Impact of Jet free essay sample

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. 1. 1 INTRODUCTION 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. This helps us to understand how forces can affect the change of momentum flow in the jet. The theoretical jet force can be calculated from the principle of linear momentum. The density of water is 1kg/L. The results obtained are to be compared with the theoretical values. To produce mechanical work from fluid under pressure, we use the pressure to accelerate the fluid to a high velocity in a jet. The application of this principle can be seen surrounding us. For example, water turbines are used to generate power in our country. Another example is that the kinetic energy stored in a jet is used by the firemen to deliver water above the level in the nozzle to extinguish fires in tall buildings. And also, the pelton on wheel is used to make flour. 3. 0 APPARATUS i. HM150 impact of jet a) Loading weights b) Lever mechanism c) Deflector d) Nozzle e) Perspex vessel f) Drain connection g) Base plate. Inlet connection ii. Various deflector Plate Hemisphere Slope Cone iii. A set of weights iv. Stop watch 3. 1 PROCEDURES 1) A quick inspection is performed to ensure that the units is in proper operating condition. 2) A hose connection made and the unit is connected to the nearest power supply. 3) The discharge pipe is opened. 4) One of the deflectors (plate, hemisphere, slope or cone) is assembled. The three screws (3) on the cover (4) is loosen. The cover is removed together with the lever mechanism. 5) An appropriate deflector is fitted. The lock nut (2) on the rod is tightened. The cover is screwed back onto the vessel. Adjusting screw (5) is used to set pointer to zero (7). Any loading weights are not placed on measurement system when doing so. 7) The desired loading weight :0. 2N, 0. 3N, 1N, 2N, and 5N is applied. 8) The main clock is closed. 9) The pump is switched and the main cock is opened carefully until pointer is on zero again. 10) The drain cock is closed and the volumetric flow rate is determined by using stopwatch to establish time required for raising the level in the volumetric tank from 20 to 30 liters. 11) The pump is switched off and the drain is opened. In this experiment, hemisphere deflector has the lowest flow rate among the deflectors used. This indicates that hemisphere deflectors are the most efficient to be used in water turbines. The calculated forces for each deflector are different from the measured forces. The comparison between calculated force and measured force for each deflectors is stated in the table below : Example value :1 N Calculated force, Fth in N Measured force, F in N Plate 0. 67 1. 0 Hemisphere 0. 92 1. 0 Slope 2. 77 1. 0 Cone 1. 19 1. 0 To calculate the percentage of error: Percentage of error = Theoretically, the calculated force is supposed to be the same as the measured force. The percentage of error in this experiment ranged from 3% to 177%. The difference between the calculated force and measured force is due to some errors made throughout the experiment. For example, when setting the pointer, due to parallax error, the pointer may not be set to zero precisely. Next, when adjusting the main cock, error might be made. The main cock may not properly open thus causing the pointer not exactly at zero. Another possibility is that when measuring the water level raise from 10 L to 20 L, parallax error might occured. To improve the accuracy of this experiment,we may repeat the steps to get consistent values. In order to improve the errors, when setting the pointer, make sure the eye level is at the same level with the pointer to ensure it is set to zero accurately. Next, make sure the main cock is properly open by double checking it. Reading on volumetric tank should be on the water meniscus to avoid parallax error. We also must make sure the control valve is completely close before the pump is switched on in order to avoid intrusion of air into the pump. Entrapped air may reduce the exerted force of the jet. Conclusion In conclusion, the momentum equation is verified experimentally through this experiment. The calculated force is supposed to be the same as measured force. But in this experiment, the difference between the calculated force and the measured force may due to some errors made during the experiment. In this experiment, the hemisphere deflector has the lowest flow rate and takes longer time for the volumetric tank to rise from 10 L to 20 L compared to the other deflectors. Therefore hemisphere deflector is the most efficient to be used in water turbine.