GANDHINAGAR INSTITUTE OF TECHNOLOGY

ACTIVE LEARNING ASSIGNMENTELEMENTS OF MECHANICAL ENGINEERING(2110006)

AIR COMPRESSORSPREPARED BY: GUIDED BY:

Ravi Gelani (150120116020) PROF. Jyotin Kateshia Kaushik Nakrani (150120116039)Shrvan Kushwaha (150120116034)

BRANCH: INFORMATION TECHNOLOGY- D-D2SEMESTER:2 (EVEN)

GOALS:IntroductionClassificationTerminologyReciprocating compressorCentrifugal compressorAxial compressorReferences

AIR COMPRESSORS• An air compressor is a device that converts

power into potential energy by forcing air into a smaller volume and thus increasing its pressure.

• The energy in the compressed air can be stored while the air remains pressurized.

CLASSIFICATION:Air Compressors are classified on various categories, according to the: Principle of Working:1. Positive displacement2. Dynamic(Negative displacement)

Number of Stages:1. Single stage - pressure ratio upto 5 – 6.2. Multi stage – pressure ratio more than 6.

Acting of Piston:1. Single Acting 2. Double Acting

Number of Cylinders:1. Single Cylinder 2. Double Cylinder

Pressure Ratio:1. Fan- pressure ratio upto 1.12. Blower- pressure ratio 1.1 to 2.53. Compressor- pressure ratio more than 2.5

Method of Cooling:1. Air cooled 2. Water cooled

According to the Arrangement of Cylinder:1. Vertical 3. V-type2. Horizontal 4. Radial

AIR COMPRESSOR TERMINOLOGY SINGLE ACTING COMPRESSOR:Compressor in which suction, compression and delivery of air takes place only in one side of piston.

DOUBLE ACTING COMPRESSOR:Compressor in which suction, compression and delivery of air takes place on both sides of piston.

SINGLE STAGE COMPRESSOR:Compressor in which compression of air from suction pressure to delivery pressure takes place in one cylinder .

MULTI STAGE CYLINDER:Compressors in which compression of air from suction pressure to delivery pressure takes place in more than one cylinder.

COMPRESSION RATIO:It is defined as a ratio of an absolute discharge pressure to absolute suction pressure.

VOLUMETRIC EFFICIENCY:Defined as the ratio of actual volume of air taken in the compressor to the swept volume of the compressor.

COMPRESSOR CAPACITY:Volume of the air delivered by the compressor.Expressed in cubic metre per minute or cubic metre per second.

RECIPROCATING COMPRESSORS

• A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure

• The intake gas enters the suction manifold, then flows into the compression cylinder where it gets compressed by a piston driven in a reciprocating motion via a crankshaft, and is then discharged.

• It also consists of inlet valve and delivery valve and they operated because of the pressure difference across it.

RECIPROCATING AIR COMPRESSOR

Working:• When piston moves downward during suction stroke, the

compressed air left in the cylinder expands and due to expansion, the pressure inside the cylinder falls below atmospheric pressure which result in the opening of inlet valve opens and delivery valve remains closed and fresh air is sucked into the cylinder.

• At the time of upward stroke, there is slight increase in pressure which closes the inlet valve and when both the valves are closed the pressure inside the valve increases.

• So when the pressure inside the cylinder increases above the compressed air pressure on outside of delivery valve,the delivery valve remain open and compressed air is delivered into the receiver. So, at the end piston move downward and as pressure decreases delivery valve remain closed.

• When pressure falls below atmospheric once again inlet valve opens and thus the cycle is repeated.

Application:

•  Applications include oil refineries, gas pipelines, chemical plants, natural gas processing plants and refrigeration plants. One specialty application is the blowing of plastic bottles made of polyethylene terephthalate (PET).

CENTRIFUGAL COMPRESSORS• Centrifugal compressors, sometimes termed radial

compressors, are a sub class of dynamic symmetric axis turbo-machinery.

• This compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller.

• It consists of an impeller (rotor) usually rotates at high speed (sometimes at 20 K to 30 K rpm) in an air tight volute casing.

• It is a steady flow of device having continuous flow of air and it deals with the large quantity of air with the moderate range.

CENTRIFUGAL COMPRESSOR

AXIAL COMPRESSOR• An axial compressor is a machine that can continuously pressurise

gases. • It is a rotating, airfoil-based compressor in which the gas or

working fluid principally flows parallel to the axis of rotation. • This differs from other rotating compressors such as centrifugal

compressors, axi-centrifugal compressors and mixed-flow compressors where the fluid flow will include a "radial component" through the compressor.

• The energy level of the fluid increases as it flows through the compressor due to the action of the rotor blades which exert a torque on the fluid.

• The stationary blades slow the fluid, converting the circumferential component of flow into pressure. Compressors are typically driven by an electric motor or a steam or a gas turbine.

• Axial flow compressors produce a continuous flow of compressed gas, and have the benefits of high efficiency and large mass flow rate, particularly in relation to their size and cross-section.

• They do, however, require several rows of airfoils to achieve a large pressure rise, making them complex and expensive relative to other designs (e.g. centrifugal compressors).

Working:• Axial compressors consist of rotating and stationary components.

A shaft drives a central drum, retained by bearings, which has a number of annular airfoil rows attached usually in pairs, one rotating and one stationary attached to a stationary tubular casing.

• A pair of rotating and stationary airfoils is called a stage. The rotating airfoils, also known as blades or rotors, accelerate the fluid. The stationary airfoils, also known as stators or vanes, convert the increased rotational kinetic energy into static pressure through diffusion and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage.

•  The cross-sectional area between rotor drum and casing is reduced in the flow direction to maintain an optimum Mach number using variable geometry as the fluid is compressed.

Application:• Axial compressors are integral to the design of large gas

turbines such as jet engines, high speed ship engines, and small scale power stations. They are also used in industrial applications such as large volume air separation plants,blast furnace air, fluid catalytic cracking air.

• Due to high performance, high reliability and flexible operation during the flight envelope, they are also used in aerospace engines.

References:• Elements of Mechanical Engineering by “N M Bhatt” & “Dr. J

R Mehta”.• Physics textbook of 12th of the “Frank Brothers”.s• Internet : www.compressor.com

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