Technology & Engineering
Reaction Turbine
A reaction turbine is a type of turbine that converts the energy from a fluid into mechanical energy. It operates on the principle of reacting to the fluid's pressure or flow. The fluid enters the turbine and is directed through fixed and moving blades, causing the rotor to spin and generate power.
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eBook - PDFRadial Flow Turbocompressors
Design, Analysis, and Applications
- Michael Casey, Chris Robinson(Authors)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
The turbine rotor turns the absolute flow velocities from the circumferential direction against the direction of rotation back towards the meridional direction. 1.3.5 Degree of Reaction The degree of reaction for a turbomachinery stage describes the relative pressure rise (or fall) in the rotor compared to that of the stage. This is often discussed in the context of steam turbines where Reaction Turbines and impulse designs with no reaction can be found. In the history of steam turbines, both types were invented independently, the Reaction Turbine by Sir Charles Parsons (1854–1931) and the impulse turbine by Gustaf de Laval (1845–1913). The Reaction Turbine, as the name implies, is turned by reactive force rather than by a direct push or impulse. An impulse turbine has fixed nozzles (stator blades) that orient the fluid flow into high- speed jets. These jets contain significant kinetic energy, and the rotor blades, shaped symmetrically like buckets, convert this into shaft rotation as the jet changes direction. A pressure drop occurs in the nozzle, but the pressure is the same when the flow enters and leaves the rotor blade, and this gives rise to an impulse machine with zero degree of reaction. In a Reaction Turbine, the rotor makes use of the reaction force produced as the fluid accelerates through the rotor blades. The fluid is directed on to the rotor by the fixed vanes of the stator. It leaves the stator as a stream that fills the entire circumference of the rotor. In a reaction machine, the pressure change occurs across both the stator and the rotor. Centrifugal compressors with no inlet swirl are reaction machines and generally have a degree of reaction close to 0.6 indicating that about 60% of the overall static pressure rise of the stage takes place in the rotor, Figure 1.3. 1.3.6 Boundary of the Flow Field Turbomachines can also be classified with respect to configurations with and without a casing.
eBook - ePub- D. Yogi Goswami, Frank Kreith, D. Yogi Goswami, Frank Kreith(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
12Hydraulic 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 InformationA 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.
No longer available |Learn moreAdvanced Thermodynamics
Fundamentals, Mathematics, Applications
- Mehrzad Tabatabaian, R. K. Rajput(Authors)
- 2017(Publication Date)
- Mercury Learning and Information(Publisher)
In this type of turbine kinetic energy of the steam changes but the enthalpy remains constant. 2. Reaction: when steam flows through airfoil-shaped blades and moves the rotor due to the pressure difference created. Steam flows through the turbine similar to a meandering jet stream, and hence moves the rotors at several stages. 3. Combination of impulse and reaction: as the name indicates, this is a combination of types (1) and (2). Further, turbines are also classified as follows: 1. According to the number of pressure stages: • Single-stage turbines with one or more velocity stages are usually of small power capacities; these turbines are mostly used for driving centrifugal compressors, blowers, and other similar machinery. • Multistage impulse and Reaction Turbines; they are made in a wide range of power capacities varying from small to large. 2. According to the direction of steam flow: • Axial turbines in which steam flows in a direction parallel to the axis of the turbine. • Radial turbines in which steam flows in a direction perpendicular to the axis of the turbine; one or more low-pressure stages in such turbines are made axial. STEAM TURBINES • 383 3. According to the number of cylinders: • Single cylinder turbines. • Double cylinder turbines. • Three cylinder turbines. • Four cylinder turbines. Multi-cylinder turbines which have their rotors mounted on one and the same shaft and are coupled to a single generator are known as single shaft turbines; turbines with separate rotor shafts for each cylinder placed parallel to each other are known as multiaxial turbines. 4. According to the method of governing: • Turbines with throttle governing in which fresh steam enters through one or more (depending on the power developed) simultaneously operated throttle valves. • Turbines with nozzle governing in which fresh steam enters through two or more consecutively opening regulators.
eBook - ePub- Don M. Pirro, Martin Webster, Ekkehard Daschner(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
(As a result of this expansion to provide steam velocity, this arrangement may be referred to as a 50% Reaction Turbine.) The moving blades form the walls of moving nozzles that are designed to permit further expansion of the steam and to partially reverse the direction of steam flow, which produces the reaction on the blades. The distinguishing characteristic of the Reaction Turbine is that a pressure drop occurs across both the moving and stationary nozzles, or blades (Figure 14.2). Normally, Reaction Turbines use a considerable number of rows of moving and stationary nozzles through which steam flows as its initial pressure is reduced to exhaust pressure. The pressure drop across each row of nozzles is, therefore, relatively small, and steam velocities are correspondingly moderate, permitting medium rotating speeds. Reaction stages are usually preceded by an initial velocity compounded impulse stage, as in Figure 14.2, in which a relatively large pressure drop takes place. This results in a shorter, less costly turbine. In the radial flow reaction, or Ljungstrom, turbine, instead of the steam flowing axially through alternating rows of fixed and moving blades, it flows radially through several rows of reaction blades. Alternate rows of blades move in opposite directions. They are fastened to two independent shafts that operate in opposite directions, each shaft driving a load. FIGURE 14.1 Turbine with impulse blading. Velocity compounding is accomplished in the first two stages by two rows of moving blades between which is placed a row of stationary blades that reverses the direction of steam flow as it passes from the first to the second row of moving blades
eBook - PDFTurbomachinery
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.
eBook - ePubHydroelectric Energy
Renewable Energy and the Environment
- Bikash Pandey, Ajoy Karki(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
11 Reaction TurbinesRotation of the runner in a Reaction Turbine results from the reaction to its blades changing the direction and momentum of the water flow. The flow in Reaction Turbines is continuous over the length of the water passage with the runner rotating immersed in water flowing continuously over all its blades. Figure 11.1 shows an example of how all the blades of a Reaction Turbine, in this case a Kaplan, are in the water and simultaneously interacting with the flow. This is markedly different from impulse turbines with which the runner rotates in the air with a few of the buckets interacting with a high-velocity jet of water at any one time. The simultaneous application of torque on all the blades of a Reaction Turbine results in significantly more power produced per unit head compared to an impulse turbine using the same sized runner.Reaction Turbine runners are designed to make use of both the pressure energy and kinetic energy of the water flow. The inlet structure, consisting of a spiral casing and a wicket gate with guide vanes designed to introduce swirl or circulation as the water enters the runner, typically transforms only a part of the hydraulic pressure into kinetic energy as the water passes through it. As a result, the flow velocity at the runner inlet is relatively low for Reaction Turbines compared to impulse turbines. The runner converts the remaining pressure head to kinetic energy and ultimately transforms both the pressure and velocity of the water into mechanical power. To extract the maximum power from the available head, hydraulic pressure is often below atmospheric when the water exits the runner. This is accomplished through the use of a draft tube, described in Section 11.2 .Reaction Turbines have higher specific speeds than impulse turbines—that is, for similar head and power output conditions, Reaction Turbines run at significantly higher speeds. The most widely used Reaction Turbine designs are the Francis, Kaplan, and propeller. In recent years, compact tubular bulb turbines have become popular for low and very low head applications. Francis turbines, which utilize radial–axial flow, are used across a large range of medium heads (40–700 m) whereas Kaplan and propeller turbines utilize axial flow and are suitable for low head sites (10–80 m).
eBook - PDF- John Ward-Smith(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
The converse action results from an increase of speed. The runner of a Reaction Turbine is always full of the working fluid, whereas in an impulse machine only a few of the runner blades are in use at any one moment. The Reaction Turbine is therefore able to deal with a larger quantity of fluid for a given size of runner. For a runner of given diameter the greatest Turbines 607 Fig. 13.14 Axial-flow (propeller) turbine. rate of flow possible is achieved when the flow is parallel to the axis. Such a machine is known as an axial-flow Reaction Turbine or propeller turbine. From Fig. 13.14 it will be seen that the arrangement of guide vanes for a propeller turbine is (usually) similar to that for a Francis machine. The function of the vanes is also similar: to give the fluid an initial motion in the direction of whirl. Between the guide vanes and the runner, the fluid in a propeller turbine turns through a right-angle into the axial direction and then passes through the runner. The latter usually has four or six blades and closely resembles a ship’s propeller. Apart from frictional effects, the flow approaching the runner blades is that of a free vortex (whirl velocity inversely proportional to radius) whereas the velocity of the blades them-selves is directly proportional to radius. To cater for the varying relation between the fluid velocity and the blade velocity as the radius increases, the blades are twisted, the angle with the axis being greater at the tip than at the hub. The blade angles may be fixed if the available head and the load are both fairly constant, but where these quantities may vary a runner is used on which the blades may be turned about their own axes while the machine is running. When both guide-vane angle and runner-blade angle may thus be varied, a high efficiency can be maintained over a wide range of operating conditions. Such a turbine is known as a Kaplan turbine after its inventor, the Austrian engineer Viktor Kaplan (1876–1934).
eBook - PDF- G R Jones(Author)
- 2013(Publication Date)
- Newnes(Publisher)
The shape of runners corresponding to progressively higher heads are shown from left to right. With the advent of physically large units operating at very low and varying heads, as encountered on some run of river schemes and on tidal applications, yet another variation on the design of an axial flow turbine has been introduced. This type of turbine, known as a 'Kapeller', has fixed guide vanes but the runner is equipped with movable runner blades. Such a combination produces a plateau of relatively high turbine efficiencies, along the line of maximum output for a substan-tial range of heads. In an impulse turbine all the available energy is converted into velocity, before the water enters the runner, while in a Reaction Turbine the process of conversion takes place partly before and partly after the water has entered the runner. The division of water turbines into these two groups is based on general usage and does not imply any difference in the method of energy transfer between the water and the runner. At its simplest the principle of a water turbine is that of a rotating duct, through which flows a stream of water. The stream and the duct interact; the stream is deflected and, as a result, a force is exerted on the duct. The moment of this force, about the axis of rotation of the duct is equal and opposite to the change in the moment of momentum of the stream. If the mass of water, flowing in a unit of time is £ß, the driving torque M is given by M = tQ{r x C Ux -r 2 C U2 ) (17.4) where C Ul and C U2 are the whirl velocities at the inlet and exit, and r x and r 2 are the corresponding radii. Note that only the whirl components of the absolute velocities of flow contribute to the driving torque.
eBook - PDF- S. C. McBirnie(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
S T E A M T U R B I N E T H E O R Y 5 2 7 This steam flow is then used in the stage calculations as previously illustrated, the calculated expansion line built up stage by stage on the Mollier Diagram, and the turbine internal efficiency ratio ultimately found. If this differs significantly from that originally assumed, the steam flow and the condition curve are modified and the calculations repeated until agreement is reached. If steam for feed heating is to be extracted from some of the turbine stages, then the steam flows through the various sections of the turbines must be modified accordingly (see Chapters 11 and 12). These processes can be quite complex, involving as they do, many interdependent factors and much repetitive work, and nowadays are tending more to be carried out by computer methods. A computer, however, can do the repetitive work and satisfy all the interdependent factors, only if it is pro-grammed to do so by someone who has done the fundamental work outlined, albeit comparatively briefly, in this and other chapters. Modern steam turbine development is such that it is no longer strictly correct to classify turbines as impulse or re-action, implying that either all or half respectively of the stage adiabatic enthalpy drop takes place in the nozzles. So-called Reaction Turbines have always had approximately 50 per cent reaction, and nowadays most so-called impulse stages have some reaction. To be correct a stage is defined by its u/C 0 and its degree of reaction. Even so, the terms impulse and reaction tend to remain, but where used, they should be understood to mean the class of blade used; i.e. whether an impulse type such as that shown in Figure 10.42 or a reaction type such as shown in Figure 10.49. Reference to Figure 10.64 will show that for the given conditions, the change-over point is U/CQ = 0.55 and 21 per cent reaction i.e. below these values we should use impulse-type blades, and above we should use reaction-type blades.
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