existing impulse turbine, a one-stage turbine set in an organic Rankine cycle portal7.info Turbine blades, and hence turbines having these types of blades, are classified as impulse or reaction. When moving blades are driven entirely by the impact of. “Turbine” is a general term for any device that extracts mechanical energy from a There are two main types of dynamic turbines: impulse turbines and reaction.
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PDF | Impulse turbine has been constructed to be used in the program of Hydraulic Machines, Faculty of Mechanical Engineering at the. The purpose of this experiment is to revise the concepts of turbine cycle, its practical is classified as a “simple, single stage, axial flow, impulse turbine”. The impulse shows the total result of applying force. Impulse turbine works on the same principle. It is mostly used at high heads. Today we will.
Hence, velocity is very less as compared to the previous case. Velocity Diagram[ edit ] FigVelocity Diagram of Pressure compounded Impulse Turbine The velocity diagram shown in figure 4 gives a detail about the various components of steam velocity and Blade velocity. This indicates that the whirl velocity of fluid at exit of all stages is zero, which is in compliance with the optimum velocity concept as discussed earlier. The ratio of work produced in different stages is similar to as discussed for the above type. Disadvantages of Pressure Compounding[ edit ] The disadvantage is that since there is pressure drop in the nozzles, it has to be made air-tight.
Nozzles move due to both the impact of steam on them and the reaction due to the high-velocity steam at the exit. A turbine composed of moving nozzles alternating with fixed nozzles is called a reaction turbine or Parsons turbine.
Except for low-power applications, turbine blades are arranged in multiple stages in series, called compounding , which greatly improves efficiency at low speeds.
Multiple reaction stages divide the pressure drop between the steam inlet and exhaust into numerous small drops, resulting in a pressure-compounded turbine. Impulse stages may be either pressure-compounded, velocity-compounded, or pressure-velocity compounded. A pressure-compounded impulse stage is a row of fixed nozzles followed by a row of moving blades, with multiple stages for compounding. This is also known as a Rateau turbine, after its inventor.
A velocity-compounded impulse stage invented by Curtis and also called a "Curtis wheel" is a row of fixed nozzles followed by two or more rows of moving blades alternating with rows of fixed blades. This divides the velocity drop across the stage into several smaller drops. This was more efficient with high-pressure steam due to reduced leakage between the turbine rotor and the casing. The steam from the boilers enters from the right at high pressure through a throttle , controlled manually by an operator in this case a sailor known as the throttleman.
It passes through five Curtis wheels and numerous reaction stages the small blades at the edges of the two large rotors in the middle before exiting at low pressure, almost certainly to a condenser. The condenser provides a vacuum that maximizes the energy extracted from the steam, and condenses the steam into feedwater to be returned to the boilers.
On the left are several additional reaction stages on two large rotors that rotate the turbine in reverse for astern operation, with steam admitted by a separate throttle. Since ships are rarely operated in reverse, efficiency is not a priority in astern turbines, so only a few stages are used to save cost. Blade design challenges[ edit ] A major challenge facing turbine design was reducing the creep experienced by the blades. Because of the high temperatures and high stresses of operation, steam turbine materials become damaged through these mechanisms.
As temperatures are increased in an effort to improve turbine efficiency, creep becomes significant.
To limit creep, thermal coatings and superalloys with solid-solution strengthening and grain boundary strengthening are used in blade designs. Protective coatings are used to reduce the thermal damage and to limit oxidation.
These coatings are often stabilized zirconium dioxide -based ceramics. Using a thermal protective coating limits the temperature exposure of the nickel superalloy.
This reduces the creep mechanisms experienced in the blade. Oxidation coatings limit efficiency losses caused by a buildup on the outside of the blades, which is especially important in the high-temperature environment. The microstructure of these alloys is composed of different regions of composition.
A uniform dispersion of the gamma-prime phase — a combination of nickel, aluminum, and titanium — promotes the strength and creep resistance of the blade due to the microstructure.
The addition of these elements reduces the diffusion of the gamma prime phase, thus preserving the fatigue resistance, strength, and creep resistance.
These turbines exhaust steam at a pressure below atmospheric. These types include condensing, non-condensing, reheat, extraction and induction. Condensing turbines are most commonly found in electrical power plants. These turbines receive steam from a boiler and exhaust it to a condenser.
Non-condensing or back pressure turbines are most widely used for process steam applications, in which the steam will be used for additional purposes after being exhausted from the turbine.
The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are needed. Reheat turbines are also used almost exclusively in electrical power plants.
In a reheat turbine, steam flow exits from a high-pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.
Using reheat in a cycle increases the work output from the turbine and also the expansion reaches conclusion before the steam condenses, thereby minimizing the erosion of the blades in last rows. In most of the cases, maximum number of reheats employed in a cycle is 2 as the cost of super-heating the steam negates the increase in the work output from turbine.
Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feedwater heaters to improve overall cycle efficiency.
Extraction flows may be controlled with a valve, or left uncontrolled. Extracted steam results in a loss of power in the downstream stages of the turbine.
Induction turbines introduce low pressure steam at an intermediate stage to produce additional power. Casing or shaft arrangements[ edit ] These arrangements include single casing, tandem compound and cross compound turbines.
Single casing units are the most basic style where a single casing and shaft are coupled to a generator.
Tandem compound are used where two or more casings are directly coupled together to drive a single generator. A cross compound turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. There may be one or more jets striking equal number of buckets simultaneously. Water is admitted over the entire circumference of the runner.
Water completely fills at the passages between the blades and while flowing between inlet and outlet sections does work on the blades. Reaction turbine are generally connected to the tail race through a draft tube which is a gradually expanding passage.
It may be installed below or above the tail race. The flow regulation in reaction turbine is carried out by means of a guide-vane assembly. Other component parts are scroll casing, stay ring runner and the draft tub. Reaction turbine have relatively less efficiency. Reaction turbine operate at low and medium heads. Water flows in radial and axial direction to turbine wheel.