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ACTIVE LEARNING PROCESS. Branch: Computer Engineering. Guided By : Prof. C.H.Solanki. Prepared By :. 1 ) Amey Pradhan - 13BECEG061 Patel Ami - 13BECEN062 Keyur Rana - 13BECEGO63. INTRODUCTION.
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ACTIVE LEARNING PROCESS Branch: Computer Engineering Guided By : Prof. C.H.Solanki Prepared By : 1) AmeyPradhan - 13BECEG061 Patel Ami - 13BECEN062 KeyurRana - 13BECEGO63
INTRODUCTION • The machine which takes in air or any other gas at low pressure and compresses it to high pressure are called compressors. • They are power consuming machines in which mechanical work is converted into the pressure head of air or gas. They are also considered as reversed heat engine. • A compressor is used for increasing the pressure of air is called air compressor.
CLASSIFICATION OF COMPRESSORS 1. Method of compression a) Reciprocating compressor b) Rotary compression c) Centrifugal compressor 2. Delivery pressure 3. Principle of operation a) Positive displacement b) Rotodynamic or steady flow compressor 4. The number of stages 5. The number of cylinders 6. The pressure limit 7. Volume of air delivered 8. Fluid to be compressed
USES OF COMPRESSED AIR • In refrigeration cycle. • Operating pneumatic tools like drill, hammers,riveting machine etc. • Filling the air in automobile tyres. • Spray painting. • Increasing inlet pressure of I.C. engines. • To operate air motor in mines where fire risks are more. • Pumping of water. • Gas turbine power plant. • Conveying the materials like sand and concrete along the pipe line. • For sand blasting. • Operating blast furnaces. • Operating air brakes used in buses,trucks,trains,etc.
ROTODYNAMIC COMPRESSORS • Centrifugal compressors- arrangement is similar to centrifugal pump. It consists of a rotating element called impeller and a volute casing. Impeller rotates about 30,000RPM. The air enters into the compressor through the suction eye of the impeller. Due to the rotation of the impeller at a high speed produces centrifugal force which causes the air to move out of the impeller at a high velocity. Then the air with high velocity enters into a diffuser ring. The diffuser blades of the diffuser ring are so shaped that these provide an increased area of passage to the air which is passing outwards due to which the velocity of air leaving the impeller is reduced and its pressure is increased. The high pressure air then flows to the divergent passage of volute casing. The velocity of air is further reduced due to increased cross sectional area of volute casing causing very small rise in pressure. From the casing the compressed air leads to exit pipe and finally comes out of the compressor.
This type of compressor is a continuous flow machine suitable for large flow rate at moderate pressure. The pressure ratios between 4 to 6 may be obtained in this type of compressor. Pressure ratio upto 12 can be obtained by multistage centrifugal compressors.
2) Axial flow compressor- In this compressor air flows parallel to the axis of compressor, hence it is known as axial flow compressor. It consists of a casing fitted with several rows of fixed blades and rotor attached with several rows of moving blades. The fixed and moving blades are placed on alternate rows. The function of the fixed blades is to receive the high velocity air from the moving blades. When the air passes through fixed blades they reduce velocity and increases the pressure, also directs the flow to next row of moving blades. The basic working principle of this compressor is same as that of the centrifugal compressor. Moving blades can be approx. as impeller and fixed blades can be diffuser ring as incase of centrifugal compressor.
Axial flow compressor is also a high speed machine and speed may even vary from 10,000 to 30,000 RPM. Pressure ratio of 10:1 can be achieved. it is generally used in aircraft and gas turbine plants.
POSITIVE DISPLACEMENT COMPRESSORS • Roots blowers- Theroots blower consists of two lobes. For higher pressure ratio, three and four lobes may be used. Here the pressure of air delivered is slightly above the atmosphere. The machine consists of a fixed casing which contains two shafts fitted with two lobe rotors. One of the rotor is driven by electric motor or other prime movers and other is driven in opposite directions. The profile of the rotor is of cycloidal or involute type. The air is drawn through the inlet pipe due to rotation of the rotors. The volume of air is entrapped between one rotor and casing for a very short interval. Due to rotation of lobes trapped air is carried to the discharge side. Continued rotation of rotors, opens the trapped space to the discharge port. The air pushed to the reciever due to the continued rotation of rotors.
2) Vane type compressor or blower- This type of compressor consists of rotor drum mounted eccentrically in the cylindrical casing. The rotor is provided with vanes in the slots. These vanes or blades are made from non-metallic material usually fibre or carbon. The vanes remain in contact with the wall of casing due to centrifugal force or spring force or both. The vanes can slide in and out in the slots. The volume between two vanes keeps on changing due to eccentric motion of the rotor. The rotation of the rotor causes space to be created between the vanes, thrrotorand casing. This space is connected to suction pipe so that air enters into the created space and filled it.
A volume V1 of air is trapped between the vanes and casing. With the rotation of rotor, air gets compressed due to reduction of space towards delivery side. The fluid volume reduces to V2, when it communicates with the delivery side. Since the receiver pressure is higher than the compressed air between the vanes, the back flow of air from the receiver will take place. It causes further rise in pressure of the internally compressed air until the pressure equalizes. Due to rotation of vanes air is delivered to the receiver. In this type of compressor, the total pressure rise is partially due to internal compression between the vanes and partially due to back flow of air from receiver. This type of compressor can produce a pressure ratio upto 6 per stage.
Comparison between Reciprocating and Rotodynamic compressors • Reciprocating compressor • Maximum delivery pressure can be achieved as high as 1000 bar. • These are suitable for low discharge and high pressure applications. • Rotational speed is low. • Air discharge is not continuous, so a receiver is needed. • These compressors require complicated lubrication system. • Size of this compressor is larger than rotary compressor for same discharge. • Due to reciprocating parts balancing is the major problem. • Maintenance cost is more. • Due to clerance, volumetric efficiency is less than 100% • Running cost is more. • Rotodynamic compressor • Maximum delivery pressure is upto 10 bar however, by multistaging up to 40 bar delivery pressure may be achieved. • These are suitable for high discharge low pressure applications. • Rotational speed is high upto 30,000RPM. • Air discharge is continuous, so a receiver is not needed. • Simple lubrication system is required. • Size of this compressor is smaller than reciprocating compressor for same discharge. • There is no reciprocating parts, balancing is not problem. • Maintenance cost is less. • There is no clearance so volumetric efficiency is nearly 100% • Running cost is less.
