Impulse Turbine

12 Key excerpts on "Impulse Turbine"

• 

  eBook - PDF

  Reeds Vol 3: Applied Thermodynamics for Marine Engineers

  • Paul Anthony Russell, William Embleton, Leslie Jackson(Authors)
  • 2022(Publication Date)
  • Reeds

    (Publisher)

  A turbine is a machine for converting the heat energy in the working fluid (gas or steam) into mechanical energy at the output shaft. This series of events is reversed in the rotary compressor as the input drive gives increased velocity to the fluid in the blades which is converted to pressure rise in a fixed diffuser ring. In the axial-flow turbine the rotor coupled to the shaft receives its rotary motion direct from the action of a high velocity jet impinging on blades fitted into grooves around the periphery of the rotor. There are two types of turbine, the impulse and the ‘reaction’. In both cases the fluid is allowed to expand from a high pressure to a lower pressure so that it acquires a high velocity at the expense of pressure, and this high velocity fluid is directed on to curved section blades which absorb some of its velocity; the difference is in the methods of expanding the working fluid. In Impulse Turbines the fluid is expanded in nozzles in which the high velocity of the fluid is attained before it enters the blades on the turbine rotor, and the pressure drop and consequent increase in velocity therefore takes place in these nozzles. As the fluid passes over the rotor blades it loses velocity but there is no fall in pressure. In ‘reaction’ turbines, expansion of the fluid takes place as it passes through the moving blades on the rotor as well as through the guide blades fixed to the casing. For a 50% reaction design (usual) the pressure (and enthalpy) ratios across fixed and moving blades are approximately equal. The Impulse Turbine As stated above, in the Impulse Turbine the high pressure fluid passes into nozzles wherein it expands from a high pressure to a lower pressure and thus the heat energy is converted into velocity energy (kinetic energy). The high velocity jet is directed on TURBINES 12

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Turbomachinery

  Concepts, Applications, and Design

  • V. Dakshina Murty(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  Hydraulic turbines are classified broadly into impulse and reaction turbines. Pelton wheel is the most common form of impulse type turbine while Francis turbine and Kaplan turbine are reaction type. A guide to the selection of turbines based on the head and power requirement is shown in Figure 4.2. Pelton wheels are most suitable for high heads and low flow rates. Kaplan turbines (somewhat the reverse of an exhaust fan!) are suited to high flows and low heads. This is related to the specific speeds, as discussed in Chapter 2, wherein it was shown that higher heads and lower flows give rise to lower specific speeds (Impulse Turbines) and lower heads with higher flows imply higher specific speeds (reaction turbines). A detailed discussion on turbine selection, plant capacity determination, and economic and hydrologic analysis can be found in Warnick et al. (1984).

  FIGURE 4.2 Guide to selecting hydraulic turbines. (From Walters, R. N. and Bates, C. G., (1976) Selecting Hydraulic Reaction Turbines, Engineering Monograph No. 20, Bureau of Reclamation, U.S. Department of the Interior, Washington, D.C.)

    4.2 Impulse Turbines

  An Impulse Turbine (in the context of hadraulic turbines) is one in which the total pressure drop of the fluid occurs inside one or more nozzles and there is no drop in pressure as the fluid flows through the rotor. Such turbines are most useful when water is available at very high heads, that is, with large potential energy. When such large heads are available, the potential energy is first converted into kinetic energy by letting the fluid flow through large pipes called penstock , and the high kinetic energy fluid then impinges on vanes or buckets. Thus, kinetic energy is converged into force, which results in torque on the shaft. A small part of the kinetic energy is lost in fluid friction on the wheels, and another small part is lost as kinetic energy of the fluid leaving the vanes.

  4.2.1 Pelton Wheel

  A hydraulic Impulse Turbine is called a Pelton wheel , which is by far the most important machine among the hydraulic turbines. It has evolved from the development of the earliest hydraulic turbines, frequently called waterwheels . It is named after Lester A. Pelton (1829–1908), who patented it in 1890.

  The locations of some Pelton turbine installations are shown in Table 4.1. A brief perusal of the table shows that the range of specific speeds is well within the accepted limits for Impulse Turbines indicated in Table 2.2.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Energy Conversion

  • D. Yogi Goswami, Frank Kreith, D. Yogi Goswami, Frank Kreith(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  12    

  Hydraulic Turbines

    Roger E.A. Arndt and Leonardo P. Chamorro CONTENTS 12.1   General Description 12.1.1   Typical Hydropower Installation 12.1.2   Turbine Classification 12.1.2.1   Impulse Turbines 12.1.2.2   Reaction Turbines 12.2   Principles of Operation 12.2.1   Power Available and Efficiency 12.2.2   Similitude and Scaling Formulae 12.3   Factors Involved in Selecting a Turbine 12.3.1   Performance Characteristics 12.3.1.1   Impulse Turbines 12.3.1.2   Reaction Turbines 12.3.1.3   Performance Comparison 12.3.2   Speed Regulation 12.3.3   Cavitation and Turbine Setting 12.4   Performance Evaluation 12.4.1   Model Tests 12.5   Numerical Simulations 12.6   Field Tests 12.7   Other Concepts: Hydrokinetic Turbines Defining Terms References Further Information

  A hydraulic turbine is a mechanical device that converts the potential energy associated with a difference in water elevation (head ) into mechanical work. Modern hydraulic turbines are the result of many years of gradual development. Economic incentives have resulted in the development of very large units (exceeding 800 MW in capacity, i.e., two orders of magnitude larger than their wind counterparts) with efficiencies that are sometimes in excess of 95%.

  However, the emphasis on the design and manufacture of very large turbines has shifted to the production of smaller units, especially in developed nations, where much of the potential for developing large base-load plants has been realized. At the same time, the sustained increase in the cost of energy has made many smaller sites economically feasible and has greatly expanded the market for smaller turbines. The increased value of energy also justifies the cost of refurbishment and increasing the capacity of older facilities with modern runners having higher efficiency and greater capacity. The introduction of high-performance computational tools in the last decade has had considerable influence on the design of hydraulic systems, their operation, and control.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Mechanical Design and Manufacture of Hydraulic Machinery

  • Mei Zu-yan(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  Chapter 5

  Construction of Impulse Turbines

  G. Borciani

  5.1 General

  The Impulse Turbine has a basic feature, in that all the available energy in the water is fully converted in the distributor system into kinetic energy which is transferred to the runner according to the impulse principle. This is the first difference between impulse and reaction turbines, the second is that the impulse (or action) turbine has a partial water admission, that is water impinges on the runner at one or several points on the periphery only (see Volume Hydraulic Design of Hydraulic Machinery of this Book Series.

  Small turbines, like the inclined jet turbine and the cross–flow turbines, are usually classified as Impulse Turbines although they have some degree of reaction. These turbines will be described in detail in Chapter 10 .

  The most important Impulse Turbine is the Pelton turbine, named after L. A. Pelton who in 1880 invented the central ridge (splitter) for the buckets. Around 1900, A. Dohle used a double–elliptic shape bucket and a needle for the control of discharge for the first time.

  Most Pelton turbines built up to 1960 are of the horizontal type. Only after the wider application of the vertical design did the power of Pelton turbines exceed the 100MW mark, see Figure 5.1 . The two units at the Sy–sima plant (Norway, 1981) each with five jets are rated at 315MW at n = 5s −1 (300rpm) under a specific hydraulic energy 1 E of 8690· kg −1 (H = 885m ). The three Pelton turbines at Reisseck (Austria, 1970) operate under the highest value of E in the world of 17318 J · kg −1 (H = 1765m ).

  The operating scheme of a Pelton turbine is fairly simple, as shown by the horizontal two–jet machine in Figure 5.2 . Water from the penstock 1 passes through the spherical valve 2 which has a two–fold task: to permit inspection and maintenance of the turbine, and stopping the machine in an emergency, for example the failure of the normal closing system. The feeding system (distributor) consists of the two branches 4 connecting the spherical valve to the two nozzles 5 through which the energy of the water is transformed into kinetic energy in the form of a free jet. The jet impinges on a series of buckets 6 set at the periphery of the runner and causes it to rotate. In the diagram, D is the jet circle diameter and d 0

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Turbomachinery

  Design and Theory

  • Rama S.R. Gorla, Aijaz A. Khan(Authors)
  • 2003(Publication Date)
  • CRC Press

    (Publisher)

  3 Hydraulic Turbines 3.1 INTRODUCTION In a hydraulic turbine, water is used as the source of energy. Water or hydraulic turbines convert kinetic and potential energies of the water into mechanical power. The main types of turbines are (1) impulse and (2) reaction turbines. The predominant type of impulse machine is the Pelton wheel, which is suitable for a range of heads of about 150−2,000 m. The reaction turbine is further subdivided into the Francis type, which is characterized by a radial flow impeller, and the Kaplan or propeller type, which is an axial-flow machine. In the sections that follow, each type of hydraulic turbine will be studied separately in terms of the velocity triangles, efficiencies, reaction, and method of operation. 3.2 PELTON WHEEL An American Engineer Lester A.Pelton discovered this (Fig. 3.1) turbine in 1880. It operates under very high heads (up to 1800 m.) and requires comparatively less quantity of water. It is a pure Impulse Turbine in which a jet of fluid delivered is by the nozzle at a high velocity on the buckets. These buckets are fixed on the periphery of a circular wheel (also known as runner), which is generally mounted on a horizontal shaft. The primary feature of the impulse Figure 3.1 Single-jet, horizontal shaft Pelton turbine. turbine with respect to fluid mechanics is the power production as the jet is deflected by the moving vane(s). The impact of water on the buckets causes the runner to rotate and thus develops mechanical energy. The buckets deflect the jet through an angle of about 160 and 165° in the same plane as the jet. After doing work on the buckets water is discharged in the tailrace, and the whole energy transfer from nozzle outlet to tailrace takes place at constant pressure. The buckets are so shaped that water enters tangentially in the middle and discharges backward and flows again tangentially in both the directions to avoid thrust on the wheel.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Fox and McDonald's Introduction to Fluid Mechanics

  • Robert W. Fox, Alan T. McDonald, John W. Mitchell(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  Performance Characteristics for Hydraulic Turbines The Impulse Turbine is a relatively simple turbomachine and used to illustrate typical test results. Most Impulse Turbines used today are improved versions of the Pelton wheel developed in the 1880s by Amer- ican mining engineer Lester Pelton. An Impulse Turbine is supplied with water under high head through a long conduit called a penstock. The water is accelerated through a nozzle and discharges as a high-speed free jet at atmospheric pressure. The jet strikes deflecting buckets attached to the rim of a rotating wheel, reducing the jet kinetic energy. Turbine output is controlled by changing the flow rate of water striking the buckets. Water discharged from the wheel at relatively low speed falls into the tailrace. Figure 10.29 illustrates an impulse-turbine installation. The gross head available is the difference between the levels in the supply reservoir and the tailrace. The effective or net head, H, used to calculate efficiency, is the total head at the entrance to the nozzle measured at the nozzle centerline [7]. Not all of the net head is converted into work at the turbine as some is lost to turbine inefficiency, some in the nozzle itself, and some as residual kinetic energy in the exit flow. The penstock usually is sized so that the net head is 85–95 percent of the gross head. Figure 10.30 shows typical results from tests performed at constant head. Setting up the velocity triangle: β 2 = tan − 1 V t 2 − U 2 V n 2 = tan − 1 125 4 − 115 35 = 16 58 β 2 α 2 = tan − 1 V t2 V n2 = tan − 1 125 4 10 5 = 85 2 α 2 (c) To calculate the efficiency: η t = W m W h = gH T gH E = 448 500 = 89 6 η This problem demonstrates the analysis of a hydraulic turbine with head losses and quantifies those effects in terms of a turbine efficiency. In addition, since the head at the turbine exit is below atmospheric, care must be taken to ensure that cavitation does not occur.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Process Plant Machinery

  • Heinz P. Bloch, Claire Soares(Authors)
  • 1998(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Steam Turbines 137 IMPULSE STEAM TURBINES The Impulse Turbine has little or no pressure drop across its moving blades. Steam energy is transferred to the rotor entirely by the steam jets striking the moving blades (Figure 5-1). Since there is theoretically no pressure drop across the moving blades (and thus no reaction), internal clearances are large and no balance piston is needed. These features make the Impulse Turbine a rugged and durable machine that can withstand the heavy-duty service of today's mechanical drive applications. Steam turbine materials are tabulated in Table 5.2. Velocity-Compounded (Curtis) Staging A Curtis stage (Figure 5-2) consists of two rows of moving blades. Stationary nozzles direct the steam against the first row; reversing blades (not nozzles) then redirect it to the second row. The large pressure drop through the nozzle produces a high-speed steam jet. This high velocity is absorbed in a series of constant pressure steps (see below). The two rotating rows of blades make effective use of the high-speed jet, resulting in small wheel diameters and tip speeds, fewer stages, and a shorter, more rugged turbine for a given rating. Pressure-Compounded (Rateau) Staging Again referring to Figure 5-2, we observe how in Rateau staging the steam path is slightly different. Here the heat energy of the steam is converted into work by stationary nozzles (diaphragms) directing the steam against a single row of moving blades. As in a Curtis stage, pressure drops occur almost entirely across the stationary nozzles. Turbine Configuration Overview Single-flow condensing units (Figure 5-3) require less steam for a given horsepower than other types. They expand steam from inlet pressure to a pressure less than atmospheric. The exhaust pressure is maintained by a condenser, providing for recovery of the spent steam. A condensing unit thus minimizes the need for makeup water.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Power Plant Engineering

  • Farshid Zabihian(Author)
  • 2021(Publication Date)
  • CRC Press

    (Publisher)

  reaction force , such as the force created when a balloon full of air is released to deflate and as a result, it spirals in air. We will start our discussion with Impulse Turbines.

  6.2     Impulse Turbines

  When two objects collide, they impose forces on each other called the impact force. Impulse blades operate based on the same concept. In these blades, the flow of the working fluid impinges the blades of the turbine. The blades, in turn, alter the direction of the flow. This results in the change in the momentum of the flow (Reminder Box 6.1 ). According to the second law of Newton (

  F d t = m d V

  ), this will create impulse force. In other words, in Impulse Turbines, the kinetic energy of the stream is converted to the shaft work .

  REMINDER BOX 6.1 LINEAR MOMENTUM CONSERVATION

  From fluid mechanics, the linear momentum conservation equation for a control volume can be written in the following form for a steady state flow with uniform properties across the inlets and outlets (Figure 6.2 ):

  FIGURE 6.2 Interaction of a fluid stream and a fixed blade.

  ∑ ​

  F →

  CV

  =

  ∑ ​

  V →

  out

  m ˙

  out

  −

  ∑ ​

  V →

  in

  m ˙

  in

  (6.1)

  where

  ∑ ​

  F →

  CV

  is the resultant force of the body forces and surface forces (forces that act on the volume such as weight and surface such as pressure force, respectively) exerted on the control volume (N),

  V →

  is the absolute velocity vector of the flows relative to an inertial reference frame (m/s), and

  m ˙

  is the mass flow rates of inlet and outlet flows (kg/s). Equation 6.1 indicates that the force exerted on the control volume is equal to the net rate of the linear momentum that accompanies the mass flows crossing the boundary of the control volume (the control surface). Note that in the blade analysis, we are interested in the force that is imposed by the flow on the blade, which is the reaction force of

  F →

  C V

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Incompressible Flow Turbomachines

  Design, Selection, Applications, and Theory

  • G.F. Round(Author)
  • 2004(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  The foregoing statement is not true of all turbines. Impulse Turbines, for example, are jet reaction turbines, and it is not possible to reverse the flow. 3.2 General Operating Conditions The best practical operating condition of a turbine is usually at constant speed, with a gate opening (controlling flow) that is dependent on the head across the machine. Variation of static head is 55 56 Incompressible Flow Turbomachines Pelton wheels Francis turbines Kaplan turbines 10,000 H,m 1000 100 10 N S 100 0 1 100 10 Figure 3-1 Broad classification of turbines. Head, H, across the turbine as a function of specific speed N S (Units: rpm, kW, m)—log-log plot. particularly important in low head plants where the tailwater level may rise in time of flood at a different rate to the headwater level, thus giving a significant decrease in power. Figure 3-2 shows typical efficiency curves at constant speed as a function of rated power for constant rotational speed and constant head. 3.3 Impulse Turbines-Pelton Wheels An Impulse Turbine is a turbomachine in which kinetic energy from one or more fast-moving jets is converted to rotational mechanical energy delivered to the shaft of the machine. Several types of Impulse Turbines have been invented, but only one has survived in appreciable numbers to the present day. This is the Pelton wheel. A typical Pelton wheel system is shown schematically in Figure 3-3. The high-speed jets of fluid impinge, in as shock-free a way as possible, on vanes or buckets located around the periphery of a wheel. Figure 3-4 shows a jet and the velocities associated with it. The energy delivered by the jet to the buckets is dissipated as head losses in several ways: 1. Nozzle head loss, given by: ( 1 / C 2 V − 1 )( V 2 1 / 2g ) (3.1) Turbines 57 d Overall efficiency, % % of rated power 100 90 80 70 60 50 40 100 90 80 70 60 50 40 30 20 c b a Figure 3-2 Efficiency as a function of rated power for different turbines.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Hydroelectric Energy

  Renewable Energy and the Environment

  • Bikash Pandey, Ajoy Karki(Authors)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  10 Impulse Turbines Impulse Turbines direct high-velocity jets at runner blades to convert kinetic energy to shaft power. Nozzles are used to transform the potential energy of the water to kinetic energy carried by the jets. Only a few of the blades of the runner interact with each jet at any time, and the discharge through an Impulse Turbine is largely independent of the speed of rotation of the runner. Other features that distinguish Impulse Turbines from reaction turbines are that (a) the change in water pressure occurs in the nozzles of the machine and not along the turbine rotor and (b) impingement of the jet on the runner and its rotation both take place at atmospheric pressure. Pelton turbines are the most widely used among Impulse Turbines covering a remarkable range from less than a kilowatt to single units producing hundreds of megawatts. In addition to Peltons, this chapter explores the Turgo and cross-flow Impulse Turbines, which cover the micro hydro to small hydro range from 1 kW typically up to 5 MW. The Pelton and Turgo are tangential flow turbines with jets striking the periphery of the runner and exiting from the sides whereas the cross-flow is a radial flow turbine with the water flowing along the radius toward the shaft of the runner after striking the first set of blades. 10.1  PELTON TURBINES Pelton turbines utilize high-velocity jets from one or more nozzles to strike buckets on a spinning runner. There are typically between 20 and 25 buckets mounted on the periphery of the runner shown in Figure 10.1. The buckets have the shape of two half bowls joined together with a sharp ridge between them. When the turbine is operating efficiently, upon hitting the bucket the jet loses most of its energy, and the exit velocity of the water is small

  Sign up to read

  Learn more about book
• 

  No longer available |Learn more

  Handbook of Gas and Pneumatics Technologies

  • (Author)
  • 2014(Publication Date)
  • Academic Studio

    (Publisher)

  Jet engines that produce thrust primarily from the direct impulse of exhaust gases are often called turbojets, whereas those that generate most of their thrust from the action of a ducted fan are often called turbofans or (rarely) fan-jets. Gas turbines are also used in many liquid propellant rockets, the gas turbines are used to power a turbopump to permit the use of lightweight, low pressure tanks, which saves considerable dry mass. ____________________ WORLD TECHNOLOGIES ____________________ Aeroderivative gas turbines Diagram of a high-pressure turbine blade Aeroderivatives are also used in electrical power generation due to their ability to startup, shut down, and handle load changes more quickly than industrial machines. They are also used in the marine industry to reduce weight. The General Electric LM2500, General Electric LM6000, Rolls-Royce RB211 and Rolls-Royce Avon are common models of this type of machine. Amateur gas turbines Increasing numbers of gas turbines are being used or even constructed by amateurs. In its most straightforward form, these are commercial turbines acquired through military surplus or scrapyard sales, then operated for display as part of the hobby of engine collecting. In its most extreme form, amateurs have even rebuilt engines beyond professional repair and then used them to compete for the Land Speed Record. The simplest form of self-constructed gas turbine employs an automotive turbocharger as the core component. A combustion chamber is fabricated and plumbed between the compressor and turbine sections. More sophisticated turbojets are also built, where their thrust and light weight are sufficient to power large model aircraft. The Schreckling design constructs the entire engine from raw materials, including the fabrication of a centrifugal compressor wheel from plywood, epoxy and wrapped carbon fibre strands. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Turbine Main Engines

  The Commonwealth and International Library: Marine Engineering Division

  • John B. Main, F. R. Harris, C. W. Herbert, A. J. S. Bennett(Authors)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  P A R T I MARINE STEAM TURBINES BY JOHN B. MAIN A . M . I . M e c h . E . , M . I . M a r . E . E X T R A FIRST-CLASS C E R T . This page intentionally left blank 1.1. Introduction P R I N C I P L E O F O P E R A T I O N T h e basic m o d e of operation of the steam turbine engine is extremely simple, being a direct derivation of torque, rotary motion, a n d consequently of power from the steam jet forces which are caused to act tangentially on the rotor blading. T h e steam jets are created in the conversion of the pressure energy of the ingoing steam into equivalent kinetic energy. This con-version is achieved in a series of steam passages or nozzles. S T E A M F L O W S t e a m flow t h r o u g h the nozzles occurs as the n a t u r a l conse-quence of a pressure difference existing between the nozzle inlet a n d outlet. For example, boiler pressure steam is applied at the inlet a n d condenser v a c u u m exists at the outlet. T h e geometry of the nozzle is m a d e such t h a t the cross-sectional area will contain, i.e. will properly a c c o m m o d a t e , the designed mass flow as the steam progressively drops in pressure, the flow accelerates, a n d the specific v o l u m e of the steam in-creases along the axis of the nozzle passage. T h e nozzle also guides the angle of the issuing steam jet. T H E E N E R G Y C O N V E R S I O N T h e torque developed on the turbine rotor derives from the tangential forces exerted u p o n the rotor periphery b y the rotor blading. 3 4 T U R B I N E M A I N E N G I N E S §1.1 Impulse Principle I n the impulse type of m a c h i n e the rotor blades form a com-plete ring or rings of U-shaped channels in which the steam jets from the nozzles are partially reversed in direction. T h e forces on the rotor blading are thus a function of the m a g n i t u d e of the change of velocity of the steam in the plane tangential to the blade ring a n d the steam mass rate of the flow.

  Sign up to read

  Learn more about book