Turbine Vst

[Thomasina Norse]

Theword "turbine" was coined in 1822 by the French mining engineer Claude Burdin from the Greek τύρβη, tyrbē, meaning "vortex" or "whirling", in a memo, "Des turbines hydrauliques ou machines rotatoires grande vitesse", which he submitted to the Acadmie royale des sciences in Paris.[4] Benoit Fourneyron, a former student of Claude Burdin, built the first practical water turbine.

A working fluid contains potential energy (pressure head) and kinetic energy (velocity head). The fluid may be compressible or incompressible. Several physical principles are employed by turbines to collect this energy:

Impulse turbines change the direction of flow of a high velocity fluid or gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is no pressure change of the fluid or gas in the turbine blades (the moving blades), as in the case of a steam or gas turbine, all the pressure drop takes place in the stationary blades (the nozzles). Before reaching the turbine, the fluid's pressure head is changed to velocity head by accelerating the fluid with a nozzle. Pelton wheels and de Laval turbines use this process exclusively. Impulse turbines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blades on the rotor. Newton's second law describes the transfer of energy for impulse turbines. Impulse turbines are most efficient for use in cases where the flow is low and the inlet pressure is high. [3]

Reaction turbines develop torque by reacting to the gas or fluid's pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades.[3] A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (such as with wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages are usually used to harness the expanding gas efficiently. Newton's third law describes the transfer of energy for reaction turbines. Reaction turbines are better suited to higher flow velocities or applications where the fluid head (upstream pressure) is low. [3]

In the case of steam turbines, such as would be used for marine applications or for land-based electricity generation, a Parsons-type reaction turbine would require approximately double the number of blade rows as a de Laval-type impulse turbine, for the same degree of thermal energy conversion. Whilst this makes the Parsons turbine much longer and heavier, the overall efficiency of a reaction turbine is slightly higher than the equivalent impulse turbine for the same thermal energy conversion.

In practice, modern turbine designs use both reaction and impulse concepts to varying degrees whenever possible. Wind turbines use an airfoil to generate a reaction lift from the moving fluid and impart it to the rotor. Wind turbines also gain some energy from the impulse of the wind, by deflecting it at an angle. Turbines with multiple stages may use either reaction or impulse blading at high pressure. Steam turbines were traditionally more impulse but continue to move towards reaction designs similar to those used in gas turbines. At low pressure the operating fluid medium expands in volume for small reductions in pressure. Under these conditions, blading becomes strictly a reaction type design with the base of the blade solely impulse. The reason is due to the effect of the rotation speed for each blade. As the volume increases, the blade height increases, and the base of the blade spins at a slower speed relative to the tip. This change in speed forces a designer to change from impulse at the base, to a high reaction-style tip.

Classical turbine design methods were developed in the mid 19th century. Vector analysis related the fluid flow with turbine shape and rotation. Graphical calculation methods were used at first. Formulae for the basic dimensions of turbine parts are well documented and a highly efficient machine can be reliably designed for any fluid flow condition. Some of the calculations are empirical or 'rule of thumb' formulae, and others are based on classical mechanics. As with most engineering calculations, simplifying assumptions were made.

Velocity triangles can be used to calculate the basic performance of a turbine stage. Gas exits the stationary turbine nozzle guide vanes at absolute velocity Va1. The rotor rotates at velocity U. Relative to the rotor, the velocity of the gas as it impinges on the rotor entrance is Vr1. The gas is turned by the rotor and exits, relative to the rotor, at velocity Vr2. However, in absolute terms the rotor exit velocity is Va2. The velocity triangles are constructed using these various velocity vectors. Velocity triangles can be constructed at any section through the blading (for example: hub, tip, midsection and so on) but are usually shown at the mean stage radius. Mean performance for the stage can be calculated from the velocity triangles, at this radius, using the Euler equation:

Modern turbine design carries the calculations further. Computational fluid dynamics dispenses with many of the simplifying assumptions used to derive classical formulas and computer software facilitates optimization. These tools have led to steady improvements in turbine design over the last forty years.

The primary numerical classification of a turbine is its specific speed. This number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate. The specific speed is derived to be independent of turbine size. Given the fluid flow conditions and the desired shaft output speed, the specific speed can be calculated and an appropriate turbine design selected.

Gas turbines have very high power densities (i.e. the ratio of power to mass, or power to volume) because they run at very high speeds. The Space Shuttle main engines used turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The liquid hydrogen turbopump is slightly larger than an automobile engine (weighing approximately 700 lb) with the turbine producing nearly 70,000 hp (52.2 MW).

A turbine is a device that harnesses the kinetic energy of some fluid - such as water, steam, air, or combustion gases - and turns this into the rotational motion of the device itself.[2] Turbines are generally used in electrical generation, engines, and propulsion systems. Turbines are machines (specifically turbomachines) because turbines transmit and modify energy. A simple turbine is composed of a series of blades - currently steel is one of the most common materials used - and allows the fluid to enter the turbine, pushing the blades. These blades spin while the fluid flows through, capturing some of the energy as rotational motion. Fluid flowing through a turbine loses kinetic energy and exits the turbine with less energy than it started with.[2]

Turbines are used in many different areas, and each type of turbine has a slightly different construction to perform its job properly. Turbines are used in wind power, hydropower, in heat engines, and for propulsion. Turbines are extremely important because of the fact that nearly all electricity is produced by turning mechanical energy from a turbine into electrical energy via a generator.[2]

Gas turbines are used frequently in heat engines as they are one of the most flexible types of turbines. One specific application of these gas turbines is in jet engines.[2] In these gas turbines, compressed air is heated and mixed with some fuel. When this mixture ignites it undergoes rapid expansion. The expanding air is pushed into the turbine, causing it to spin. Since they use compressed air, high altitudes do not affect the efficiency of the turbines, making them ideal for use in airplanes.[3]. A diagram of a gas turbine is shown in Figure 2 below.

In a hydroelectric facility, water is held behind a dam and is released through a penstock. The water, which has kinetic and potential energy, is allowed to fall on a turbine which spins a shaft connected to a generator, thus generating electricity. These turbines are essential in the area of hydropower - the process of obtaining power from water.

The construction of hydroelectric turbines is similar for different types of hydroelectric plants (see run-of-the-river hydroelectricity and impoundment for more information). A row of blades is fitted to some rotating shaft or plate. Water is then passed through the turbine over the blades, causing the inner shaft to rotate. This rotational motion is then transferred to a generator where electricity is generated. There are a variety of different types of turbines that are best used in different situations. Each type of turbine is created to provide maximum output for the situation it is used in (examples of different types of hydropower turbines include francis turbines, kaplan turbines and pelton turbines). There are many factors that must be investigated to determine which turbine should be used. These factors include hydraulic head, hydroelectric discharge, and the cost.[6]

Two types of turbines are generally found in these facilities, and the choice of which to use depends on the characteristics of the hydroelectric facility. These types are reaction turbines and impulse turbines. For more information on how these turbines work and more detailed information on other turbines, click here.

Wind turbines operate by transforming the kinetic energy in wind into mechanical power which is used to generate electricity by spinning a generator. These turbines can be on land, or can be offshore wind turbines. These turbines have three main components. The first of these are the rotor blades which are shaped like aircraft wings to catch the air, causing the blades to turn. The second component is the nacelle, a set of gears and a generator that transforms the blade rotation into electrical energy. Finally, the tower is the large stand that the blades and nacelle are mounted on.[8]

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