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THE IMPACT OF JET APPARATUS

ABSTRACT

This project is focused on experimental analysis of impact of water jet on vanes. This work intends to predict the output of a pelton wheel, and to determine its optimum rotational speed. Hence this work explains how the deflection of the jet generates a force on the buckets, and how the force is related to the rate of momentum flow in the jet. In this experiment, we measure the force generated by a jet of water striking a flat plate or a hemispherical cup, and compare the results with the computed momentum flow rate in the jet.  The experiment is shown in the arrangement, in which water supplied from the Hydraulic Bench is fed to a vertical pipe terminating in a tapered nozzle. This produces a jet of water which impinges on a vane, in the form of a flat plate or a hemispherical cup.

CHAPTER ONE

INTRODUCTION

1.1  BACKGROUND OF THE PROJECT

Over the years, engineers have found many ways to utilize the impact force of fluids. For example, the Pelton wheel has been used to make flour. Further, the impulse turbine. Firemen make use of the kinetic energy stored in a jet to extinguish fires in high-rise buildings. Many other applications of fluid jets can be cited which reveals their technological importance. This experiment is designed to study the force that can be impacted by a jet of fluid on a surface diverting the flow (Khurmi, 2010). The history of the equipment “impact of jet apparatus” is traced back to the 19thcentury. The apparatus is used to demonstrate the way a certain type of water turbine, the pelton wheel can extract water from a fast jet of water, which is similar to the way in which a space craft increases or decreases its kinetic energy by swinging around a moving plant.  Nevertheless, water turbines are used to generate power like in pelton wheel produced by an American engineer Lester A Pelton. Engineer Lester Pelton was born in the year 1892 in Vermilion Ohio on the shores of Lake Erie.

The invention came about when water was an under used resource and before electricity was economically practical as a motive power. The first turbine built by pelton was in Campton Ville. In Campton Ville, by the time search for gold progressed, which required power to drive stamp mills that crush the ore and pump air into mine turnnels and later to provide electricity and compressed air. Some mines used steam engines but these required a large and constant supply of fire wood. Therefore, instead of the slow water wheel traditionally used by flour mills which needed only a moderate height but used a large quantity of water, even mine owners installed turbine wheels with cups around their circumference with a fast jet of water coming from a reservoir high up (Moth, 2009).

Pelton invention started from an accidental observation when he was watching a spinning water turbine when the key holding its wheel onto its shaft slipped causing it to be misaligned. Instead of the jet hitting the wheel at the middle, the slip made it hit near the edge thus causing the wheel to spin faster. It is known that the Pelton wheel is suitable for conditions which require a 100m head of water and a flow rate which could be used to develop about 900kW of power. Over 40 years ago, the concept of performing simple experiments in hydraulics on hydraulic bench was first introduced in the University of Notingham, since then, hydraulic bench has been in use to conduct experiments with the impact of jet apparatus. Moreover, there is need to understand how the deflection of a jet generates a force on the buckets and also to know how the force is related to the rate of change of momentum in the jet before a prediction could be made on the use of Pelton wheel (Orga and Ujam, 2005).

1.2  AIM AND OBJECTIVES

The aim of this project is to investigate the impact of jet apparatus. Hence, the objectives are as follows;

1. To experiment, demonstrate and verify the integral momentum equation. The force generated by a jet of water deflected by an impact surface is measured.

2. To study the relation between the force produced and the change of momentum when a jet strikes a vane and compare between force exerted by a jet on a flat plate and hemispherical surface.

3. To examine the momentum transfer (ergo, force transmitted) from a fluid to object of various forms. In particular, the study looks at the momentum transfer as a function of the angle through which the fluid stream was deflected. By varying a fluid stream’s deflection angle, up to twice the original momentum of the stream can be transferred to the object.

4. To demonstrate the applicability of Newton’s law of motion to a fluid, to investigative the effect of a jet flow on different shaped targets, comparing the theoretical predictions with actual measurements.

1.3 IMPORTANCE OF IMPACT OF JET APPARATUS

Impact of jet apparatus is used in the laboratory to demonstrate the way in which fluid force is being used to generate a force that can turn a turbine; that is converting the kinetic energy in a flowing fluid from  a nozzle to a rotary motion of the turbine with the help of vanes fitted o shaft of the turbine. The jet is directed to vane of turbine wheel that is rotated by the force generates due to change of momentum of the fluid according to Newton’s second law of motion. The principle is used in designing impulse turbine; part of the fluid energy is transformed to kinetic energy in a nozzle that issues a jet of fluid at high speed. Impulse turbine have been constructed to generate power up to 100-mega watt or more with efficiencies greater than 85%. In the impact of jet apparatus, a jet of water issuing from a nozzle strikes a target. The force generated equals the rate of change of the linear momentum particulars from the jet.

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