was constructed out of PVC and either cemented together or utilized high viscosity grease to seal press fittings. Consistent pressures were ensured by mounting the orifice vertically, thus keeping standing water from affecting readings. The two independent variables were the size of the nozzle and the total water flow through the nozzle. The nozzle was simply created by drilling a hole in a dead end PVC cap and increasing its diameter for each test series. The flow was determined using the flow gauge built into the pump station located in room 317. The major problem that we encountered was not being able to get the SUNX to output the analog voltage signal. After spending several hours studying the wiring diagrams and trying many different configurations, the 1V-5V signal was never found. The fault is not believed to lie with the DAQ board or the lab view program. The program is an adaptation of the same program used for the class s thermocouple homework assignment. The major changes being the alteration of the signal sampling rate, which was changed in hopes of alleviating any pulsing effects from the pump, and the inclusion of the correct equation for converting the voltage input into to pressure (Psig) output. Otherwise the program followed the same format as that of the Thermocouple homework. It created a virtual channel for the analog voltage input, which was then read by the program at a given sampling rate. This data was then combine with

2 a time to form a 2-dimensional array. Using a Butterworth filter the noise of the signal was reduced as the data got passed through numerous arithmetic blocks to convert voltage into a psi pressure. A time stamp was created and the output in psi was saved to an Excel spreadsheet (screen shots of the front panel and block diagram are located in the Appendix). This short fall did not prevent our execution of our experiment though because of the digital display located on the sensor itself. The internal circuitry displayed the pressure in Psi with a resolution of (±0.02). We did calculate the uncertainty of the readings as if the sensor had worked correctly though. There were two components that would need to be taken into account. First, the pressure transducer had four types of uncertainty, and then the USB 6009 that was used for the analog data analysis had two types of uncertainty. The nominal value of the pressure that was used in the calculation was the maximum for the transducer, psid. The transducers uncertainty calculations can be seen in (Table 1) in the attachments. These uncertainties are as follows: Pressure Resolution (Abs. Accuracy) = 0.02 psid Linearity = 0.1% F.S. = * = psid Nonrepeatability = 0.2% F.S = psid Temperature = 0.3% F.S. = psid And for the 6009: Resolution = 5/ (214-1) * 4 = psid, where the 5 represents the maximum voltage, and 4 represents the maximum used in the system Absolute Accuracy = * 4 = This produced a total uncertainty in the pressure differential of pisd through perturbation of all uncertainties, which is approximately 1% of the maximum pressure differential, but much more significant for lower pressure readings of interest. Despite this large setback, we believe that our experiment yielded honest and logical results. With our basic understanding of the fundamentals of a Venturi, we expected that an increase in vacuum would occur when the flow of the pipe increased but we were mistaken. Or at least that was not the case with our rudimentary set up. The highest vacuums were not found with either the larger flows or the larger nozzle sizes. Instead our highest recorded vacuum was from smallest hole size (0.132 ) at only two gallons per minute. The other nozzle sizes, ranging from (0.151 ) to (0.661 ) consistently had a lower vacuums (higher pressure) at a given flow rate than the nozzle size beneath them (see Table 2). This led us to the conclusion that one major consideration in the Venturi s performance is not the flow rate but rather the velocity of the water exciting the nozzle. This pattern is exemplified in Fig. 1 with the addition of altitude lines showing pressure inversely proportional to flow rate. The second pattern we noticed implied that an additional variable is key to the Venturi s performance. All of the tests ran at greater than 4.5 g/min resulted in positive pressures inside the system. This was not explained by the correlation between velocities of a higher flow and larger nozzle matching the velocity of a lower flow and smaller nozzle. The factor that we determined to be hindering the Venturi was the ratio between

3 nozzle size and pipe size. Our piping remained the same for all nozzle sizes and the steady upturn in pressure (seen in Fig. 2) means that a backpressure is being encountered downstream from the Venturi. While the couplers between joints did not prevent the lower flows from pulling a vacuum, their restriction rendered higher flows incapable of making a vacuum. While we deem this experiment a success, the sensor we used was not. Through either our fault, or a fault of the sensor, we were not able to properly utilize our LabView program or our DAQ board. From our understanding from the semesters material, we tried to eliminate any possible error that we made that would have kept the sensor from outputting properly but did not come up with any solutions besides using the attached digital display.

4 Appendix

5 Table 1 Uncertainty in Diff. Pressure Pertubation A C D F G H J K L M N Index Device Range Feature Resolution Uncert or Unc in Pdot Sig+ Sig- (uncpdot)^2 Nominal Name Res * FS Pdot Sunx DP-Y27 +/- 5V out Pres. Res. ABS Lin +/- 0.10% FS Temp +/- 0.30% FS Nonrepeat +/-.2% FS V DAQ 14 bit resolution 14 bit res V Abs Acc SUM SQRT TotUnc Pdot Table 2 Diameter in (inches) GPM

6 Pressure (Psig) Pressure (Psig) Fig: 1 Flow vs Pressure vs Nozzle Size Flow (GPM) Fig: 2 Flow vs Pressure vs Nozzle Size Flow (GPM)