1) Machine for increasing the pressure of a gas by mechanically decreasing its volume. Air is the most frequently compressed gas, but natural gas, oxygen, nitrogen, and other industrially important gases are also frequently compressed. There are three general types of compressors. Positive-displacement compressors are usually of the reciprocating piston type (see piston and cylinder), useful for supplying small amounts of a gas at relatively high pressures. Centrifugal compressors are particularly suited for compressing large volumes of gas to moderate pressures. Axial compressors are used for jet aircraft engines and gas turbines.
2). A machine that increases the pressure of a gas or vapor (typically air), or mixture of gases and vapors. The pressure of the fluid is increased by reducing the fluid specific volume during passage of the fluid through the compressor. When compared with centrifugal or axial-flow fans on the basis of discharge pressure, compressors are generally classed as high-pressure and fans as low-pressure machines.
Compressors are used to increase the pressure of a wide variety of gases and vapors for a multitude of purposes. A common application is the air compressor used to supply high-pressure air for conveying, paint spraying, tire inflating, cleaning, pneumatic tools, and rock drills. The refrigeration compressor is used to compress the gas formed in the evaporator. Other applications of compressors include chemical processing, gas transmission, gas turbines, and construction. See also Gas turbine; Refrigeration.
3). Compressor displacement is the volume displaced by the compressing element per unit of time and is usually expressed in cubic feet per minute (cfm). Where the fluid being compressed flows in series through more than one separate compressing element (as a cylinder), the displacement of the compressor equals that of the first element. Compressor capacity is the actual quantity of fluid compressed and delivered, expressed in cubic feet per minute at the conditions of total temperature, total pressure, and composition prevailing at the compressor inlet. The capacity is always expressed in terms of air or gas at intake (ambient) conditions rather than in terms of arbitrarily selected
4) Air compressors often have their displacement and capacity expressed in terms of free air. Free air is air at atmospheric conditions at any specific location. Since the altitude, barometer, and temperature may vary from one location to another, this term does not mean air under uniform or standard conditions. Standard air is at 68°F (20°C), 14.7 lb/in.2 (101.3 kilopascals absolute pressure), and a relative humidity of 36%. Gas industries usually consider 60°F (15.6°C) air as standard.
5) Compressors can be classified as reciprocating, rotary, jet, centrifugal, or axial-flow, depending on the mechanical means used to produce compression of the fluid, or as positive-displacement or dynamic-type, depending on how the mechanical elements act on the fluid to be compressed. Positive-displacement compressors confine successive volumes of fluid within a closed space in which the pressure of the fluid is increased as the volume of the closed space is decreased. Dynamic-type compressors use rotating vanes or impellers to impart velocity and pressure to the fluid.
6 )compressor, machine that decreases the volume of air or other gas by the application of pressure. Compressor types range from the simple hand pump and the piston-equipped compressor used to inflate tires to machines that use a rotating, bladed element to achieve compression. The four basic types of compressors are reciprocating, rotary screw, centrifugal, and axial-flow. These are further classified by the number of compression stages, the cooling method (air, water, or oil), the drive method (e.g., engine, motor, steam, gasoline, or diesel), and lubrication.
The most popular type is the reciprocating (or piston-and-cylinder) compressor, which is useful for supplying small amounts of a gas at relatively high pressures. In this type of compressor, a piston is driven within a cylinder; the gas is drawn in through an inlet valve on the suction stroke of the piston and is compressed and driven through another valve on the return stroke. Reciprocating compressors are either single- or double-acting. In single-acting machines the compression takes place on only one side of the piston; double-acting machines use both sides of the cylinder for compression. Multiple cylinder arrangements are common. The rotary-screw compressor uses two meshed rotating helical rotors within a casing to force the gas into a smaller space. Advantages of this type of compressor include smooth, pulse-free gas output with high output volume. The centrifugal compressor consists of a rotating impeller mounted in a casing and revolving at high speed. This causes a gas that is continuously admitted near the center of rotation to experience an outward flow and a pressure increase due to centrifugal action. Centrifugal compressors are particularly suited for compressing large volumes of gas to moderate pressures; they produce a smooth discharge of the compressed gas. In an axial-flow compressor, the gas flows over a set of airfoils spinning on a shaft in a tapered tube. These draw in gas at one end, compress it, and output it at the other end. Axial-flow compressors are used in jet aircraft engines and gas turbines.
Air is the most frequently compressed gas, although natural gas, oxygen, and nitrogen are also often compressed. Compressed air exerts an expansive force that can be used as a source of power to operate pneumatic tools or to control such devices as air brakes. Air under compression can be stored in closed cylinders to provide an continuous or as-needed supply of pressurized air.
DEFINETION:-
A rotor that draws air into the engine and is driven by a turbine. A compressor must provide the required pressure rise; the compression must be affected with the least possible loss; it must be aerodynamically stable over the operating range of RPM; and the tip speed must not approach too close to sonic speed. The two types of compressors are axial flow and centrifugal flow.
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