(C)ompressor
COMPRESSOR :
Compressor, device 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 compressed. Compressors supply the air
flow for all equipment in a system. Air compressors work in two phases: the
compression operation and the release operation.
The purpose of an air compressor is to convert power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure.
Working of a compressor :
 |
Heart
of the air conditioning system
The Air Conditioning Process
Your air conditioner pulls warm air through return air vents in rooms throughout your house. Coils in the evaporator unit, which are filled with a gaseous refrigerant, absorb heat. The heat-filled refrigerant is pumped outdoors to the condenser unit so that the heat can be released. The refrigerant travels back to the evaporator where the process begins again.
The Role of the Compressor
When refrigerant leaves an air conditioner’s evaporator, it takes the form of low-pressure gas. To release the heat the refrigerant has absorbed, the refrigerant needs to be in a higher temperature, higher pressure form. The compressor packs molecules in the gas-based refrigerant tightly together, a process which raises both the temperature and pressure of the refrigerant. Since heat moves from warm to cool surfaces, the heat that’s now in the high-temperature refrigerant moves to the cooler air outdoors where it can be released through the condenser
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; while some can be compressed, the
main action of a pump is to pressurize and transport liquids.
Many compressors can be staged, that
is, the fluid is compressed several times in steps or stages, to increase
discharge pressure. Often, the second stage is physically smaller than the primary
stage, to accommodate the already compressed gas. Each stage further
compresses the gas and increases pressure. Those that are powered
by an electric motor can also
be controlled using a VFD or power inverter, however many (hermetic and
semi-hermetic) compressors can only work at certain speeds, since they may
include built-in oil pumps. The oil pumps are connected to the same shaft that
drives the compressor and forces oil into the compressor and motor bearings.
At low speeds, insufficient quantities or no oil is forced
into the bearings, eventually leading to bearing
failure, while at high speeds,
excessive amounts of oil may be lost from the bearings
and compressor and potentially into the discharge
line due to splashing.
Eventually the oil runs out and the bearings are left unlubricated, again
leading to failure, and the oil may contaminate the refrigerant, air or other
working gas.
Gas compressors are used in various applications where either higher pressures or lower volumes of gas are needed:
·
In pipeline transport of purified natural gas
·
Petroleum refineries, natural gas processing plants,
petrochemical and chemical plants
·
Refrigeration and air conditioner, submarines, turbo
chargers and super chargers
·
Gas turbine systems and jet engines, turbojets and turbofans
·
In SCUBA diving, hyperbaric oxygen therapy, and
other life support devices
- Types :
The two main types of compressors are
dynamic and positive displacement. The positive displacement compressor is
probably the one you’re familiar with. It traps gas in a volume and then
decreases that volume. The decrease in volume causes a rise in pressure.
- Positive displacement
compressors :- A positive displacement compressor is the system which
compresses the air by the displacement of a mechanical linkage reducing the
volume (since the reduction in volume due to a piston in thermodynamics is
considered as positive displacement of the piston). Positive displacement
compressor is one which operates by drawing in a discrete volume of gas from its inlet then forcing
that gas to exit via the compressor’s outlet. The increase in the pressure of the gas is due, at least in part, to the
compressor pumping it at a mass flow rate which cannot pass through the outlet
at the lower pressure and density of the inlet.
1) Reciprocating compressors :
This type of compressor can compress
a wide range of gases, including refrigerant, hydrogen, and natural gas.
Because of this, it finds use in a wide range of applications in many different
industries and can be designed to a wide range of capacities, by varying size,
number of cylinder and cylinder unloading. 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, and more costly than
comparable rotary units. Another type of reciprocating compressor, usually employed in automotive cabin air conditioning systems, is the swash plate
or wobble plate compressor, which uses pistons moved by a swash plate mounted
on a shaft.
Reciprocating compressor
Single acting compressor
2)
Rotary
compressors :
A positive-displacement machine in
which compression of the fluid is effected directly by a rotor and without the
usual piston, connecting rod, and crank mechanism of the reciprocating
compressor. Rotary compressors have a number of features in common even though
there are differences in construction. Unlike reciprocating compressors, rotary
compressors do not use valves to move the gas through the machine. When
compared to a reciprocating compressors with rotary compressors, are lighter in
weight, experience less vibration, do not require heavy foundations. Rotary
compressors physical design varies widely. Both single- and multiple-rotor
construction are used. The design of the rotor is the main item that
distinguishes the different types of rotary compressors.
Rotary compressor
Rotary lobe compressor Rotary screw compresso
Liquid ring compressor
 Vane Compressor |
|||
|
Air bubble compressor, also known as a trompe. A mixture of air and water generated through turbulence is allowed to
fall into a subterranean chamber where the air separates from the water.
The weight of falling
water compresses the air in the top of the chamber. A submerged outlet from the
chamber allows water to flow to the surface at a lower height than the intake.
An outlet in the roof of the chamber supplies the compressed air to the
surface. A facility on this principle was built on the Montreal
River at Ragged
Shutes near Cobalt, Ontario in 1910 and supplied 5,000
horsepower to nearby mines.
1) Centrifugal compressor :
Centrifugal compressors use a 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.
:-Centrifugal compressor
2) Axial compressor :
Axial compressors are dynamic rotating compressors that use arrays of fan-like airfoils to progressively compress a fluid. They are used where high flow rates or a compact design are required. 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 compressors are used in medium to large gas turbine engines, natural gas pumping stations, and some chemical plants.
- Compressor in the industries :
There are many
options for the motor that powers the compressor that are used in industries :
·
Gas turbines, power
the axial and centrifugal flow compressors that are part of jetengines.
·
In automobiles and other types of
vehicles (including piston-powered airplanes, boats, trucks, etc.), diesel or
gasoline engines power output can be increased by compressing the intake air,
so that more fuel can be burned per cycle. These engines can power compressors
using their own crankshaft power (this setup known as a supercharger), or, use
their exhaust gas to drive a turbine connected to the compressor (this setup
known as a turbocharger).
Compressor in automobile industries
- References :
- Wikipedia
- YouTube
- Chemical engineering world
- Appalachian (Refrigeration,heating & Cooling)
Here is the link
to the animation video of compressor
Written by
Comments
Post a Comment