Turbomachinery

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Information about Turbomachinery

Published on April 27, 2014

Author: bmerchant96

Source: slideshare.net

Turbomachinery Merchant Bilal A 1 Kalsekar Polytechnic Address Mechanical Department, 2nd year (inst.code-1608) 1bmerchant96@yahoo.in Abstract— A turbopump in a rocket engine consists of a pump that delivers fuel or oxidizer to the thrust chamber where the propellants are brought to react and increase in temperature. Since the combustion process takes place under constant pressure, the chamber pressure is the net result of the turbopump system. Turbomachinery for liquid rocket propulsion shares many of the design features and challenges found in gas turbines. To an even greater extent than in jet-engines used for aircraft the emphasis is on delivering very high power in a small machine. Pumps and turbines are classical subjects of engineering and are in wide spread use in many areas. Keywords—Turbomacine, stator, rotor, dynamic, impeller, etc. I. INTRODUCTION The turbomachine has been defined differently by different authors, though these definitions are similar and nearly equivalent. According to Daily [1], the turbomachine is a device in which energy exchange is accomplished by hydrodynamic forces arising between a moving fluid and the rotating and stationary elements of the machine. According to Wislicenus [2], a turbomachine is characterized by dynamic energy exchange between one or several rotating elements and a rapidly moving fluid. Binder [3] states that a turbomachine is characterized by dynamic action between a fluid and one or more rotating elements. A definition to include the spirit of all the preceding definitions would be: A turbomachine is a device in which energy transfer occurs between a flowing fluid and a rotating element due to dynamic action resulting in a change in pressure and momentum of the fluid. Mechanical energy transfer occurs into or out of the turbomachine, usually in steady flow. Turbomachines include all those types that produce large-scale power and those that produce a head or pressure, such as centrifugal pumps and compressors. Fig. 1 II. USES OF TURBOMACHINES The turbomachine is used in several applications, the primary ones being electrical power generation, aircraft propulsion and vehicular propulsion for civilian and military use. The units used in power generation are steam, gas and hydraulic turbines, ranging in capacity from a few kilowatts to several hundred and even thousands of megawatts, depending on the application. Here, the turbomachine drives the alternator at the appropriate speed to produce power of the right frequency. In aircraft and heavy vehicular propulsion for military use, the primary driving element has been the gas turbine. III. CLASSIFICATION OF TUBOMACHINES Turbomachines are classified into five basic types on the basis of the following, a. Energy transfer i. Power generating turbo machines-Turbines ii. Power absorbing turbo machines-Pumps b. Direction of flow i. Axial Flow ii. Radial Flow iii. Mixed Flow iv. Tangential Flow c. Condition of fluid i. Impulse type (constant pressure)-Pelton wheel turbine ii. Reaction type (variable pressure)- Francis turbine d. Position of rotating shaft i. Horizontal shaft – Steam turbines ii. Vertical shaft – Kaplan water turbines iii. Inclined shaft – Modern bulb micro- hydel turbines IV. COMPONENTS OF TURBOMACHINES The principal components of a turbomachine are: (i) A rotating element carrying vanes operating in a stream of fluid, (ii) A stationary element or elements which generally act as guide vanes or passages for the proper control of flow direction and the energy conversion process, (iii) an input and/or an output shaft, and (iv) a housing (Fig. 2). The rotating element carrying the vanes is also known by the names rotor, runner, impeller, etc., depending upon the particular application. Energy transfer occurs only due to the exchange of momentum between the flowing fluid and the rotating

elements; there may not be even a specific boundary that the fluid is not permitted to cross. Fig. 2 V. MECHANICAL DRAWBACK The mechanical design is highly complex both in static and rotating parts. The main difficulty in the static parts is the severe thermal transients encountered on start and stop transients. Parts designed for burst become thick walled due to high pressures suffer from the thermal gradients encountered during transients. This causes a conflict in the designs that are hard to solve and demands a lot of work and design experience. In order to be efficient and have high power output the blades must move at high speed. VI. BLADE VIBRATION Blade vibration is most definitely one of the major design concerns for the turbine. Blade vibration problems in general constitute the probably largest source of difficult problems late in the design project. Fig. 3 VII. RECENT DEVELOPMENT AND TRENDS By 1940, single turbine units with a power capacity of 100,000 kilowatts were common. Ever-larger turbines (with higher efficiencies) have been constructed during the last half of the century, largely because of the steadily rising cost of fossil fuels. This required a substantial increase in steam generator pressures and temperatures. Some units operating with supercritical steam at pressures as high as 34,500 kilopascals gauge and at temperatures of up to 650 °C were built before 1970. Reheat turbines that operate at lower pressures (between 17,100 to 24,100 kilopascals gauge) and temperatures (540–565 °C) are now commonly installed to assure high reliability. Steam turbines in nuclear power plants, which are still being constructed in a number of countries outside of the United States, typically operate at about 7,580 kilopascals gauge and at temperatures of up to 295 °C to accommodate the limitations of reactors. Turbines that exceed one-million-kilowatt output require exceptionally large, highly alloyed steel blades at the low pressure end. Fig. 4 VIII. CONCLUSION Turbomachinery has its application more in conventional machine having adequate efficiency and performance. Thus they have their various applications in displacement of fluid, electricity generation, etc. REFERENCES [1] Daily, J.W., Hydraulic Machinery, Part 13, Engineering Hydraulics, Ed. H. Rouse, Wiley, 1950. [2] Wislicenus, G.F., Fluid Mechanics of Turbomachinery, McGraw- Hill, 1947. [3] Binder, R.C., Advanced Fluid Mechanics, Vol. I, Prentice-Hall, 1958.

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