CONSTRUCTION AND EXPERIMENTAL STUDY OF A PELTON TURBINE A Thesis submitted to the Department of Mechanical & Production Engineering
AHSANULLAH UNIVERSITY OF SCIENCE & TECHNOLOGY BY Istiak Ahmed [11.01.08.021] Saima Akter Liza [11.01.08.035] Mohammad Zaber Bin Ismaeel [11.01.08.020]
Under the supervision Of Mr. Mahbubul Muttakin In partial fulfillment of the Requirement for the Degree Of Bachelor of Science in Mechanical Engineering June 2015
ACKNOWLEDGEMENT Since this program has been carried out as a thesis in partial fulfillment of the requirement for the degree of Bachelor of Science in Mechanical Engineering of Ahsanullah University of Science and Technology (AUST), we are thankful to our university for its support. Offering the deepest appreciation to our supervisor, Mr. Mahbubul Muttakin for his kind and generous guidance throughout the thesis. We are indebted to Dr. Dewan Hasan Ahmed for his help and suggestion. We are thankful to Md. Faysal Khan and Md. Minal Nahin for their precious propositions. Mr. Sirajul Islam, Mr. Abdul Awal and Md. Shorif without them the thesis might be incomplete. Truly relieved by their help and support. We are obliged to our friends Shafayat Sourov, Rakibul Hasan, Fahmid Hasan, Rafikur Rahman Bijoy, Enamul Hasib who never hesitated in supporting us, morally and technically. Encouragement, help and patience of family members which kept us inspired and hopeful throughout the work and especially at the time of crisis; we would like to thank them, deeply and sincerely.
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ABSTRACT The thesis includes a literature survey of Pelton turbine, incorporating a historical review. Pelton hydraulic turbines are impulse-type turbo machines commonly used in hydroelectric plants with medium-to-high water head and in various energy recovery applications. This turbine more specifically Pelton wheel will be used to do lab experiment in Fluid Machinery Laboratory. The aim of the present work is to provide detailed performance measurements on a Pelton turbine model, along with the design and geometrical dimensions of its runner/buckets and nozzle. The measurements include the net water head, flow rate and the torque and rotation speed of the runner, from which the corresponding efficiency and shaft power are computed. Flow is varied and head is measured for each variance to calculate the power in the system. Other parameters necessary for the study are also measured and recorded for the study. The results are presented in graphical method and the properties of the graph are used to discuss the properties of the turbine under study. The Pelton wheel under study is of a smaller scale though it acts as a representative of a similar system in large scale.
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TABLE OF CONTENTS Page No.
ACKNOWLEDGEMENT ................................................................................................ i ABSTRACT ...................................................................................................................... ii TABLE OF CONTENTS ................................................................................................ ii NOMENCLATURE ........................................................................................................ vi LIST OF FIGURES ....................................................................................................... vii LIST OF TABLES .......................................................................................................... ix CHAPTER 1 ..................................................................................................................... 1 INTRODUCTION .......................................................................................................... 1 CHAPTER 2 ..................................................................................................................... 4 LITERATURE REVIEW ............................................................................................... 4 2.1 Water Wheels: ...................................................................................................... 4 2.1.1Types of Water Wheels:.................................................................................. 4 2.2 Turbine: ................................................................................................................ 7 2.2.1 Types of Turbine: ........................................................................................... 8 2.3 Hydraulic Turbines: ............................................................................................ 10 2.3.1Classification: ............................................................................................... 10 2.3.2 Pelton Wheel: ............................................................................................... 11 2.3.3 Background of Pelton Wheel: ...................................................................... 11 2.4 Advantages of Pelton Wheel: ............................................................................. 13 2.5 Comparison with other turbines: ........................................................................ 13 2.6 Uses of Pelton Wheel: ........................................................................................ 13
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Chapter 3 ........................................................................................................................ 15 Theory .......................................................................................................................... 15 3.1 Working principle of pelton wheel: .................................................................... 15 3.2 Working Proportions for Design of Pelton Wheel: ............................................ 18 3.3 Pelton turbine losses and efficiencies: ................................................................ 22
CHAPTER 4 ................................................................................................................... 25 EXPERIMENTAL SETUP .......................................................................................... 25 4.1 Full setup: ........................................................................................................... 25 4.2 Design: ................................................................................................................ 27 4.2.1 Bucket: ......................................................................................................... 27 4.2.2 Rim:.............................................................................................................. 27 4.2.3 Shaft: ............................................................................................................ 28 4.2.4 Wheel Casing: .............................................................................................. 28 4.2.5 Brake Drum:................................................................................................. 30 4.2.6 Supporting Table:......................................................................................... 30 4.2.7 Disposal bucket: ........................................................................................... 31 4.3 Equipments: ........................................................................................................ 32 4.3.1 Pressure Gauge: ........................................................................................... 32 4.3.2 Flow Meter: .................................................................................................. 33 4.3.3 Tachometer: ................................................................................................. 34 4.3.4 Stop watch:................................................................................................... 34 4.3.5 Spring Balance: ............................................................................................ 35 4.4 Construction: ...................................................................................................... 36 4.4.1 Construction of penstock: ............................................................................ 36 iv
4.4.2 Nozzle: ......................................................................................................... 37 4.4.3 Runner: ......................................................................................................... 38 4.4.4 Wheel casing: ............................................................................................... 40 4.4.5 Torque measurement arrangement:.............................................................. 41 4.4.6 Supporting table: .......................................................................................... 42 4.4.7 Water disposal:............................................................................................. 42 CHAPTER 5 ................................................................................................................... 44 EXPERIMENTAL DATA COLLECTION & CALCULATION ............................... 44 5.1 Experimental procedures: ................................................................................... 44 5.2 Data Table: ......................................................................................................... 45 5.3 Calculation: ......................................................................................................... 46 5.3.1 Sample calculation: ...................................................................................... 46 CHAPTER 6 ................................................................................................................... 49 RESULT & DISCUSSION: ......................................................................................... 49 6.1 Calculation Table:............................................... Error! Bookmark not defined. 6.2 Graphs & Discussion: ......................................................................................... 50 6.2.1 Head vs. Flow rate: ...................................................................................... 50 6.2.2 Speed vs. Flow rate: ..................................................................................... 51 6.2.3 Torque vs. Flow rate: ................................................................................... 52 6.2.4 Output power vs. Flow rate:......................................................................... 53 6.2.5 Output power vs. Input power curve: .......................................................... 54 CHAPTER 7 ................................................................................................................... 56 CONCLUSION: ........................................................................................................... 56 REFERENCES ............................................................................................................... 58
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NOMENCLATURE Symbol
Description
unit
Bb
Width of the bucket
m
Cv
Co-efficient of velocity
N/A
Db
Depth of the bucket
m
D
Mean diameter of the wheel
m
d
Diameter of jet
m
H
Head
m
Lb
Length of the bucket
m
m
Jet ratio
N/A
N
Speed of the wheel
rpm
Ns
Specific speed
rpm
P
Pressure
Pa
Pi
Inlet power
Watt
Po
Outlet power
Watt
Q
Flow rate
m3/s
T
Torque
N.m
u
Peripheral speed of rotor
m/s
v
Velocity
m/s
va
Actual velocity of jet
m/s
z
No. of buckets
N/A
γ
Specific weight of water
N/m3
φ
Speed ratio
N/A
𝜔
Angular speed of the wheel
rad/s
𝜂
Efficiency
%
𝜌
Density of water
kg/m3
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LIST OF FIGURES Page no. Figure 1.1The configuration of the nozzle and buckets in a Pelton wheel .............................1 Figure 1.2General arrangement of the Pelton wheel ..............................................................2 Figure 1.3Water strike on Pelton wheel ..................................................................................3 Figure 2.1Overshot water wheel .............................................................................................5 Figure 2.2 Undershot water wheel ..........................................................................................6 Figure 2.3 Breast water wheel ................................................................................................7 Figure 2.4 Schematic of Impulse and Reaction turbines with pressure and velocity graph. ..9 Figure 2.5 Turbine classification ..........................................................................................10 Figure 2.6 Pelton's original patent (October 1880). ..............................................................12 Figure 3.1 Pelton wheel working procedure .........................................................................16 Figure 3.2 Velocity diagram of Pelton wheel .......................................................................17 Figure 3.3 Dimensions of Bucket. ........................................................................................20 Figure 3.4 Schematic layout of hydro plant ..........................................................................22 Figure 3.5 Efficiency vs. speed at various nozzle settings. ..................................................23 Figure 3.6 Power vs. speed of various nozzle setting. ..........................................................24 Figure 3.7 Pelton turbine losses and efficiencies ..................................................................24 Figure 4.1 Front View of upper portion of the Setup ...........................................................25 Figure 4.2 Back View of upper portion of the setup.............................................................25 Figure 4.3 Showing the torque measurement arrangement of the setup and nozzle position...26 Figure 4.4 Isometric view of full setup .................................................................................26 Figure 4.5 Bucket ..................................................................................................................27 Figure 4.6 Rim ......................................................................................................................27 Figure 4.7 Shaft .....................................................................................................................28 Figure 4.8 Front View of Casing ..........................................................................................28 Figure 4.9 Orthographic View of casing...............................................................................29 Figure 4.10 Solidworks view of casing.................................................................................29 Figure 4.11 Solidworks view of Brake drum ........................................................................30 Figure 4.12 Solidworks view of supporting table .................................................................30 vii
Figure 4.13 Solidworks view of disposal bucket ..................................................................31 Figure 4.14 Pressure gauge ...................................................................................................32 Figure 4.15 Flow Meter ........................................................................................................33 Figure 4.16 Flow error curve ................................................................................................33 Figure 4.17 Digital Tachometer ............................................................................................34 Figure 4.18 Stop watch .........................................................................................................34 Figure 4.19 Spring Balance...................................................................................................35 Figure 4.20 GI pipe ...............................................................................................................36 Figure 4.21 Different types of fittings ..................................................................................36 Figure 4.22 Penstock (pipeline) ............................................................................................37 Figure 4.23 Nozzle ................................................................................................................37 Figure 4.24 Nozzle arrangement ...........................................................................................38 Figure 4.25 Bucket ................................................................................................................39 Figure 4.26 Runner assembly ...............................................................................................39 Figure 4.27 construction of casing ........................................................................................40 Figure 4.28 Torque measurement arrangement ....................................................................41 Figure 4.29 Supporting table frame ......................................................................................42 Figure 4.30 Disposal bucket .................................................................................................43 Figure 4.31 Disposal route equipments ................................................................................43 Figure 4.32 Disposal pipeline ...............................................................................................43 Figure 5.1 Head vs. Flow rate curve .....................................................................................50 Figure 5.2 Speed vs. Flow Rate curve ..................................................................................51 Figure 5.3 Torque vs. Flow rate curve ..................................................................................52 Figure 5.4 Output power vs. Flow rate curve .......................................................................53 Figure 5.5 Output power vs. Input power .............................................................................54
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LIST OF TABLES Page no. 5.1 Data Table .............................................................. Error! Bookmark not defined. 6.1 Calculation Table ...................................................................................................49
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CHAPTER 1 INTRODUCTION A Pelton wheel is a tangential flow impulse hydraulic machine that is actively used for the production of power from kinetic energy of flowing water. It is the only form of impulse turbine in common industrial use. It is a robust and simple machine that is ideal for the production of power from low volume water flows at a high head with reasonable efficiency. The Pelton wheel constructed in this thesis reproduces all the characteristics of full size machines and allows an experimental program to determine the performance of a turbine. Impulse turbines operate through a mechanism that first converts the high head through a nozzle into high velocity, which strikes the buckets at a single position as they pass by. These turbines are suited for relatively low power and high head derivations. The Pelton wheel is comprised of three basic components that include the stationary inlet nozzle, the runner and the casing. The multiple buckets are mounted on a rotating wheel. They are shaped in a manner that divides the flow in half and deflects the water by an angle of 180o. The nozzle is positioned in a similar plane as the wheel and is arranged so that the jet of water impinges tangentially on to the buckets. The nozzle is controlled by a ball valve regulator.
Figure 1.1: The configuration of the nozzle and buckets in a Pelton wheel
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A friction dynamometer consists of a 8inch diameter brake wheel fitted with a fabric brake band which is tensioned by a weight hanger and masses with the fixed end being secures via a spring balance to the support frame. A tachometer may be used to measure the speed of the turbine.
Figure 1.2: General arrangement of the Pelton wheel
The runner of the Pelton turbine consists of double hemispherical cups fitted on its periphery. The jet strikes these cups at the central dividing edge of the front edge. The central dividing edge is also called a splitter. The water jet strikes edge of the splitter symmetrically and equally distributed into the two halves of hemispherical bucket. The inlet angle of the jet is therefore between 1o and 3o. Theoretically if the buckets are exactly hemispherical it would deflect the jet through 180°. Then the relative velocity of the jet leaving the bucket would be opposite in direction to the relative velocity of the jet entering. This cannot be achieved practically because the jet leaving the bucket then strikes the back of the succeeding bucket and hence overall efficiency would decrease. Therefore in practice the angular deflection of the jet in the bucket is
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united to about 165° or 170°. And the bucket is slightly smaller than a hemisphere in size. The amount of water discharges from the nozzle is regulated by a ball valve.
Figure 1.3: Water strike on Pelton wheel
Objectives:
To construct a Pelton Turbine with proper design and to analyze its performance under different static heads.
To demonstrate about Pelton wheel for study in fluid machinery lab.
To determine the performance characteristics values using experimental procedure.
To find the performance characteristics curve i.e. to ploti.
Head vs. Flow rate
ii.
Speed vs. Flow rate
iii.
Torque vs. Flow rate
iv.
Output power vs. Flow rate
v.
Output power vs. input power
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CHAPTER 2 LITERATURE REVIEW
2.1 Water Wheels: From early times, people started using water wheels to convert hydraulic energy into mechanical energy by water wheels. However, the efficiency of these water wheels was very low in comparison to modern turbines. Water wheels consist of a circular frame with a number of buckets,
the wheel
is
rotated. The speed of the wheel
is
comparatively low.
2.1.1Types of Water Wheels: There are different types of water wheels. Some important water wheels are mentioned below. -Overshot water wheel -Undershot water wheel -Breast water wheel Overshot water wheel: A vertically mounted water wheel that is rotated by falling water striking paddles, blades or buckets near the top of the wheel is said to be overshot. In true overshot wheels the water passes over the top of the wheel, but the term is sometimes applied to backshot or pitchback wheels where the water goes down behind the water wheel. A typical overshot wheel has the water channeled to the wheel at the top and slightly beyond the axle. The water collects in the buckets on that side of the wheel, making it heavier than the other "empty" side. The weight turns the wheel, and the water flows out into the tailwater when the wheel rotates enough to invert the buckets. The overshot design can use all of the water flow for power (unless there is a leak) and does not require rapid flow.
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Unlike undershot wheels, overshot wheels gain a double advantage from gravity. Not only is the momentum of the flowing water partially transferred to the wheel, the weight of the water descending in the wheel's buckets also imparts additional energy. The mechanical power derived from an overshot wheel is determined by the wheel's physical size and the available head, so they are ideally suited to hilly or mountainous country. On average, the undershot wheel uses 22 percent of the energy in the flow of water, while an overshot wheel uses 63 percent, as calculated by English civil engineer John Smeaton in the 18th century.
Figure 2.1: Overshot water wheel
Undershot water wheel: An undershot wheel (also called a stream wheel) is a vertically mounted water wheel that is rotated by water striking paddles or blades at the bottom of the wheel. The name undershot comes from this striking at the bottom of the wheel. This type of water wheel is the oldest type of wheel. It is also regarded as the least efficient type, although subtypes of this water wheel (e.g. the Poncelet wheel,Sagebien wheel and Zuppinger wheel) allow somewhat greater efficiencies than the traditional undershot wheels. The advantages of undershot wheels are that they are somewhat cheaper and simpler to build, and have less of an environmental impact—as they do not constitute a major change of the river. Their disadvantages are—as mentioned before—less efficiency, which means that they generate less power and can only be used where the flow rate is sufficient to provide torque.
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Undershot wheels are also well suited to installation on floating platforms. The earliest were probably constructed by the Byzantine general Belisarius during the siege of Rome in 537. Later they were sometimes mounted immediately downstream from bridges where the flow restriction of arched bridge piers increased the speed of the current.
Figure 2.2: Undershot water wheel
Breast water wheel: A vertically mounted water wheel that is rotated by falling water striking buckets near the center of the wheel's edge, or just above it, is said to be breastshot. Breastshot wheels are the most common type in the United States of America and are said to have powered the American industrial revolution. Breastshot wheels are less efficient than overshot wheels (see below), are more efficient than undershot wheels, and are not backshot. The individual blades of a breastshot wheel are actually buckets, as are those of most overshot wheels, and not simple paddles like those of most undershot wheels. A breastshot wheel requires a good trash rack and typically has a masonry "apron" closely conforming to the wheel face, which helps contain the water in the buckets as they progress downwards. Breastshot wheels are preferred for steady, high-volume flows such as are found on the fall line of the North American East Coast.
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Figure 2.3: Breast water wheel
2.2 Turbine: A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels. Gas, steam, and hydraulic turbines have a casing around the blades that contains and controls the working fluid. Credit for invention of the steam turbine is given both to the British engineer Sir Charles Algernon Parsons (1854–1931), for invention of the reaction turbine and to Swedish engineer Gustaf de Laval (1845–1913), for invention of the impulse turbine. Modern steam turbines frequently employ both reaction and impulse in the same unit, typically varying the degree of reaction and impulse from the blade root to its periphery. The word "turbine" was coined in 1822 by the French mining engineer Claude Burdin from the Latin turbo, or vortex, in a memo, "Des turbines hydrauliques ou machines rotatoires à grande vitesse", which he submitted to the “Académie royale des sciences” in Paris. Benoît Fourneyron, a former student of Claude Burdin, built the first practical water turbine.
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2.2.1 Types of Turbine: Turbines may be of different types and are named according to the mode or media through which they are made to rotate. Some commonly used turbines are: 1. Steam Turbine: When the turbine receives its rotating force from powerful steam jets. 2. Hydraulic Turbine: When the turbine is rotated by impact of accumulated water falling from a high altitude (from over a dam or barrage constructed on rivers for this purpose), it is called a hydraulic turbine. 3. Gas Turbine: When the turbine receives its rotating force from high pressure gas (by burning coal, natural gas etc.) ejected from nozzles called a gas turbine.
Types of turbine according to working principle: The turbine is, according to its working principle, of 2 types. These are: 1. Impulse Turbine 2. Reaction Turbine
1. Impulse turbine: In this type, a powerful working fluid jet from no. of nozzles, strikes the cups or buckets on the periphery of the turbine wheel thereby causing the wheel to rotate. That means, the turbine rotates due to impulse (force) of fluid jet. 2. Reaction turbine: Ideally, in this type of turbine, a closed drum or a cylinder is arranged the shaft and on the periphery of the drum some nozzles are arranged at right angles (cross) to the shaft instead of cups or buckets, as shown in figure. High pressure fluid from a boiler enters the drum at one end and this fluid when escaping through the nozzles exerts heavy back pressure on the body of the nozzles. Due to this back pressure, the drum rotates (backward) along with the shaft. In other words, this type of turbine rotates due to ‘reaction’ and so is called the reaction turbine. Practically, no pure reaction turbine exists. It may be mentioned here that the reaction type 8
turbine produces very small power and its uses and applications are limited to small power plants only.
Figure 2.4: Schematic of Impulse and Reaction turbines with pressure and velocity graph.
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2.3 Hydraulic Turbines: Hydraulic turbines are the machines which converts the hydraulic energy into mechanical energy. The mechanical energy produced by the hydraulic turbine can be converted into electrical energy by coupling the turbine to an electric generator.
Turbine
Impulse
Reaction
Pelton wheel
Radial flow
Inward flow
Mixed flow
Axial flow
Outward flow
Kaplan turbine
Francis turbine Figure 2.5: Turbine classification
2.3.1Classification: Classification according to the following criteria:
Hydraulic action: Impulse & Reaction turbine.
Direction of flow of water: Tangential, Radial, Axial & Mixed.
Direction of flow of water: Vertical & Horizontal turbine.
Head: Low, Medium & High Head turbine.
Specific speed: Low, Medium & High Specific Speed Turbine
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Propeller turbine
2.3.2 Pelton Wheel: Hydraulic action: Impulse (total head converted into K.E.), Direction of flow of water: Tangential flow, Direction of the shaft: Horizontal, Head: High head (150m~2000m), Specific speed: Low specific speed (Sp. Speed 60)
2.3.3 Background of Pelton Wheel: Lester Allen Pelton (1829-1908) is the inventor of Pelton Water Wheel. Lester A. Pelton was an American inventor who successfully developed a highly efficient water turbine, for a high head, but low flow of water operating in many situations. Most notable today the hydroelectric power stations. Little is known of his early life. Pelton embarked on an adventure in search of gold. He came to California from Ohio in 1850, he was 21 years old. In 1864, after a failed quest for gold he was working in the gold mines as a millwright, and carpenter at Campton Ville, Yuba County, California. It was here that he made a discovery which won for him a permanent place in the history of water power engineering. In the mines, Pelton saw water wheels were being used to provide mechanical power for all things mining, air compressors, pumps, stamp mills and operating other machines. The energy to drive these wheels was supplied by powerful jets of water which struck the base of the wheel with flat-faced vanes. These vanes eventually evolved into hemispherical cups, with the jet striking at the center of the cup on the wheel. Pelton further observed that one of the water wheels appeared to be rotating faster than other similar machines. It turned out initially that this was due to the wheel had come loose, and moved a little on its axle. He noticed the jet was striking the inside edge of the cups, and exiting the other side of the cup. His quest for improvement resulted in an innovation. So, Pelton reconstructed the wheel, with the cups off center only to find again that it rotated more rapidly. Pelton also found that using split cups enhanced the effect. By 1879, he had tested a prototype at the University of California, which was successful. He was granted his first patent in 1880.
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By 1890, Pelton turbines were in operation, developing thousands of horsepower, powering all kinds of equipments. In 1889, Pelton was granted a patent with the following text. "Pelton water turbine or wheel is a rotor driven by the impulse of a jet of water upon curved buckets fixed to its periphery; each bucket is divided in half by a splitter edge that divides the water into two streams. The buckets have a two-curved section which completely reverses the direction of the water jet striking them."
Figure 2.6: Pelton's original patent (October 1880).
The first wheel that Pelton put to practical use was to power the sewing machine of his landlady, Mrs. W. G. Groves in Campton Ville. This prototype wheel is on display at a lodge in Campton Ville. He then took his patterns to the Allan Machine Shop and Foundry in Nevada City. Wheels of various types and sizes were made and tested. Hydro-electric plants of thousands of horsepower running at efficiencies of more than 90 percent were generating electric power by the time of his death in 1910. The Pelton wheel is acclaimed as the only hydraulic turbine of the impulse type to use a large head and low flow of water in hydro-electric power stations. Pelton wheels are still in use today all over the world in hydroelectric power plants. The Pelton Wheel Company was so successful that it moved to larger facilities in San Francisco, in 1887.
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2.4 Advantages of Pelton Wheel:
Most efficient of all turbines
High overall efficiency
Simple in construction and easy maintenance
Easy assembly
Flat efficiency curve
Can be Operated at low discharge
Can be operated in silted water
2.5 Comparison with other turbines:
This turbine can strictly extract energy as of any fast-moving fluid, for example air, but almost always use water for utmost efficiency.
They can prepared out of metal, plastic, ceramic materials, while metal is generally preferred.
To derive more power, multiple jets (2 to 6) Pelton wheel may be used.
It makes them ideal for hydro-electric power generation.
Simple in construction and easy maintenance.
As Pelton turbine is not only turbines in existence, they are absolutely the mainly ideal impulse turbines while low flow rates or small streams are only sources of water accessible.
While they are ideal for location in which a stream of water has a high quantity of pressure by a low flow rate.
The quantity of energy to be extract as of small streams that would have or else gone to dissipate.
This is not the best turbines for low-pressure streams by a high flow rate.
A lot of head loss occurs when the river discharge is low.
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2.6 Uses of Pelton Wheel: Pelton wheels are the preferred turbine for hydro-power, when the available water source has relatively high hydraulic head at low flow rates, where the Pelton wheel is most efficient. Thus, more power can be extracted from a water source with high-pressure and low-flow than from a source with low-pressure and high-flow, even when the two flows theoretically contain the same power. Also a comparable amount of pipe material is required for each of the two sources, one requiring a long thin pipe, and the other a short wide pipe. Pelton wheels are made in all sizes. There exist multi-ton Pelton wheels mounted on vertical oil pad bearings in hydroelectric plants. The largest units can be up to 200 megawatts. The smallest Pelton wheels are only a few inches across, and can be used to tap power from mountain streams having flows of a few gallons per minute. Some of these systems use household plumbing fixtures for water delivery. These small units are recommended for use with 30 feet (9.1 m) or more of head, in order to generate significant power levels. Depending on water flow and design, Pelton wheels operate best with heads from 49–5,905 feet (14.9–1,799.8 m), although there is no theoretical limit.
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Chapter 3 Theory 3.1 Working principle of pelton wheel: The Pelton turbine is the most visually obvious example of an impulse machine. Nozzles direct forceful, high-speed streams of water against a rotary series of spoon-shaped buckets, also known as impulse blades, which are mounted around the circumferential rim of a drive wheel also called a runner. As the water jet impinges upon the contoured bucket-blades, the direction of water velocity is changed to follow the contours of the bucket. Water impulse energy exerts torque on the bucket-and-wheel system, spinning the wheel; the water stream itself does a "uturn" and exits at the outer sides of the bucket, decelerated to a low velocity. In the process, the water jet's momentum is transferred to the wheel and thence to a turbine. Thus, impulse energy does work on the turbine. For maximum power and efficiency, the wheel and turbine system is designed such that the water jet velocity is twice the velocity of the rotating buckets. A very small percentage of the water jet's original kinetic energy will remain in the water, which causes the bucket to be emptied at the same rate it is filled, and thereby allows the high-pressure input flow to continue uninterrupted and without waste of energy. Typically two buckets are mounted side-by-side on the wheel, which permits splitting the water jet into two equal streams. This balances the side-load forces on the wheel and helps to ensure smooth, efficient transfer of momentum of the fluid jet of water to the turbine wheel. Because water and most liquids are nearly incompressible, almost all of the available energy is extracted in the first stage of the hydraulic turbine. Therefore, Pelton wheels have only one turbine stage, unlike gas turbines that operate with compressible fluid. The operating characteristics of a turbine are often conveniently shown by plotting torque T, brake power Pb, and overall turbine efficiency ηt against turbine rotational speed n for a series of volume flow rates Qv,. It is important to note that the efficiency reaches a maximum and then falls, whilst the torque falls constantly and linearly. The optimum conditions for operation occur when the required duty point of head and flow coincides with a point of maximum efficiency. 15
Figure 3.1: Pelton wheel working procedure Pelton turbine is an impulse turbine. The runner of the Pelton turbine consists of double hemispherical cups fitted on its periphery. The jet strikes these cups at the central dividing edge of the front edge. The central dividing edge is also called as splitter. The water jet strikes edge of the splitter symmetrically and equally distributed into the two halves of hemispherical bucket. The inlet angle of the jet is therefore between 1° and 3º. Theoretically if the buckets are exactly hemispherical it would deflect the jet through 180°. Then the relative velocity of the jet leaving the bucket would be opposite in direction to the relative velocity of the jet entering. This cannot be achieved practically because the jet leaving the bucket then strikes the back of the succeeding bucket and hence overall efficiency would decrease. Therefore in practice the angular deflection of the jet in the bucket is limited to about 165° or 170°, and the bucket is slightly smaller than a hemisphere in size. The amount of water discharges from the nozzle is regulated by a needle valve provided inside the nozzle. One or more water jets can be provided with the Pelton turbine depending on the requirement.
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Let us consider that a jet of water issuing from the nozzle strikes the buckets of the runner of a Pelton wheel. Velocity diagram of Pelton wheel is given below:
Figure 3.2: Velocity diagram of Pelton wheel Here, V= absolute velocity of jet before striking the bucket V1= absolute velocity of jet leaving the bucket Vw= velocity of whirl at inlet Vw1= velocity of whirl at outlet v= peripheral velocity of the bucket at inlet v1= peripheral velocity of the bucket at outlet Vr= relative velocity of water and bucket at inlet Vr1= relative velocity of water and bucket at outlet Vf1= velocity of flow at outlet β = bucket tip angle at outlet with the tangent φ = blade vane angle 17
3.2 Working Proportions for Design of Pelton Wheel: I.
Velocity of jet: The theoretical velocity of the jet v1 2 gH
Where, H= net head. Actual Velocity of Jet va Cv 2 gH
Where, Cv is the co-efficient of velocity of the jet which varies from 0.98 to 0.99. II.
Power available to the turbine: P= γQH Where, γ is the specific weight of water, in N/m3, Q is the flow rate in m3/s and H is the head in meters.
III.
Diameter of the Jet (d): 18
The diameter of the jet is obtained if flow rate is known. For a single jet,
Q d 2va 4
Q d 2Cv 2 gH 4 4Q d C 2 gH v IV.
1
2
Speed ratio (φ): The speed ratio is the ratio of the velocity (u) of the wheel at pitch circle to theoretical velocity (v1) of the jet.
u uv 1 2 gH
In practice the value is between 0.44 and 0.46 and the average is 0.45.
V.
Mean Diameter of the wheel (D): It is the diameter between centers of the buckets. The diameter can be obtained from peripheral velocity (u).
u
DN
D
Or,
60 60u N
Where, N = speed of the wheel in revolutions/min. VI.
Jet ratio (m): The ratio of mean diameter of the wheel to diameter of the jet. 19
m
D d
The Jet ratio varies from 10 to 14 and average value of m is 12.
VII.
Size of the buckets: The length, width and depth of buckets in terms of diameter of jet ‘d’ is shown in figure
Figure 3.3: Dimensions of Bucket.
VIII.
Radial length of bucket
L= 2 to 3d
Axial width of bucket
B= 3 to 5d
Depth of bucket
D= 0.8 to 1.2d
Number of buckets (z):
20
The number of buckets is usually obtained from the following empirical formula given by Taygun.
zD
2d
15 0.5m 15
Where, m is the jet ratio.
IX.
Specific speed (Ns): The specific speed value (radian/second) for a turbine is the speed of a geometrically similar turbine which would produce one unit of the specific speed of a turbine is given by the manufacturer (along with other ratings) and will always refer to the point of maximum efficiency. This allows accurate calculations to be made of the turbine's performance for a range of heads. For Pelton wheel specific speed (Ns) typically around 4.
Ns
N P H
Where, N=rpm
21
5
4
3.3 Pelton turbine losses and efficiencies: Head losses occur in the pipelines conveying the water to the nozzle due to friction and bend. Losses also occur in the nozzle and are expressed by the velocity coefficient, Cv. The jet efficiency (ηj) takes care of losses in the nozzle and the mechanical efficiency (ηm) is meant for the bearing friction and windage losses. The overall efficiency (ηo) for large Pelton turbine is about 85– 90%. Following efficiency is usually used for Pelton wheel. Pipeline transmiss ion efficiency
Energy at end of the pipe Energy available at reservoir
Figure 3.4 shows the total headline, where the water supplies from a reservoir at a head H1 above the nozzle. The frictional head loss, hf, is the loss as the water flows through the pressure tunnel and penstock up to entry to the nozzle. Then the transmission efficiency is trans ( H 1 h f ) H 1 H H 1
The nozzle efficiency or jet efficiency is
j
Energy at nozzle outlet v a2 2 gH Energy at nozzle inlet
Figure 3.4: Schematic layout of hydro plant 22
Nozzle velocity coefficient, Cv
Actual jet veloci ty va Theoretica l jet veloci ty
2 gH
Therefore the nozzle efficiency becomes
j va2 2 gH Cv2 The characteristics of an impulse turbine are shown in Fig. 3.5 and Fig 3.6 Figure 3.5 shows the curves for constant head and indicates that the peak efficiency occurs at about the same speed ratio for any gate opening and that the peak values of efficiency do not vary much. This happens as the nozzle velocity remaining constant in magnitude and direction as the flow rate changes, gives an optimum value of U/C1 at a fixed speed. Due to losses, such as windage, mechanical, and friction cause the small variation. Fig. 3.6 shows the curves for power vs. speed. Fixed speed condition is important because generators are usually run at constant speed.
Figure 3.5: Efficiency vs. speed at various nozzle settings. 23
Figure 3.6: Power vs. speed of various nozzle setting.
Figure 3.7: Pelton turbine losses and efficiencies The hydraulic losses in penstock is hf , head loss in nozzle is hn. The head before the turbine inlet is H and hydraulic power input is γQH. There are l osses like eddies and leakage in the turbine. Head available at the runner is E. There are mechanical losses and as a result shaft power is P. There are transmission and generator losses and net electrical power generated by generator PE.
H = H1 - (h f + h n ) 24
CHAPTER 4 EXPERIMENTAL SETUP 4.1 Full setup: Different parts were designed and assembled in solidworks with proper dimensions.
Figure 4.1: Front View of upper portion of the Setup
Figure 4.2: Back View of upper portion of the setup
25
Figure 4.3: Showing the torque measurement arrangement of the setup and nozzle position.
Figure 4.4: Isometric view of full setup
26
4.2 Design: 4.2.1 Bucket: Bucket was made of Aluminum. The length of the bucket is, Lb=2.5 inch, width, Bb=4 inch and depth, Db= 1 inch. The length of the handle of the bucket is 2 inch and the gap between two handles is 1 inch.
Figure 4.5: Bucket
4.2.2 Rim: The outer diameter is 9.5 inch and is has 12 buckets with equal division. Diameter for shaft hole is 1.5 inch. The angle between two buckets is 30o. The rim is made of stainless steel sheet metal. The thickness of the rim is 1 inch.
Figure 4.6: Rim
27
4.2.3 Shaft: Length of the shaft is 18 inch and diameter of the shaft is 1.5 inch. Material: stainless steel.
Figure 4.7: Shaft
4.2.4 Wheel Casing: Wheel casing is made of 2 mm Stainless steel sheet metal. It has two holes. One is for shaft and the other is for nozzle. Length of the casing is 24.5 inch, width is 15 inch and height is 25.5 inch. Nozzle hole is 7.25 inch and shaft hole is 13.25 inch above from bottom. Casing has a slot at bottom for water disposal of 20 inch long and 11 inch wide. The view from different angle is given below.
Figure 4.8: Front View of Casing 28
Figure 4.9: Orthographic View of casing
The Solidworks view of casing describes the proper alignment of casing.
Figure 4.10: Solidworks view of casing
29
4.2.5 Brake Drum: Brake drum is of around 8 inch in diameter and for shaft alignment it got a 1.5 inch diameter hole at the center. It has also a slot for belt alignment of 0.5 inch.
Figure 4.11: Solidworks view of Brake drum
4.2.6 Supporting Table: The supporting table is 3.84 ft long, 3.16 ft wide and 3 ft in height. The frame of the table was made of stainless steel hollow rectangular bar. The top part of the table is covered with 1 mm stainless steel sheet metal. There is a slot of 20 inch long and 11 inch wide on top of the supporting table. Above all, it has supporting for disposal bucket of 1.5 ft higher from the ground. It has also 6 caster wheels for easy movement of the setup.
Figure 4.12: Solidworks view of supporting table
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4.2.7 Disposal bucket: The length of the disposal bucket is 3.7 ft, width is 3 ft and height is 2 ft. It has a hole of 2 inch diameter near bottom for drain of water. The disposal bucket is also made with thickness of 1 mm stainless steel sheet metal.
Figure 4.13: Solidworks view of disposal bucket
Figure 4.14: Full view of the setup 31
4.3 Equipments: 4.3.1 Pressure Gauge: Pressure gauge was attached with pipeline before nozzle to measure the pressure. It is one of the most important equipment of this setup.
Figure 4.14: Pressure gauge
Specification: Range: (0~60) psi and (0~4) kgf/cm2 Working Pressure: Steady: 3/4 of full scale value (recommendation 25% to 75% of full scale) Fluctuating: 2/3 of full scale value (recommendation lower 50% of full scale) Short time: full scale value Operating Temperature: Ambient: -20 ~ 65°C Media (Fluid): -5 ~ 40°C
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4.3.2 Water Meter: A water meter is also attached with the pipeline after pressure gauge to measure the flow. The flow rate, Q can be measured by it with the help of stopwatch.
Figure 4.15: Flow Meter Specification: Technical data conform to international Standard ISO4064 Class B Working condition:
a) Water temperature 0.1℃～40℃ b) Water pressure ≤1.0MPa
Maximum permissible error: a) In the lower zone from qmin inclusive up to but excluding qt is ±5% b) In the upper zone from qt inclusive up to and including qs is ±2%
Figure 4.16: Flow error curve
33
4.3.3 Tachometer: A tachometer was used to measure the RPM of the wheel.
Figure 4.17: Digital Tachometer Specification: Photoelectric rotation speed: 2.5~99999RPM(r/min) Contact rotation speed: 0.5~19,999RPM(r/min) Basic Accuracy: ± (0.05%+1digit) Effective distance: 50mm~250mm Maximum display: 99999
4.3.4 Stop watch: To calculate flow rate, Q stopwatch is used to measure elapsed time for certain amount of flow. Its accuracy is 30 Laps and Split Memory at 1/100 sec.
Figure 4.18: Stop watch 34
4.3.5 Spring Balance: A spring balance was used to measure the applied load on the brake drum.
Figure 4.19: Spring Balance Specification: Range: 25kg/56lb Material: Copper Measure Method: Manual
35
4.4 Construction: 4.4.1 Construction of penstock: The penstock was configured by GI pipe. The total length of the penstock is around 110 ft. The diameter of pipe is 1.5 inch. The penstock was constructed by the help of plumber. The water reservoir is on top of the 10th floor. Different types of fittings were used while penstock established. Some of them are named union, nipple, elbow, T-joint, reducer etc.
Figure 4.20: GI pipe
Figure 4.21: Different types of fittings
36
Figure 4.22: Penstock
4.4.2 Nozzle: The nozzle is made of brass. External thread diameter is 1 inch and nozzle diameter is 0.45 inch
Figure 4.23: Nozzle
37
Figure 4.24: Nozzle arrangement
4.4.3 Runner: It has two parts, rim and bucket. The outer diameter of rim is 9.5 inch and it can accommodate 12 buckets with equal divisions. Diameter for shaft hole on the rim is 1.5 inch. The angle between two buckets is 300. The rim is made of 2 mm thick stainless steel sheet metal. Later two circular portions were TIG welded to join together. The thickness of the rim is 1 inch. Buckets were made of Aluminum. Using the oldest method, at first bucket pattern was made according to the design and then sand cast aluminum bucket produced. The length of the bucket is, Lb=2.5 inch, width, Bb=4 inch and depth, Db= 1 inch. The length of the handle of the bucket is 2 inch and the gap between two handle is 1 inch. Then Buckets were drilled with desired dimensions and later bolted on the rim maintaining equal angle of 300.
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Figure 4.25: Bucket
Figure 4.26: Runner assembly 39
4.4.4 Wheel casing: Wheel casing is made of 2 mm Stainless steel sheet metal. It has two holes. One is for shaft and the other is for nozzle. Length of the casing is 24.5 inch, width is 15 inch and height is 25.5 inch. Nozzle hole is 7.25 inch and shaft hole is 13.25 inch above from bottom. Casing has a slot at bottom for water disposal of 20 inch long and 11 inch wide. The different parts were joined by TIG (Tungsten Inert Gas) Welding process to obtain better finishing and strength. Desired holes were created by drilling. At last hand grinder was used to finish the weld surface. Then the front part of the casing was covered with 8 mm thick Acrylic sheet for better view of the wheel. After that, silicon adhesive was used between acrylic and casing to avoid water leakage.
Figure 4.27: construction of casing
40
4.4.5 Torque measurement arrangement: The most important part of torque measurement arrangement is the brake drum. The material of the brake drum is nylon. It is of around 8 inch in diameter and for shaft alignment it got a 1.5 inch diameter hole at the center. It has also a slot for belt alignment of 0.5 inch. The length of the belt is around 70 cm. To accommodate the brake drum a support was made using stainless steel hollow rectangular bar and pillow bearing. On top of the support bar, two long bolts were welded and two hooks were attached with the bolt to serve the spring balance. Two spring balance were used to measure the applied load on the brake drum. A belt was used to connect the spring balance with brake drum.
Figure 4.28: Torque measurement arrangement
41
4.4.6 Supporting table: The supporting table is 3.84 ft long, 3.16 ft wide and 3.25 ft in height. The frame of the table was made of stainless steel hollow rectangular bar. The top part of the table is covered with 1 mm stainless steel sheet metal. There is a slot of 20 inch long and 11 inch wide on top of the supporting table. Above all, it has supporting for disposal bucket of 1.25 ft higher from the ground. It has also 6 caster wheels for easy movement of the setup. Above all, it accommodates the wheel casing, runner, shaft, torque measurement arrangement and also disposal bucket.
Figure 4.29: Supporting table frame
4.4.7 Water disposal: It consists of disposal bucket and water drainage network. The length of the disposal bucket is 3.7 ft, width is 3 ft and height is 1.9 ft. It has a hole of 2 inch diameter near bottom for drainage of water. The disposal bucket is also made with thickness of 1 mm stainless steel sheet metal. To drain the water of the setup, 50 ft long uPVC (unplasticized polyvinyl chloride) pipe were used. To finish the connection, some fittings and adhesive solution were also needed. By the help of plumber the whole disposal connection were accomplished. So, the disposal water can be drained to the underground reserve tank.
42
Figure 4.30: Disposal bucket
Figure 4.31: Disposal route equipments
Figure 4.32: Disposal pipeline
43
CHAPTER 5 EXPERIMENTAL DATA COLLECTION & CALCULATION 5.1 Experimental procedures: Gate valve of the main pipe line was opened at the very beginning of the experiment. Then the belt of torque measurement arrangement with no tension was set. After that 2 lb load applied to brake drum with the help of nut bolt which is attach with the frame. After setting the load, ball valve was opened. As a result jet struck the buckets. For that runner began to rotate as well as the brake drum. Pressure was set 10 psi to start the main procedure. Amount of flow water was taken from flow meter. To calculate flow rate, Q, time was counted using stopwatch. Tachometer was subjected to the shaft to find the speed, N of the wheel in rpm. Meanwhile the reading from spring balance was taken. The same experiment for different pressure (12psi-30psi) was repeated. When the experiment was over, the load was removed from the brake drum and all the valves closed which were provided for controlling the jet speed.
44
5.2 Data Table:
No. of obs.
Time (s)
01.
Radius of the brake drum = 0.09 m
Volume (m3)
Flow rate, Pressure, Q P (m3/s) (psi)
Pressure, P (Pa)
Speed, N (rpm)
T1 (lb)
T2 (lb)
(T1-T2) (kg)
2
Load for braking torque, (T1-T2) (lb) 3
113
8.85×10-4
10
68.94×103
190
5
02.
111
9×10-4
12
82.73×103
210
5.25
2
3.25
1.47
03.
97
1.03×10-3
14
96.52×103
240
5.5
2
3.5
04.
93
1.07×10-3
16
110.31×103
235
6
2
4
1.81
05.
91
1.09×10-3
18
124.1×103
247
6.15
2
4.15
1.88
06.
88
1.13×10-3
20
137.89×103
250
6.5
2
4.5
2.04
07.
83
1.2×10-3
22
151.68×103
310
7
2
5
2.26
08.
71
1.4×10-3
24
165.47×103
315
7.2
2
5.2
2.35
09.
65
1.54×10-3
26
179.2×103
340
7.5
2
5.5
2.49
10.
60
1.66×10-3
28
193.05×103
410
7.8
2
5.8
2.63
11.
55
1.82×10-3
30
206.84×103
430
8.2
2
6.2
2.81
0.1
45
1.36
1.59
5.3 Calculation: 5.3.1 Sample calculation: For observation no. 1:
Head, H =
=
P 68.94 103 9810
=7.02 m
Input power, Pi = QH =9810×(8.85×10-4) ×7.02 =60.94 Watt
Output power, Po = T1 T2 g =1.36×9.81×
2N R 60 2 3.1416 190 ×0.09 60
=23.77 Watt
Efficiency, = =
Po Pi 23.77 60.94
=39%
46
Velocity, va = =
Q A
4
Q d2
Here, d = diameter of jet =0.45 inch =0.01143 m va =
=
4Q d2
4 (8.85 104 ) 3.1416 (0.01143)2
=8.625 ms-1
Coefficient of velocity, Cv = =
va 2 gH 8.625 2 9.81 7.02
=0.73
Peripheral speed of the wheel, u =
DN 60
Here, D = mean diameter of the wheel =12 inch =0.3048 m u
=
3.1416 0.3048 190 =3.04 ms-1 60
47
Speed ratio, = =
u va 3.04 8.625
= 0.35
Specific speed, N s =
N Po H
=
5
[where, Po is in kW]
4
190 23.77 103 (7.02)
5
4
= 2.56 rpm
48
CHAPTER 6 RESULT & DISCUSSION 6.1 Calculation Table:
No. of Obs.
H (m)
Q (m3/s)
va (ms-1)
Cv
Pi (W)
Po (W)
Speed ratio, φ
Efficiency, η(%)
Torque, T (N.m)
39%
Specific speed, Ns (rpm) 2.56
01.
7.02
8.85×10-4
8.625
0.73
60.94
23.77
0.35
02.
8.43
9×10-4
8.771
0.68
74.42
28.4
0.38
38.16%
2.46
1.29
03.
9.83
1.03×10-3
10.03
0.72
99.32
35.10
0.38
35.34%
2.58
1.4
04.
11.24
1.07×10-3
10.42
0.70
117.98
39.13
0.36
33.16%
2.26
1.6
05.
12.65
1.09×10-3
10.62
0.67
135.26
42.72
0.37
31.64%
2.13
1.65
06.
14.05
1.13×10-3
11.01
0.66
155.74
46.92
0.36
30.12%
1.99
1.8
07.
15.46
1.2×10-3
11.69
0.67
181.99
64.45
0.42
35.41%
2.56
1.98
08.
16.86
1.4×10-3
13.64
0.75
231.55
68.10
0.36
29.41%
2.4
2.06
09
18.26
1.54×10-3
15
0.79
275.86
77.88
0.36
28.23%
2.51
2.19
10.
19.67
1.66×10-3
16.17
0.82
320.31
99.2
0.4
30.96%
3.12
2.31
11.
21.08
1.82×10-3
17.73
0.87
376.36
111.2
0.38
29.53%
3.17
2.47
Results: Mean coefficient of velocity of the nozzle, Cv = 0.73 Mean speed ratio, φ = 0.37 Mean specific speed, Ns = 2.52 Mean efficiency of the wheel, η = 32.81%
49
1.19
6.2 Graphs & Discussion: Following performance characteristics curves will be discussed:
Head vs. Flow rate
Speed vs. Flow rate
Torque vs. Flow rate
Output power vs. Flow rate
Output power vs. Input power
6.2.1 Head vs. Flow rate:
Figure 6.1: Head vs. Flow rate curve
From the graph of head against flow rate; head increases from 7.2 m to 21.08 m and the volumetric flow rate was increasing from 8.85×10-4 m3/s to 1.82×10-34 m3/s. As the head of water increases the pressure is increased. This increase in pressure influences the power delivered to the wheel by the jet of water. The curve fluctuated at some point. Due to frictional loss and some leakage of pipe line it occurred.
50
6.2.2 Speed vs. Flow rate:
Figure 6.2: Speed vs. Flow Rate curve
This graph shows the relationship between speed and flow rate from the nozzle. As the speed increases from 190 rpm to 430 rpm, the volumetric flow rate increases from 8.85×10-4 m3/s to 1.82×10-34 m3/s. So the head of water increases with the increase of speed. As the speed is correlated with head so with the increase of head, speed of wheel also increases. Fluctuation takes place at some point. Digital tachometer’s instability is the hindrance of it. Again frictional loss of pipe line and some leakage losses are also responsible for it.
51
6.2.3 Torque vs. Flow rate:
Figure 6.3: Torque vs. Flow rate curve
This graph shows the relationship between torque and flow rate from the nozzle. As the torque increases from 3 lb to 6.2 lb, the volumetric flow rate increases from 8.85×10-4 m3/s to 1.82×1034
m3/s. So the torque increases with the increase of speed. Increase of speed results the increase
of applied load to the brake drum. As torque is interrelated with load so with the increase of load, torque increases gradually. Digital tachometer’s instability is the main reason of the seesaw of the curve.
52
6.2.4 Output power vs. Flow rate:
Figure 6.4: Output power vs. Flow rate curve
From the graph of output power against flow rate from the nozzle, as the flow rate increases from 8.85×10-4 m3/s to 1.82×10-34 m3/s output power increases from 23.77 watt to 111.16 watt. As the flow rate of water increases the load is also increased. Flow rate is the reason for increasing the speed of the wheel. And the load of the brake drum is related with torque. So increase of speed and torque results the increase of output power. Head loss, leakage and tachometer instability is the reason for the fluctuation.
53
6.2.5 Output power vs. Input power curve:
Figure 6.1: Output power vs. Input power
This graph shows the relationship between output power and input power. In this graph best fitted line is used which maintains the straight line equation y=mx. Frictional loss, leakage loss, inaccuracy in measurement, visual errors while taking data, large fraction inaccuracy, digital tachometer instability etc. are the main reasons behind it. From this graph, slope, m=0.276. So, efficiency determined from the curve is, η= 27.6%.
54
The main objective of this experiment is to construct Pelton Turbine with proper design and accuracy as close as possible compared to ideal Pelton Turbine and to measure the performance characteristics values using experimental procedure. And also to find the performance characteristics curve. The whole construction was done with great keenness and persistence. According to design equation, the runner should have 21 buckets but as the main concern of the thesis was only to demonstrate Pelton wheel for study purpose, 12 buckets were put in work. The Jet ratio varies from 10 to 14 but for the same reason it was also overlooked. These are some crucial points of deviation from standard values. From result, coefficient of velocity, Cv, is 0.73. But in ideal condition it must be from 0.98 to 0.99. The reason of this error is sudden contraction of nozzle. For lack of spacing in casing a short length of nozzle is used but the jet diameter remains same. So for this sudden contraction coefficient of velocity is formed to be lower than the ideal one. For some losses the values of specific speed, speed ratio differs from ideal values. Frictional loss, inaccuracy in measurement, visual errors while taking data, round off error, leakage losses, digital tachometer instability etc. are the main reasons behind it. From the results, it is shown how Pelton Wheel reacts to different kinds of input. Different flow rates give different values of work input. The slower the flow rates, the larger the work being put into the wheel. The efficiency of the slower flow rates is also better than faster one. The speed of the wheel is also dropped when much weight is being applied until it stopped suddenly when the weight is too much for it to go against.
55
CHAPTER 7 CONCLUSION The experiment of the thesis was carried out with an acceptable level of accuracy. It was generally a success as the results obtained were useful for the analysis of the properties of the machine. From the experimental results, it became possible for the real picture of the operational basis of the machine to be displayed in such a way that the characteristics of the turbine were visible in the graphical analysis used. The experiment was not fully accurate due to several errors that resulted from several misdoings. The greatest being that it became really difficult to acquire readings from the spring balance since the setup was vibrating as result of the operation of the machine. As such, this explains the slight deviation of the results obtained in the experiment that were later reflected in the graphs drawn to represent the work. Other errors may have resulted from unseen leakages in the system and observational and computational errors. The experiment was, however, carried out with a great level of keenness to reduce the occurrence of such errors. Some of the limitations are represented below:
Pressure must not exceed 30psi as it can be destructive for the buckets.
Initial load at the brake drum must be low for the same reason.
Vast amount of water gets wasted due to absence of recycling system design.
Due to excess rotation of the brake drum too much heat is generated which causes the belt to cling with the brake drum.
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There is a huge field of research in this sector for further improvement. The further recommendations are as follows:
A DC Motor can be coupled with the shaft to generate electricity. But this power will be very small.
Bucket material may be changed. Different materials, such as stainless steel, carbon steel, composites or melamine can be used which may improve the efficiency of the pelton turbine.
The disposal water can be recycled.
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REFERENCES 1. Yassi, Y. (1999) An experimental study of improvement of a micro hydro turbine performance. University of Glasgow. 2. Thermo fluid Lab manual, University TenagaNasional. 3. http://en.wikipedia.org/wiki/Pelton_wheel 4. http://www.green-mechanic.com/2014/06/pelton-wheel-turbine.html 5. http://4mechtech.blogspot.com/2014/06/Advantages-and-Disadvantages-of-ImpulseTurbine.html 6. http://www.oldpelton.net/history/ 7. https://www.scribd.com/doc/138061490/Pelton-Turbine-Report#scribd 8. http://www.wika.us/products_PM_en_us.WIKA 9. http://www.hiscoi.com/eng/product/product_main.html?parent=1 10. http://fetweb.ju.edu.jo/staff/me/jyamin/Turbomachine%20Textbook/dke672_ch3.pdf 11. http://www.learnengineering.org/2013/08/pelton-turbine-wheel-hydraulic-turbine.html 12. http://www.ijens.org/1929091%20ijet.pdf 13. http://www.lselectric.com/how-a-pelton-wheel-works/
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