Hydro Turbine Project Final Report

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Turbomachinery report detailing a Hydro Turbine project from my Turbomachinery class at Cal Poly.

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Hydro Turbine Project Final Report

  1. 1. Hydraulic Turbine Design Project ME 443 Spring 2008 Caleb Bartels William Burgess June 5, 2008 California Polytechnic State University- San Luis Obispo Mechanical Engineering Department
  2. 2. !"#$%&'($) The objective for the Hydraulic Turbine project was to create a turbine, powered solely by a water reservoir, to pull a one pound can of Garbanzo beans ten feet in the shortest possible time. The turbine was limited to one gallon of water emitted from the water reservoir over the course of each run. The water reservoir height could be no higher than 4 feet 3 inches, capping the maximum total head of the system. The water reservoir also required a mechanism to start and stop the water flow to the turbine. *$+',-)./-+'0$12&'/-+) Our team brainstormed possible solutions to the design challenges listed. We discussed the tradeoffs between Crossflow turbines and Pelton turbines, taking into account ease of manufacturing, performance, and cost. Crossflow turbines were readily available for purchase while a Pelton wheel could be manufactured using the rapid prototyping machine in the Mechanical Engineering Department. Our team desired a self designed turbine that was efficient, leading to the selection of a Pelton turbine. A Solidworks drawing of our final turbine assembly can be seen below. Figure 1. Final CAD rendering of the turbine assembly. We recognized that the system piping and nozzle design would require more time than the construction of the reservoir housing. The reservoir support was to be simple and non-intensive in labor. Overall, our team recognized the importance of adjustability in design. While we planned to calculate the system as well as we could, translating that
  3. 3. into a precise actual design can be difficult and adjustments would be needed to maximize performance. We valued testing to determine the full performance of our system. 3$4&/-)56%7$&)*$+',-) The design of the Pelton buckets was performed using Solidworks. This step required more time than originally thought, as drafting the bucket to the specifications provided proved difficult. From our system optimization using Engineering Equation Solver (EES), we selected a nozzle diameter of 0.8 inches. This diameter was selected based on minimal losses and high efficiencies, while staying below a gallon of water. From our Pelton bucket spreadsheet, the buckets were to be 2.8 inches wide and 2.02 inches tall. 20 buckets were required for a wheel ratio of 14. To minimize turbine weight, a bucket thickness of 0.05 inches was selected. A square arm, 1 inch in length that extended from the bucket, was to be clamped to a turbine wheel after the Figure 2. Single Pelton bucket that will translate water prototypes were complete. Having the jet stream to rotational power. buckets separate from the turbine housing allowed a detailed inspection of the buckets and easy access to any sanding needed later. The arm was designed as a rectangular box instead of a cylinder to ensure proper alignment when being attached to the wheel. After rapid prototyping was completed, the physical buckets required surface finishing inside the flow channel and reinforcement along the outer shell. A white lacquer was used for this process, a gel coating that was sandable and water resistant. Multiple layers were applied to strengthen buckets. After the lacquer dried, the insides of the buckets were sanded smooth, eliminating friction losses that would lower the power output of the turbine.
  4. 4. Figure 3. Application of lacquer to buckets. 8/994$) The nozzle was also designed in Solidworks and created using the rapid prototyping machine. The nozzle was to be simple and would be attached to the piping by an epoxy adhesive. In order to have a constant diameter jot stream exiting the nozzle, a ! inch horizontal section was added to the end of the nozzle to eliminate any vena contracta. The nozzle could be cut later if an increase in jet diameter was desired. The dimensions of the nozzle can be seen in Figure 4 below. Figure 4. Schematics of exit nozzle that will feed the Pelton turbine.
  5. 5. :;$$4)*$+',-) Originally our team planned to use a wheel similar to the one modeled in SolidWorks, seen to the right, which consisted of two discs with slots cut into them every 18 degrees. The discs were to sandwich the buckets into place. Material purchased was " inches thick MDF board, from which two discs of approximately 9 # in diameter were cut. After the slots were drilled using a mill and rotary apparatus, it was determined that the wheel would be too heavy and thus have too much rotational inertia. After this idea was scrapped, we Figure 5. Initial concept for wheel housing of buckets. consulted with Martin Koch of the IME department. Martin suggested cutting two disks out of a thin Plexiglas to sandwich the buckets. He provided a printer that laser cuts the Plexiglas based on an AutoCAD drawing provided by the user. We decided to cut two identical discs with slots aligned to the bucket placements. The slots were to hold support platforms for the buckets, also made out of Plexiglas cut from the laser printer. Problems occurred with alignment of the supports on the adjacent wheel. After carefully alignments, both discs were cured together using the Plexiglas supports and epoxy resin. Overall, we greatly reduced the turbine weight and rotational inertia, allowing quicker initial acceleration to our operational speed. Figure 6. Final Plexiglas wheel with attached supports prior to encloser.
  6. 6. Figure 7. Careful sanding before adhering buckets to the turbine wheel. ) <$+$1(/'1)2-0)+6==/1&)0$+',-) ) We chose a five-gallon drinking water container commonly seen on water coolers as our water reservoir. Since the neck of the bottle had a gradually converging profile (high r/D value), the entrance losses and head loss would be greatly reduced. The diameter of the bottle’s neck was approximately 1 " inches, leading our team to select PVC piping of equal diameter. Based on talks with members of previous teams, it was decided that the pipe should lie vertically straight, perpendicular to the ground. From a fluid mechanics standpoint, this would reduce the length of pipe, and therefore have the least head loss (smallest L/D value). Also, the largest diameter for flexible tubing available from Home Depot was 1 " inches. This was desired so the nozzle angle could be set correctly to 21 degrees from the horizontal, optimal for power output. Figure 8. PVC connector attached to water reservoir to link reservoir to PVC piping.
  7. 7. At the end of the straight length of pipe a 45 degree elbow was attached. To this a ! turn ball valve was attached. While the valve was initially difficult to turn, we practiced with the system numerous times to have a familiarity for the time needed to turn the valve. To the outlet of the ball valve, a small section of flexible 1 " inch tubing was attached. The flexible tubing had a natural curve to it. By cutting the tubing at precisely the right location, a nozzle angle of 21 degrees from the horizontal was obtained. The rapid prototyped nozzle was attached to flexible piping using epoxy and sealed with plumber’s epoxy putty, an extremely strong adhesive. The support of the reservoir system was not critical, however stability and strength were desired. We purchased four 4 foot long, 1/16 inch thick steel L shaped beams with 3/8 inch holes cut every inch to use as supports. Holding this together were 1/16 inch straight sections of steel and bolts. For extra stability, feet made of short 2X4’s were attached to the bottom of the support. Figure 9. Full view of turbine housing, reservoir support, and pipe in completed assembly. >61"'-$)?/6+'-,) For ease of manufacturing, the housing consisted of two sheets of clear Plexiglas held in place by four long (approximately 1 " ft) bolts. By using Plexiglas the wheel could be seen in operation, while the bolts allowed adjustments to the width of the housing. The pulley was placed on the outside of the housing as not to interfere with the water exiting the buckets of the wheel. The housing was not attached to the reservoir support to allow rooms for adjustments and modifications, as well as ease of transportation to the competition.
  8. 8. Figure 10. Assembly of the turbine and pulley inside the turbine housing. Through the center of both sheets we drilled a 0.875-inch diameter hole, where we permanently fixed ball type bearings from a roller skate wheel. A 5/16-inch diameter shaft was allowed to freely rotate inside the bearings. The wheel and pulley were secured onto the shaft on the inside and outside of the housing respectively. Figure 11. Wheel and nozzle as seen through Turbine Housing. 3644$@)*$+',-) We decided that at full speed, a pulley diameter of nine inches would suffice. However, the required starting torque for a nine-inch pulley was a concern. Therefore, we designed a variable radius pulley such that the initial diameter was about 2 inches and increased
  9. 9. incrementally after about ! a turn to 9 inches. The diameter remained constant thereafter. The design was a composite material consisting of a plywood disk, short lengths of dowels inserted in to drilled holes, masking tape, Gorilla Glue and plumbers epoxy putty. Figure 12. Variable diameter pulley allowed less torque required to start the turbine. <$+64&+) After assembly of the system, we completed dozens of test trials to correct any problems with the system. Results from our own testing before the competition averaged around 1.6 seconds to 1.8 seconds, a decent time. Figure 13. Test run picture used to analyze path of flow with turbine. From this picture we concluded that the nozzle was positioned correctly.
  10. 10. In our initial run on Thursday, we placed with a time of 1.75 seconds and lost in our first match. While we were pleased with the consistency of performance, we brainstormed modifications to improve performance of the system we already had. The water reservoir’s height was increased one inch to the maximum height level of 4 feet 3 inches. It was evident during test runs that we used far less than one gallon of water. To increase the power output of the system, we cut the nozzle back to an inside diameter of 0.9 inches. The vena contracta was analyzed, using Figure 14 below, to reveal a 12.5 percent reduction in diameter at location D2. From this figure we also found that the closer the nozzle is to the Pelton bucket, the less reduction happens to the flow diameter. We moved the nozzle as close as possible to the Pelton buckets by adjusting the width of the turbine housing. Several more trials were conducted with our updated system. We improved our quickness in opening the valve with each practice run. Our trial times increased significantly to between 1.2 to 1.4 seconds. Figure 14. Test run showing the vena contracta, where the water jet diameter is reduced as it travels further from the nozzle exit. On the second day of competition, our turbine won the first round matchup with a time of 1.39 seconds. Our second round matchup was lost when the string, attached from pulley to garbanzo bean can, fell off the pulley track before the finish line. Upon further examination, the cause of the pulley malfunction may be due to how the string was tied down on the pulley. The string is tied to a peg about two inches from the shaft driven by the turbine. After each run, the string is cut to break the can from the turbine. Several loops of string had accumulated on the peg from several trial runs. This resulted in our team attaching the new loop for the last run too high on the peg, leading the string off the pulley. In order to correct this problem, the remaining loops should be cut and the lip on the pulley should be heightened.
  11. 11. ./-%46+'/- Overall we have learned quite a bit this quarter working on the hydraulic turbine project. It has been interesting to see the path of design in respect to turbines, especially having the ability to take an idea from conception to realization in a physical product that must meet specification. The project has taught us how to work as a team and how to utilize each other’s strengths as mechanical engineers to effectively complete the project.

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