Turbines And Compressors

Term Paper Title	Turbines And Compressors
# of Words	1391
# of Pages (250 words per page double spaced)	5.56

Turbines and Compressors

In engineering and more specifically thermodynamics there are a number of significant devices. This paper will discuss two of these devices: turbines and compressors.  These two devices are related in the fact that they have opposing functions.  A compressor uses energy to increase the pressure of a gas, whereas a turbine uses a fluid to produce energy.  Also, in this paper a particular type of turbine, the steam turbine, will be discussed in-depth.
Compressors
As mentioned before, the main function of a compressor is to intake a certain gas at one pressure and output the substance at a higher pressure. The way in which the compressor increases the pressure is by decreasing the specific volume of the inlet gas.  There are some characteristics that help to separate the different types of compressors.  The compressor�s displacement is the volume displaced by the compressing element per unit time and the measurement is usually expressed in cubic feet per minute.  Another characteristic is the compressor capacity, which is the actual quantity of fluid that is compressed and delivered in the process, also expressed in cubic feet per minute.
A calculated value for compressors is the compression efficiency.  The value is compared against two different theoretical values, the isothermal and the adiabatic.  If the compressor were theoretically isothermal, then it would maintain perfect cooling where the gas remains at the inlet temperature.  If the compressor is theoretically adiabatic, then no cooling occurs and the temperature of the gas rises steadily during the compression.  Also, in the adiabatic case, the desired higher pressure is attained sooner than in the isothermal case but more work is required in the adiabatic process.
     There are three main types of compressors: axial flow, reciprocating, and centrifugal.   In the axial flow model, the gas moves parallel to the rotor and uses moving blades to increase the pressure of the fluid.  In reciprocating, the gas is compressed by a reciprocating piston in a cylinder equipped with inlet and outlet valves.  Finally in the centrifugal model, a wheel an diffuser is used to speed up the gas in the wheel and slow it down in the diffuser while increasing the pressure. Figures 1-1 and 1-2 show examples of a centrifugal and reciprocating compressors.


Turbines
A turbine on the other hand is basically the opposite of a compressor.  Instead of requiring energy as in the compressor to work upon a gas, the turbine using a flowing fluid produces energy.  In a turbine, the energy of a moving fluid is converted by the machine into mechanical energy through the use of a rotary device.  The principle element of operation for all types of turbines is the impulse of the moving fluid. Turbines can be classified into two main types: impulse and reaction.  In the impulse turbine, the wheel of the machine is forced to rotate by the one or more high velocity jets of fluid striking the blades.  For reaction turbines, a pressure drop across a set of stationary vanes and a further pressure drop in the rotating wheel.  The majority of the energy in this type of turbine is produced in the reaction to the differences in pressure.  Only a small amount is attributed to the velocity of the fluid.   The figure 1-3 shows the differences between these two main types with examples of two types of hydraulic turbines.

The most common way in which to convert to mechanical energy from the rotating shaft of the turbine is a direct coupling to an electric generator.  Also in order to maintain a current with a given frequency to the generator, some type of control is needed to provide a constant speed of rotation on the wheel. One way to accomplish this is to control the quantity of fluid that is allowed to enter the turbine.  In order to control the quantity and speed of the fluid, a series of nozzles is one possible solution.
     The type of fluid that is used in the operation of a turbine determines the type.  The most common types are steam, gas, and hydraulic.  All us...

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