The purpose of the impact of jet experiment is to design a system to determine the force generated by the impact of jet on a variety of target vanes. A formula is given to calculate the reaction force at the different vanes caused by the jet. At the end of the experiment, the data collected and results calculated will then be compared to theoretical values which are given. Students are expected to be able to come to a conclusion regarding the relationship between the reaction force produced at the target vanes and the angle where the shape of the vanes curve.
There are many ways to produce mechanical work from fluid under pressure. One of the famous ways is to use the pressure to accelerate the fluid to a high velocity in a jet. Over the years, engineers have found many ways to utilize the force that can be produced by a jet of fluid on a surface diverting the flow. For example, the pelton wheel has been used to make flour. Firemen make use of the kinetic energy stored in a jet to deliver water above the level in the nozzle to extinguish fires in tall buildings. Fluid jets are also used in industry for cutting metals and debarring. This goes to show the importance of applications of the fluid jet in the technological aspects of various fields in our society. This experiment aims at assessing the different forces exerted by the same water jet on a variety of geometrically different plates. A ‘jet impact apparatus’ is used to carry out this experiment whereby three vanes of different geometrical properties are used. The results obtained experimentally are to be compared with the ones inferred from theory through utilizing the applicable versions of the Bernoulli and momentum equations.
2.0 EXPERIMENTAL DESIGN
1. The Jet Impact Apparatus ( as shown in the figure )
2. Volumetric Hydraulic Bench/Water
3. 3 different shape of vanes; Flat Plate, Conical Cup, and Hemispherical Cup 4. Stop Watch
The water is supplied to the jet apparatus in a closed loop by a pump. The flow rate is determined with the use of a weighing tank, and a stopwatch. The water issues vertically upwards into the air, through a nozzle. The three target vanes are as follows: * A flat plate
* Hemispherical cup
* Conical cup
Each object can be mounted on a horizontal lever above the water jet and receive its impact. The speed of water pumped out from the nozzle is adjusted until the tally is returned to the balanced position. To find the flow rate of water, mass of water collected, time for collection of water and mass of the jockey weight is recorded.The results are calculated and tabulated into a table. Graphs are made for comparison of different shapes of vanes and the experimental and theoretical results.
1. Then, the apparatus is leveled and the lever set is set to the balanced position (as indicated by the tally) with the jockey weight placed at its zero position. This step is carried out using the flat plate as the target vane. 2. Water is admitted through the bench supply valve. The rate of flow is then increased to the maximum and the position of the jockey weight which restores the lever to the balanced position is noted, while the discharge is weighed in the weighing tank. 3. A series of about four readings with roughly equally spaced positions of the jockey weight (15cm, 30cm, 45cm and 60cm), are then taken by increasing the flow rate from the bench. (The time is recorded for 5kg of water collected in the weighing tank.) 4. The experiment is repeated using conical cup and hemispherical cup. 5. The diameter of the nozzle, the height of the vane above the tip of the nozzle when the lever set (tally) is balanced, the distance between the center of the vane and the pivot of the lever and the jockey weight are measured and recorded.
3.0 RESULTS AND DISCUSSIONS
TABLE 1: HEMISPHERICAL CUP
References: * Massey, B.S. (1989). Mechanics of Fluids. 6th Ed, Chapman & Hall.
* White F.M.(1994). Fluid Mechanics. 3rd Ed., McGraw-Hill.
* Van Dyke M.(1982).An Album of Fluid Motion. Parabolic Press.
* Coulson, J.M.; and Richardson, J.F. Chemical Engineering, Volume 1. 6th Ed.,Butterworth-Heinemann.
* web.cecs.pdx.edu.(No date). Impact of A Jet. Available at: http://web.cecs.pdx.edu/~gerry/class/EAS361/lab/pdf/lab4_impactOfJet.pdf [Accessed 15 May 2013]
* codecogs.com. (No date). Impact of jets. Available at: http://www.codecogs.com/reference/engineering/fluid_mechanics/jet/impact_of_jets.php [Accessed 15 May 2013]
* http://staff.fit.ac.cy. (No date). Impact of A Jet. Available at: http://staff.fit.ac.cy/eng.fm/classes/amee202/Fluids%20Lab%20Impact%20of%20a%20Jet.pdf [Accessed 15 May 2013]
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