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Encyclopedia > Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. This article is about pressure in the physical sciences. ... For other uses, see Gas (disambiguation). ... For other uses, see Volume (disambiguation). ...

Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible, so the main action of a pump is to transport liquids. This article is about a mechanical device. ... A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... Pipe is a tube or hollow cylinder for the conveyance of fluid, gas and sometimes other materials. ...

The main types of gas compressors are illustrated and discussed below:

Image File history File links No higher resolution available. ...

### Centrifugal compressors

Figure 1: A single stage centrifugal compressor

Centrifugal compressors use a vaned rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants.[1][2][3] Their application can be from 100 hp (75 kW) to thousands of horsepower. With multiple staging, they can achieve extremely high output pressures greater than 10,000 psi (69 MPa). A centrifugal compressor, also called a radial blower, squirrel cage, or squirrel wheel compressor, consists of an axle to which is mounted a cylindrical assembly of compressor blades. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... An impeller is a rotor inside a tube or conduit to increase the pressure and flow of a fluid. ... Diffuser can refer to any device that diffuses in some manner such as: Diffuser (automotive), a shaped section of a cars underbody which improves the cars aerodynamic properties Diffuser (breathing set part), a device fitted over an underwater breathing sets blowoff hole to break up the resulting... View of Shell Oil Refinery in Martinez, California. ... A Chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. ... Petrochemicals are chemical products made from raw materials of petroleum (hydrocarbon) origin. ... A natural gas processing plant Natural gas processing plants are used to purify the raw natural gas extracted from underground gas fields and brought up to the surface by gas wells. ...

Many large snow-making operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium sized gas turbines. A ski area is a place where one goes to participate in the sports of skiing and snowboarding. ... Air foil bearing-supported turbocharger cutaway made by Mohawk Innovative Technology Inc. ... This machine has a single-stage centrifugal compressor and turbine, a recuperator, and foil bearings. ... For other uses, see Engine (disambiguation). ...

### Diagonal or mixed-flow compressors

Main article: Diagonal or mixed-flow compressor

Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to the axial direction. The diagonal compressor has a lower diameter diffuser than the equivalent centrifugal compressor. A diagonal or mixed-flow compressor is effectively a cross between a centrifugal and axial-flow compressor. ...

### Axial-flow compressors

Main article: Axial-flow compressor
An animation of an axial compressor.

Axial-flow compressors are dynamic rotating compressors that use arrays of fan-like aerofoils to progressively compress the working fluid. They are used where there is a requirement for a high flows or a compact design. The axial flow compressor is an improvement on the centrifugal compressor previously used in turbine engines,though small and micro turbines use centrifugal compressors with relative advantages (in terms of pressure ratios achieveable per stage of compression). ... Image File history File links Axial_compressor. ... Image File history File links Axial_compressor. ...

The arrays of aerofoils are set in rows, usually as pairs: one rotating and one stationary. The rotating aerofoils, also known as blades or rotors, decelerate and pressurise the fluid. The stationary aerofoils, also known as a stators or vanes, turn and decelerate the fluid; preparing and redirecting the flow for the rotor blades of the next stage.[1] Axial compressors are almost always multi-staged, with the cross-sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number. Beyond about 5 stages or a 4:1 design pressure ratio, variable geometry is normally used to improve operation. An F/A-18 Hornet breaking the sound barrier. ...

Axial compressors can have high efficiencies; around 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Axial-flow compressors can be found in medium to large gas turbine engines, in natural gas pumping stations, and within certain chemical plants. Polytropic fluids are idealized fluid models that are used often in astrophysics. ... This machine has a single-stage centrifugal compressor and turbine, a recuperator, and foil bearings. ...

### Reciprocating compressors

A motor-driven six-cylinder reciprocating compressor that can operate with two, four or six cylinders.

Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines.[1][4] [5] Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors up to 1000 hp are still commonly found in large industrial applications, but their numbers are declining as they are replaced by various other types of compressors. Discharge pressures can range from low pressure to very high pressure (>5000 psi or 35 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, noisier, and more costly than comparable rotary units.[6] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A motor-driven six-cylinder reciprocating compressor that can operate with two, four or six cylinders. ... For the American composer, see Walter Piston. ... This article is about a unit of measurement. ...

### Rotary screw compressors

Diagram of a rotary screw compressor

Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space.[1][7][8] These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 hp (2.24 kW) to over 500 hp (375 kW) and from low pressure to very high pressure (>1200 psi or 8.3 MPa). They are commonly seen with roadside repair crews powering air-tools. This type is also used for many automobile engine superchargers because it is easily matched to the induction capacity of a piston engine. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This article does not adequately cite its references or sources. ... A helix (pl: helices), from the Greek word Î­Î»Î¹ÎºÎ±Ï‚/Î­Î»Î¹Î¾, is a twisted shape like a spring, screw or a spiral (correctly termed helical) staircase. ... A supercharger (also known as a blower) is an air compressor used to force more air (and hence more oxygen) into the combustion chamber(s) of an internal combustion engine than can be achieved at ambient atmospheric pressure (natural aspiration). ... For the American composer, see Walter Piston. ...

### Rotary vane compressors

Rotary vane compressors consist of a rotor with a number of blades inserted in radial slots in the rotor. The rotor is mounted offset in a larger housing which can be circular or a more complex shape. As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing.[1] Thus, a series of decreasing volumes is created by the rotating blades. Rotary Vane compressors are, with piston compressors one of the oldest of compressor technologies. A rotary vane pump is a positive displacement pump that consists of variable-length, tensioned vanes mounted to a rotor that rotates inside of a cavity. ...

With suitable port connections, the devices may be either a compressor or a vacuum pump. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Dry vane machines are used at relatively low pressures (e.g., 2 bar) for bulk material movement whilst oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about 13 bar in a single stage. A rotary vane compressor is well suited to electric motor drive and is significantly quieter in operation than the equivalent piston compressor.

### Scroll compressors

Main article: Scroll compressor
Mechanism of a scroll pump

A scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases. The vane geometry may be involute, archimedean spiral, or hybrid curves.[9][10][11] They operate more smoothly, quietly, and reliably than other types of compressors in the lower volume range. A scroll compressor uses two interleaved spiral-shaped scrolls to compress a fluid. ... Image File history File links Two_moving_spirals_scroll_pump. ... Image File history File links Two_moving_spirals_scroll_pump. ... This article is about a mechanical device. ... A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... liquids are things you use when your constapated. ... For other uses, see Gas (disambiguation). ... In the differential geometry of curves, an involute of a smooth curve is another curve, obtained by attaching a string to the curve and tracing the end of the string as it is wound onto the curve. ... An Archimedean spiral is a curve which in polar coordinates (r, θ) can be described by the equation with real numbers a and b. ...

Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid or gas between the scrolls.

### Diaphragm compressors

Main article: Diaphragm compressor

A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in touch with the gas being compressed.[1] Membrane and piston rod A diaphragm compressor is a variant of the classic reciprocating compressor with backup and piston rings and rod seal. ...

Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications. Typical North America vehicles carry this diamond shape symbol, meaning it is running on compressed natural gas fuel. ...

A three-stage diaphragm compressor

The photograph included in this section depicts a three-stage diaphragm compressor used to compress hydrogen gas to 6,000 psi (41 MPa) for use in a prototype hydrogen and compressed natural gas (CNG) fueling station built in downtown Phoenix, Arizona by the Arizona Public Service company (an electric utilities company). Reciprocating compressors were used to compress the natural gas. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This article is about the chemistry of hydrogen. ... Typical North America vehicles carry this diamond shape symbol, meaning it is running on compressed natural gas fuel. ... Nickname: Location in Maricopa County and the state of Arizona Coordinates: , Country State County Maricopa Incorporated February 25, 1881 Government  - Type Council-Manager  - Mayor Phil Gordon (D) Area  - City  515. ... An electric utility subsidiary of the public company Pinnacle West. ... A motor-driven six-cylinder reciprocating compressor that can operate with two, four or six cylinders. ... For other uses, see Natural gas (disambiguation). ...

The prototype alternative fueling station was built in compliance with all of the prevailing safety, environmental and building codes in Phoenix to demonstrate that such fueling stations could be built in urban areas. The definition of alternative fuel varies according to the context of its usage. ...

## Temperature

Main article: Gas laws

Compression of a gas naturally increases its temperature. The gas laws are a set of laws that describe the relationship between thermodynamic temperature (T), pressure (P) and volume (V) of gases. ... For other uses, see Temperature (disambiguation). ...

In an attempt to model the compression of gas, there are two theoretical relationships between temperature and pressure in a volume of gas undergoing compression. Although neither of them model the real world exactly, each can be useful for analysis. A third method measures real-world results:

• Isothermal - This model assumes that the compressed gas remains at a constant temperature throughout the compression or expansion process. In this cycle, internal energy is removed from the system as heat at the same rate that it is added by the mechanical work of compression. Isothermal compression or expansion more closely models real life when the compressor has a large heat exchanging surface, a small gas volume, or a long time scale (i.e., a small power level). Compressors that utilize inter-stage cooling between compression stages come closest to achieving perfect isothermal compression. However, with practical devices perfect isothermal compression is not attainable. For example, unless you have an infinite number of compression stages with corresponding intercoolers, you will never achieve perfect isothermal compression.
• Adiabatic - This model assumes that no energy (heat) is transfered to or from the gas during the compression, and all supplied work is added to the internal energy of the gas, resulting in increases of temperature and pressure. Theoretical temperature rise is T2 = T1·Rc(k-1)/k, with T1 and T2 in degrees Rankine or kelvins, and k = ratio of specific heats (approximately 1.4 for air). R is the compression ratio; being the absolute outlet pressure divided by the absolute inlet pressure. The rise in air and temperature ratio means compression does not follow a simple pressure to volume ratio. This is less efficient, but quick. Adiabatic compression or expansion more closely model real life when a compressor has good insulation, a large gas volume, or a short time scale (i.e., a high power level). In practice there will always be a certain amount of heat flow out of the compressed gas. Thus, making a perfect adiabatic compressor would require perfect heat insulation of all parts of the machine. For example, even a bicycle tire pump's metal tube becomes hot as you compress the air to fill a tire.
• Polytropic - This model takes into account both a rise in temperature in the gas as well as some loss of energy (heat) to the compressor's components. This assumes that heat may enter or leave the system, and that input shaft work can appear as both increased pressure (usually useful work) and increased temperature above adiabatic (usually losses due to cycle efficiency). Compression efficiency is then the ratio of temperature rise at theoretical 100 percent (adiabatic) vs. actual (polytropic).

In the case of the fire piston and the heat pump, people desire temperature change, and compressing gas is only a means to that end. An isothermal process is a thermodynamic process in which the temperature of the system stays constant: Î”T = 0. ... In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid. ... For the idealized thermodynamic cycle for a steam engine, see Rankine cycle. ... For other uses, see Kelvin (disambiguation). ... The specific heat capacity (symbol c or s, also called specific heat) of a substance is defined as heat capacity per unit mass. ... A polytropic process is a thermodynamic process that a system undergoes that obeys the relation , where p is pressure, V is volume, n is any real number (polytropic exponent), and K is a constant. ... A fire piston is an ancient device which is used to start fires. ... A heat pump is a machine or device that moves heat from one location (the source) to another location (the sink), using work. ...

## Staged compression

Since compression generates heat, the compressed gas is to be cooled between stages making the compression less adiabatic and more isothermal. The inter-stage coolers cause condensation meaning water separators with drain valves are present. In the case of small reciprocating compressors, the compressor flywheel may drive a cooling fan that directs ambient air across the intercooler of a two or more stage compressor.

Because of mechanical limitations and to increase efficiency, most compressors utilize staged compression, usually with intercooling between stages. In the case of centrifugal compressors, commercial designs currently do not exceed more than a 3.5 to 1 ratio in any one stage. Because rotary screw compressors can make use of cooling lubricant to remove the heat of compression, they very often exceed a 9 to 1 ratio. For instance, in a typical diving compressor the air is compressed in three stages. If each stage has a compression ratio of 7 to 1, the compressor can output 343 times atmospheric pressure (7 x 7 x 7 = 343 Atmospheres).

## Prime movers

There are many options for the "prime mover" or motor which powers the compressor: For the philosophical/theological concept of a prime mover (that is, a self-existent being that is the ultimate cause or mover of all things), see cosmological argument. ...

A Siemens steam turbine with the case opened. ... A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ... A rotor of a modern steam turbine, used in a power plant A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into useful mechanical work. ... Kaplan turbine and electrical generator cut-away view. ... For other kinds of motors, see motor. ... The generation of AC electric power is commonly three phase, in which the waveforms of three supply conductors are offset from one another by 120°. These three conductors are commonly housed in a single conduit (e. ... City lights viewed in a motion blurred exposure. ... In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are 2Ï€/3 radians (120Â°,1/3 of a cycle) offset in time. ... Diesel engines in a museum Diesel generator on an oil tanker A diesel engine is an internal combustion engine which operates using the Diesel cycle. ... A Petrol engine or Gasoline engine is an internal combustion engine with spark-ignition designed to run on petrol (gasoline) and similar volatile fuels. ... A supercharger (also known as a blower) is an air compressor used to force more air (and hence more oxygen) into the combustion chamber(s) of an internal combustion engine than can be achieved at ambient atmospheric pressure (natural aspiration). ... Air foil bearing-supported turbocharger cutaway made by Mohawk Innovative Technology Inc. ...

## Applications

Gas compressors are used in various applications where either higher pressures or lower volumes of gas are needed:

Cabin pressurization is the active pumping of air into the cabin of an aircraft to increase the air pressure within the cabin. ... Figure 1: Components of a centrifugal fan A centrifugal fan is a mechanical device for moving air or other gases. ... Compressed air is used to refer to: Pneumatics, the use of pressurized gases to do work, as used in the Air car Breathing gas, often used in scuba diving, also to inflate buoyancy devices Compressed air can also be used for cooling using a vortex tube. ... Gas compression heat pumps using the Stirling cycle are commonly used to liquefy air in order to produce liquid nitrogen, oxygen, argon, etc. ... A fire piston is an ancient device which is used to start fires. ... A hydrogen compressor is a mechanical device that increases the pressure of hydrogen by reducing its volume. ... A liquid ring pump is a rotating positive displacement pump. ... A Roots Blower refers to a specific design of positive displacement vacuum pumpâ€. // General description The term derives from the Roots brothers who invented the rotary lobe pump more than a century ago. ... Air cylinder can also mean a gas cylinder used to store compressed air, often used for scuba diving. ... Pneumatic tubes, also known as capsule pipelines or Lamson tubes, are systems in which cylindrical containers are propelled through a network of tubes by compressed air or by vacuum. ... Wiktionary has a definition of: Pressurization Pressurization generally refers to the application of pressure in a given situation or environment; and more specifically refers to the process by which atmospheric pressure is maintained in an isolated or semi-isolated atmospheric environment (for instance, in an aircraft, or whilst Scuba diving). ... Vapor-compression refrigeration[1][2] is one of the many refrigeration methods available for use. ...

## References

1. ^ a b c d e f Perry, R.H. and Green, D.W. (Editors) (2007). Perry's Chemical Engineers' Handbook, 8th Edition, McGraw Hill. ISBN 0-07-142294-3.
2. ^ Dixon S.L. (1978). Fluid Mechanics, Thermodynamics of Turbomachinery, Third Edition, Pergamon Press. ISBN 0-08-022722-8.
3. ^ Aungier, Ronald H. (2000). Centrifugal Compressors A Strategy for Aerodynamic design and Analysis. ASME Press. ISBN 0-7918-0093-8.
4. ^ Bloch, H.P. and Hoefner, J.J. (1996). Reciprocating Compressors, Operation and Maintenance. Gulf Professional Publishing. ISBN 0-88415-525-0.
5. ^ Reciprocating Compressor Basics Adam Davis, Noria Corporation, Machinery Lubrication, July 2005
6. ^ Introduction to Industrial Compressed Air Systems
7. ^ Screw Compressor Describes how screw compressors work and include photographs.
8. ^ Technical Centre Discusses oil-flooded screw compressors including a complete system flow diagram
9. ^ Tischer, J., Utter, R: “Scroll Machine Using Discharge Pressure For Axial Sealing,” U.S. Patent 4522575, 1985.
10. ^ Caillat, J., Weatherston, R., Bush, J: “Scroll-Type Machine With Axially Compliant Mounting,” U.S. Patent 4767293, 1988.
11. ^ Richardson, Jr., Hubert: “Scroll Compressor With Orbiting Scroll Member Biased By Oil Pressure,” U.S. Patent 4875838, 1989.
Perrys Chemical Engineers Handbook was first published in 1934 and the seventh edition was published in 1997. ... The American Society of Mechanical Engineers (ASME) is a professional body, specifically an engineering society, focused on mechanical engineering. ...

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