THERMAL ENGINEERING. SHIBIN MOHAMED Asst. Professor Dept. of Mechanical Engineering Al Ameen Engineering College.

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1 THERMAL ENGINEERING SHIBIN MOHAMED Asst. Professor Dept. of Mechanical Engineering Al Ameen Engineering College Al- Ameen Engg. College 1

2 Steam Engine: Definition A steam engine is a heat engine that converts steam energy into mechanical motion. Steam may be produced by combustion or no-combustion heat sources. Combustion heat sources include: Hydrocarbon (Oil, Gas and Coal), Biomass. Non-combustion heat sources include: Solar, Nuclear or Geothermal. Al- Ameen Engg. College 2 2

3 Evolution of Steam Engines 2010 Steam Turbine 100 BC: the Aeolpile 1551 Taqi al-din 1629 Giovanni Branca Al- Ameen Engg. College 3 3

4 History of Steam Engine Inventors used experimental devices, such as the rudimentary steam turbine device described by Taqi al-din in 1551 and Giovanni Branca in 1629, to demonstrate the properties of steam. The first practical steam-powered 'engine' was a water pump, developed in 1698 by Thomas Savery. It proved only to have a limited lift height and was prone to boiler explosions, but it still received some use for mines and pumping stations. The first commercially successful engine, the atmospheric engine, invented by Thomas Newcomen did not appear until Newcomen's engine was relatively inefficient, and in most cases was only used for pumping water. Al- Ameen Engg. College 4

5 History of Steam Engine James Watt developed an improved version of Newcomen's engine between 1763 and 1775 which used 75% less coal than Newcomen's, and was hence much cheaper to run. Watt proceeded to develop his engine further, modifying it to provide a rotary motion suitable for driving factory machinery. Early engines were "atmospheric", meaning that they were powered by the vacuum generated by condensing steam instead of the pressure of expanding steam. Cylinders had to be large, as the only usable force acting on them was atmospheric pressure. Steam was only used to compensate for the atmosphere allowing the piston to move back to its starting position. Even if pressured steam had been available, it could not do any work (push) against the chain connecting the piston to the beam. Al- Ameen Engg. College 5

6 100 BC: Aeolipile-The First Steam Engine Al- Ameen Engg. College 6 An aeolipile (or aeolipyle, or eolipile), also known as a Hero engine, is a simple bladeless radial steam turbine which spins when the central water container is heated. Torque is produced by steam jets exiting the turbine, much like a tip jet or rocket engine. The device was described by Hero of Alexandria dating back to the 1 st Century A.D.

7 1551: Taqi al-din Steam Engine Al- Ameen Engg. College 7 One of these methods is to have at the end of the spit a wheel with vanes, Opposite the wheel place a hollow pitcher made of copper with a closed head and full of water. The nozzle of the pitcher is placed opposite the vanes of the wheel. Kindle fire under the pitcher and steam will exit from its nozzle in a restricted form and it will turn the vane wheel. When the pitcher becomes empty of water bring close to it cold water in a basin and let the nozzle of the pitcher dip into the cold water. The heat will cause all the water in the basin to be attracted into the pitcher and the [the steam] will start rotating the vane wheel again. 7

8 1629: Branca s In 1629 an Italian engineer, Giovanni Branca, described a stamping mill. A jet nozzle directed steam onto a horizontally mounted turbine wheel, which then turned an arrangement of gears that operated the stamping mill. Al- Ameen Engg. College 8 8

9 1687: Newton s Wagon Newton attempted to put his newly formulated laws of motion to the test. He tried to propel a wagon by directing steam through a nozzle pointed rearward Steam was produced by a boiler mounted on the wagon. Due to lack of power from the steam, this vehicle didn't operate. But he conceived moving engine Al- Ameen Engg. College 9 9

10 1698: Savery Engine Water above the boiling point produces steam at a pressure greater than one atmosphere. If valves A and B are open but C and D closed, then the steam pressure can pump water to height h2. When the cylinder is full of steam, then valves A and B can be closed and D opened. If cooling water is supplied to the cylinder, then the steam will condense, precipitously dropping its vapour pressure. The resulting vacuum causes water to rise height h1 from the mine shaft provided that height is less than 34 ft. The process can be repeated to pump water from the mine. Al- Ameen Engg. College 10

11 1698: Savery Engine Al- Ameen Engg. College 11

12 1712: Newcomen Engine A piston in a cylinder is connected to a rocker arm attached to a pump. first the cylinder was filled with steam from a boiler. This pushed the piston up. Then water was sprayed into the cylinder creating a vacuum. This pushed the piston down pulling the pump rod on the other side of the rocker arm up, thus lifting the water. The opening and closing of valves for the alternating injection of steam and water was self-actuating so the engine and pump could operate continuously. Al- Ameen Engg. College 12

13 1765: Watt Engine The Newcomen system of alternately sending jets of steam, then cold water into the cylinder meant that the walls of the cylinder were alternately heated, then cooled at each stroke. As each charge of steam was introduced, it would continue condensing until the cylinder approached working temperature once again. So at each stroke part of the potential of the steam was lost. Watt conceived the idea of a separate condensation chamber. Watt's idea was to equip the engine with a second, small cylinder, connected to the main one. The cold water was injected only into the condensation chamber. This type of condenser is known as a jet condenser. Because the chambers were connected, this caused condensation without significant loss of heat. The condenser remained cold and under less atmospheric pressure than the cylinder, while the cylinder remained hot. Al- Ameen Engg. College 13

14 1765: Watt Engine Al- Ameen Engg. College 14

15 1784: Steam Engine for Locomotive (William Murdoch) Al- Ameen Engg. College 15

16 The London Steam Carriage was an early steampowered road vehicle constructed by Richard Trevithick in 1803 The world's first selfpropelled passengercarrying vehicle. Trevithick later developed a steam locomotive on rails. Al- Ameen Engg. College 16 16

17 Concept of Uniflow Steam Engine Schematic animation of a uniflow steam engine. The valves are controlled by the rotating camshaft at the top. High pressure steam enters, and exhausts. Al- Ameen Engg. College 17 17

18 STEAM TURBINES A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Sir Charles Parsons in Steam Turbine may also be define as a device which converts heat energy of to the steam to the mechanical energy which finally converted into electrical energy. Al- Ameen Engg. College 18

19 Steam Turbine Fundamentals Fundamentals Energy Transfer Coal, Natural Gas, Nuclear, Biofuel, Waste Fuel Al- Ameen Engg. College 19 19

20 WORK IN A TURBINE VISUALIZED PES Al- Ameen Engg. College 20 20

21 Simplistic Steam Turbine working principles 1-2 isentropic compression(pump) 2-3 constant pressure heat addition 3-4 isentropic expansion (turbine) 4-1 constant pressure heat rejection Al- Ameen Engg. College 21 21

22 Description of common types of Turbines. The common types of steam turbine are 1. Impulse Turbine. 2. Reaction Turbine. The main difference between these two turbines lies in the way of expanding the steam while it moves through them. PES Al- Ameen Engg. College 22 22

23 PRESSURE-VELOCITY DIAGRAM FOR A TURBINE NOZZLE PRESSURE ENTRANCE HIGH THERMAL ENERGY HIGH PRESSURE LOW VELOCITY STEAM INLET EXIT LOW THERMAL ENERGY LOW PRESSURE HIGH VELOCITY STEAM EXHAUST VELOCITY PES Al- Ameen Engg. College 23 23

24 Simple impulse Turbine. It the impulse turbine, the steam expanded within the nozzle and there is no any change in the steam pressure as it passes over the blades PES Al- Ameen Engg. College 24 24

25 IMPULSE TURBINE PRINCIPLE ROTOR NOZZLE STEAM CHEST PES Al- Ameen Engg. College 25 25

26 Reaction Turbine In this type of turbine, there is a gradual pressure drop and takes place continuously over the fixed and moving blades. The rotation of the shaft and drum, which carrying the blades is the result of both impulse and reactive force in the steam. The reaction turbine consist of a row of stationary blades and the following row of moving blades PES Al- Ameen Engg. College 26 26

27 The fixed blades act as a nozzle which are attached inside the cylinder and the moving blades are fixed with the rotor as shown in figure When the steam expands over the blades there is gradual increase in volume and decrease in pressure. But the velocity decrease in the moving blades and increases in fixed blades with change of direction. PES Al- Ameen Engg. College 27 27

28 Because of the pressure drops in each stage, the number of stages required in a reaction turbine is much greater than in a impulse turbine of same capacity. It also concluded that as the volume of steam increases at lower pressures therefore the diameter of the turbine must increase after each group of blade rings. PES Al- Ameen Engg. College 28 28

29 REACTION TURBINE PRINCIPLE ROTOR PES STEAM CHEST Al- Ameen Engg. College 29 29

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31 PES Al- Ameen Engg. College 31 31

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33 Velocity-Compounded Turbine Velocity compounding is a form of staging which by dividing the work load over several stages results in improved efficiency and a smaller diameter for the blade wheels due to a reduction in Ideal blade speed per stage. Inlet Pressure P = 1 V Inlet Velocity Al- Ameen Engg. College 33 33

34 GAS TURBINES: How they work Energy is added to the gas stream Combustion increases the temperature, velocity, and volume of the gas flow Turbine rotates, powering the compressor Energy is then extracted in the form of shaft power, compressed air and thrust Al- Ameen Engg. College 34

35 Power Generation Single Shaft Turbine Engine Output Shaft Power 3)Expansion (Turbine) 2) Combustion 1) Compression Output Shaft Power Two Shaft Turbine Engine Mechanical Drive Al- Ameen Engg. College 35 35

36 Simplistic Gas Turbines working principles 1-2 Isentropic compression (in a compressor) 2-3 Constant pressure heat addition (in a combustor) 3-4 Isentropic expansion (in a turbine) 4-1 Constant pressure heat rejection Al- Ameen Engg. College 36 36

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39 TYPES OF TURBINES A portion of the kinetic energy of the expanding gases is extracted by the turbine section, and this energy is transformed into shaft horsepower which is used to drive the compressor and accessories. In turboprop and turboshaft engines, additional turbine rotors are designed to extract all of the energy possible from the remaining gases to drive a powershaft. There are basically two types: 1) Axial flow turbine 2) Radial in flow turbine Al- Ameen Engg. College 39

40 AXIAL FLOW TURBINE This turbine is used in all gas-turbine-powered aircraft. The axial-flow turbine consists of two main elements, a set of stationary vanes followed by a turbine rotor. Axial-flow turbines may be of the single-rotor or multiple-rotor type. A stage consists of two main components: a turbine nozzle and a turbine rotor or wheel. Turbine blades are of two basic types, the impulse and the reaction. Modern aircraft gas turbines use blades that have both impulse and reaction sections. Al- Ameen Engg. College 40 alks..org

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42 RADIAL INFLOW TURBINE Al- Ameen Engg. College 42

43 RADIAL INFLOW TURBINE The radial inflow turbine has the advantage of ruggedness and simplicity, and it is relatively inexpensive and easy to manufacture when compared to the axial-flow turbine. The radial flow turbine is similar in design and construction to the centrifugal-flow compressor. Radial turbine wheels used for small engines are well suited for a higher range of specific speeds and work at relatively high efficiency. Al- Ameen Engg. College 43

44 Advantages of gas turbine engines Very high power-to-weight ratio More size efficient Moves in one direction only, with fewer moving parts Low operating pressures High operation speeds Low lubricating oil cost and consumption Al- Ameen Engg. College 44

45 Disadvantages of gas turbine engines More expensive compared to a similar-sized reciprocating engine More complex machining operations Usually less efficient than reciprocating engines, especially at idle Delayed response to changes in power settings Al- Ameen Engg. College 45

46 HYDRAULIC TURBINES: How they work? Hydraulic Turbines have a row of blades fitted to the rotating shaft or a rotating plate. Flowing liquid, mostly water, when pass through the Hydraulic Turbine it strikes the blades of the turbine and makes the shaft rotate. While flowing through the Hydraulic Turbine the velocity and pressure of the liquid reduce, these result in the development of torque and rotation of the turbine shaft. Large modern water turbines operate at mechanical efficiencies greater than 90%. Al- Ameen Engg. College 46

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48 HYDRAULIC TURBINES : Classification Classification of Hydraulic Turbines: 1. Based on flow path a) Axial Flow Hydraulic Turbines b) Radial Flow Hydraulic Turbines c) Mixed Flow Hydraulic Turbines 2. Based on pressure change a) Impulse Turbine b) Reaction Turbine 3. Based on working principle a) The Pelton Turbine b) The Kaplan Turbine c) The Francis Turbine Al- Ameen Engg. College 48

49 BASED ON FLOW PATH : Axial Flow : These Turbines has the flow path of the liquid mainly parallel to the axis of rotation. Eg: Kaplan Turbines. Radial Flow : Such Hydraulic Turbines has the liquid flowing mainly in a plane perpendicular to the axis of rotation. Eg: Old Francis Turbine Mixed Flow : These Turbines has a significant component of both axial and radial flows. Such types of Hydraulic Turbines are called as Mixed Flow Turbines. Eg: New Francis Turbine is an example of mixed flow type, in Francis Turbine water enters in radial direction and exits in axial direction. Al- Ameen Engg. College 49

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51 BASED ON PRESSURE CHANGE: Impulse Turbine : The pressure of liquid does not change while flowing through the rotor of the machine. In Impulse Turbines pressure change occur only in the nozzles of the machine. Eg: Pelton Wheel. Reaction Turbine : The pressure of liquid changes while it flows through the rotor of the machine. The change in fluid velocity and reduction in its pressure causes a reaction on the turbine blades; this is where from the name Reaction Turbine may have been derived. Eg: Francis and Kaplan Turbines Al- Ameen Engg. College 51

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53 BASED ON WORKING PRINCIPLE: PELTON Turbine (For High Heads) The high speed water jets emerging form the nozzles strike the buckets at splitters, placed at the middle of a bucket, from where jets are divided into two equal streams. These stream flow along the inner curve of the bucket and leave it in the direction opposite to that of incoming jet. The high speed water jets running the Pelton Wheel Turbine are obtained by expanding the high pressure water from any water body situated at some height through nozzles to the atmospheric pressure. The change in momentum of water stream produces an impulse on the blades of the wheel of Pelton Turbine. This impulse generates the torque and rotation in the shaft of Al- Ameen Engg. College 53 Pelton Turbine

54 BASED ON WORKING PRINCIPLE: FRANCIS Turbine (For Low to Medium Heads) Francis Turbines are generally installed with their axis vertical. Water with high head (pressure) enters the turbine through the spiral casing surrounding the guide vanes. The water looses a part of its pressure in the volute (spiral casing) to maintain its speed. Then water passes through guide vanes where it is directed to strike the blades on the runner at optimum angles. As the water flows through the runner its pressure and angular momentum reduces. This reduction imparts reaction on the runner and power is transferred to the turbine shaft. Al- Ameen Engg. College 54

55 BASED ON WORKING PRINCIPLE: KAPLAN Turbine : (for a wide range of heads) The water enters the turbine through the guide vanes which are aligned such as to give the flow a suitable degree of swirl. The flow from guide vanes pass through the curved passage which forces the radial flow to axial direction in the form of free vortex. The axial flow of water with a component of swirl applies force on the blades of the rotor and looses its momentum. This produces torque and rotation (their product is power) in the shaft. Al- Ameen Engg. College 55

56 PRINCIPLE OF TURBOMACHINERY OPEN-(WINDMILL, FAN, PROPELLER); CLOSED-(TURBINES, COMPRESSOR, PUMP) Turbomachinery, in mechanical engineering, describes machines that transfer energy between a rotor and a fluid, including both turbines and compressors. While a turbine transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid. Centrifugal pumps are also turbomachines that transfer energy from a rotor to a fluid, usually a liquid, while turbines and compressors usually work with a gas. Al- Ameen Engg. College 56

57 CENTRIFUGAL PUMP Al- Ameen Engg. College 57

58 COMPRESSORS & TURBINES Al- Ameen Engg. College 58

59 PRINCIPLE OF TURBOMACHINERY Any devices that extracts energy from or imparts energy to a continuously moving stream of fluid (liquid or gas) can be called a Turbomachine. A turbomachine is a power or head generating machine which employs the dynamic action of a rotating element, the rotor; The action of the rotor changes the energy level of the continuously flowing fluid through the machine. Turbines, compressors and fans are all members of this family of machines. Al- Ameen Engg. College 59

60 HISTORY OF IC ENGINES Al- Ameen Engg. College 60

61 In an Internal combustion engine, combustion takes place within working fluid of the engine, thus fluid gets contaminated with combustion products. Petrol engine is an example of internal combustion engine, where the working fluid is a mixture of air and fuel. In an External combustion engine, working fluid gets energy using boilers by burning fossil fuels or any other fuel, thus the working fluid does not come in contact with combustion products. Steam engine is an example of external combustion engine, where the working fluid is steam. Al- Ameen Engg. College 61

62 HISTORY OF IC ENGINES 1700s -Steam engines (external combustion engines) Lenoir engine (η = 5%) Otto-Langen engine (η= 12%, 90 RPM max.) Otto four stroke spark ignition engine (η= 14%, 160 RPM max.) 1880s -Two stroke engine Diesel four stroke compression ignition engine Al- Ameen Engg. College Wankel rotary engine ne ww ww.edutalks.org

63 STEAM ENGINES Al- Ameen Engg. College 63

64 LENOIR ENGINES Two-stroke engine which burnt a mixture of coal gas and air Al- Ameen Engg. College 64

65 OTTO-LANGEN VERTICAL ENGINES Explosive Combustion Al- Ameen Engg. College 65

66 OTTO- 4 STROKE ENGINES Progressive Controlled Combustion Al- Ameen Engg. College 66

67 TWO STROKE ENGINES (Sir Dugald Clerk) Al- Ameen Engg. College 67

68 DIESEL ENGINES (Rudolph Diesel) Al- Ameen Engg. College 68

69 THE EARLY LOCOMOTIVES Al- Ameen Engg. College 69

70 INTERNAL COMBUSTION ENGINES- WORKING PRINCIPLE Al- Ameen Engg. College 70

71 Internal combustion engines may be classified as : Spark Ignition engines. Compression Ignition engines. Spark ignition engine (SI engine): An engine in which the combustion process in each cycle is started by use of an external spark. Compression ignition engine (CI engine): An engine in which the combustion process starts when the air-fuel mixture self ignites due to high temperature in the combustion chamber caused by high compression. Spark ignition and Compression Ignition engine operate on either a four stroke cycle or a two stroke cycle. Al- Ameen Engg. College 71

72 BASIC ENGINE NOMENCLATURE Al- Ameen Engg. College 72

73 Four stroke cycle : It has four piston strokes over two revolutions for each cycle. o revolutions for each cycle. Al- Ameen Engg. College 73

74 Al- Ameen Engg. College 74 4 STROKE PETROL ENGINE (SI)

75 Four strokes of SI Engine Cycle : Suction/Intake stroke: Intake of air fuel mixture in cylinder through intake manifold. The piston travel from TDC to BDC with the intake valve open and exhaust valve closed. This creates an increasing volume in the combustion chamber, which in turns creates a vacuum. The resulting pressure differential through the intake system from atmospheric pressure on the outside to the vacuum on the inside causes air to be pushed into the cylinder. As the air passes through the intake system fuel is added to it in the desired amount by means of fuel injectors or a carburettor. Al- Ameen Engg. College 75

76 Compression stroke: When the piston reaches BDC, the intake valve closes and the piston travels back to TDC with all valves closed. This compresses air fuel mixture, raising both the pressure and temperature in the cylinder. Near the end of the compression stroke the spark plug is fired and the combustion is initiated. Al- Ameen Engg. College 76

77 Combustion of the air-fuel mixture occurs in a very short but finite length of time with the piston near TDC (i.e., nearly constant volume combustion). It starts near the end of the compression stroke slightly before TDC and lasts into the power stroke slightly after TDC. Combustion changes the composition of the gas mixture to that of exhaust products and increases the temperature in the cylinder to a high value. This in turn increases the pressure in the cylinder to a high value. Al- Ameen Engg. College 77

78 Expansion stroke/power stroke : With all valves closed the high pressure created by the combustion process pushes the piston away from the TDC. This is the stroke which produces work output of the engine cycle. As the piston travels from TDC to BDC, cylinder volume is increased, causing pressure and temperature to drop. Al- Ameen Engg. College 78

79 Exhaust stroke: By the time piston reaches BDC, the cylinder is still full of exhaust gases at approximately atmospheric pressure. With the exhaust valve open the piston travels from BDC to TDC in the exhaust stroke. This pushes most of the exhaust gases out of the cylinder into the exhaust system at about atmospheric pressure, leaving only that trapped in the clearance volume when the piston reaches TDC. Al- Ameen Engg. College 79

80 Al- Ameen Engg. College 80 4 STROKE DIESEL ENGINE (CI)

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82 Four strokes of CI Engine Cycle : Intake/Suction Stroke : The same as the intake stroke in an SI engine with one major difference : no fuel is added to the incoming air, Compression Stroke : The same as in an SI engine except that only air is compressed and compression is to higher pressures and temperature Late in the compression stroke fuel is injected directly into the combustion chamber, where it mixes with very hot air. This causes the fuel to evaporate and self ignite, causing combustion to start.» Combustion is fully developed by TDC and continues at about constant pressure until fuel injection is complete and Al- Ameen Engg. College 82 the piston has started towards BDC

83 Expansion/Power stroke : The power stroke continues as combustion ends and the piston travels towards BDC Exhaust stroke : Same as with an SI engine Al- Ameen Engg. College 83

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85 Two stroke cycle : It has two piston strokes over one revolution for each cycle. Al- Ameen Engg. College 85

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88 COMPRESSORS Type of compressor Positive displacement Dynamic Reciprocating Rotary Centrifugal Axial Al- Ameen Engg. College 88

89 How Compressors Works Individual gas always travel at high speed, at normal temperature, they strike against the walls of an enclosing vessel and produce what is known as pressure. If the enclosing vessel is fitted with a piston the gas can be squeezed into a smaller space & the molecule travel could be restricted. The molecules then hit the walls with greater frequency increasing the pressure. The moving piston also delivers energy to the molecules, causing them to move with increased velocity. Furthermore, all the molecules have been forced into a smaller space, which results in an increased number of collisions on a unit area of wall. This, together with increased molecules velocity results Al- Ameen in Engg. increased College 89 pressure. re.

90 Major Design Classification There are 2 major design classification of compressor: 1. Positive displacement 2. Dynamic Al- Ameen Engg. College 90

91 1. Positive Displacement Compressors In positive displacement compressor, successive volumes of air are confined within a closed space. Pressure is increased by reducing volume of space. Two types of positive displacement compressors: 1. Reciprocating 2. Rotary Al- Ameen Engg. College 91

92 Reciprocating Compressor single acting Al- Ameen Engg. College 92

93 Reciprocating Compressor double acting Al- Ameen Engg. College 93

94 Rotary Compressor Al- Ameen Engg. College 94

95 Rotary Compressor Sliding vane Rotary Compressor Al- Ameen Engg. College 95 utalks.org

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97 Rotary Compressor Two Impeller Rotary Compressor Al- Ameen Engg. College 97

98 Rotary Compressor Liquid Piston type Rotary Compressor Al- Ameen Engg. College 98

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100 Rotary Compressor Screw Type Rotary Compressor Al- Ameen Engg. College 100

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102 2. Dynamic Compressors Dynamics compressors use rotating elements to accelerate the gas by diffusing action, velocity is converted to static pressure. Total energy in a flowing gas stream is constant. Entering an enlarged section, flow speed is reduced and some of the velocity energy turns into pressure energy. Thus, static pressure is higher in the enlarged section. Two types of dynamic compressors: 1. Centrifugal Compressors 2. Axial Compressors Al- Ameen Engg. College 102

103 Dynamic Compressors - Centrifugal Open impeller is used in single stage compressors to produce high head with but small flow (capacity). Al- Ameen Engg. College 103

104 Dynamic Compressors - Centrifugal Semi-enclosed impeller is used in single staged compressors or in the first stage of multi-stage compressors to produce a large flow Al- Ameen Engg. College 104

105 Dynamic Compressors - Centrifugal The enclosed impeller is used in multi-stage compressors where pressure is increased in to a high discharge pressure Al- Ameen Engg. College 105 w.edutalks.org

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107 Dynamic Compressors-Axial In axial flow compressors, gas moves generally parallel to the shaft axis. The axial compressor or blower is a dynamic type of machine, identified by the use of moving and stationary blading to accomplish the velocity-pressure conversion This means that half of the pressure rise is accomplished in the rotor blade and half in the stator blade (50%reaction principle). As gas flows through the rotating blades, pressure and velocity both increase Each row of stationary blades converts the energy of the increased velocity to additional pressure, acting as a diffuser for the gas flowing out of the preceding row of rotating blades. Also, the stationary blades act as nozzle to guide the gas into the next row of rotating blades. Each stage consists, therefore, of one rotating and one stationary row of blading. Al- Ameen Engg. College 107

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