Elements of Mechanical Engineering PDF

Elements of Mechanical Engineering Prof. Mohsin J. Dadi, Assistant Professor Department of Mechanical Engineering  CHAPTER-5 Energy Conversion Devices Introduction to Steam Generator Steam Generator  Steam boiler may be defined as “A closed pressure vessel in which steam is generat...

Elements of Mechanical Engineering Prof. Mohsin J. Dadi, Assistant Professor Department of Mechanical Engineering  CHAPTER-5 Energy Conversion Devices Introduction to Steam Generator Steam Generator  Steam boiler may be defined as “A closed pressure vessel in which steam is generated with capacity exceeding 25 liters, gauge pressure greater than or equal to 1 kg/cm2, and water Is heated at 100 °C or above. Application  For generating power in steam Engine or steam turbines.  At low pressures for industrial process work in cotton mills, sugar factories, etc.  For producing hot water for supply of hot water and for heating the buildings in cold weather. Classification of Steam Boilers  According to relative position of water and hot gases : Fire Tube and Water Tube.  According to the axis of the shell : Vertical, Horizontal and Inclined.  According to the method of firing : Internally and Externally Fired.  According to the Method of Water circulation : Natural and Forced.  According to the Pressure of steam : Low, Medium and High Pressure.  According to the mobility of boiler : Stationary and Mobile.  According to the number of tubes in the boiler : Single Tube and Multi Tube. General Terms in Steam Boilers  Cylindrical Shell: It is made up of steel plates bent into cylindrical form and rewetted and welded together.  Combustion Chamber : It is the space, generally below the boiler shell, meant for burning fuel in order to produce steam from the water contained in the shell.  Grate : It is a platform, in the combustion chamber, upon which fuel is burnt.  Furnace : It is a chamber formed by the space above grate and bellows the boiler shell in which combustion take place.  Fire hole : It is the hole through which coal is added to the furnace. General Terms in Steam Boilers  Ash Pit : It is the area in which the ash of burnt coal is collected.  Smoke Chamber : The waste gases are collected here and then releases to the chimney and then to atmosphere.  Man Hole : It is a hole provided on to the boiler shell so that a workman can go inside the boiler for inspection/  Mud Box : It collects all impurities present in the water. It is at the bottom of the barrel or shell/  Hand Holes : It is a hole provided on the shell to give to give east access for the purpose of cleaning the water tubes or some other internal parts of boiler. Steam Boilers Cochran Babcock Lancashire Boiler and Wilcox Locomotiv e Cochran Boiler Characteristics  Vertical  Multi Tube  Fire Tube  Internally Fired Cochran Boiler  Natural Circulation Image source : Mechanical Notes Babcock and Wilcox Boiler Characteristics  Horizontal  Multi Tube  Water Tube  Externally Fired  Natural Circulation Babcock and Wilcox Boiler Image source : Mechanical Booster Locomotive Boiler Characteristics  Horizontal  Multi Tube  Fire Tube  Internally Fired  Forced Circulation Locomotive Boiler Image source : Green-Mechanic Locomotive Boiler Locomotive Boiler Image source : Mechanical Booster Lancashire Boiler Characteristics  Horizontal  Stationary  Two Tube  Fire Tube  Internally Fired  Natural Circulation Lancashire Boiler Image source : Mech 4 Study Lancashire Boiler Lancashire Boiler Image source : Nigel Bowers Boiler Mountings  Boiler mountings are the fittings, which are necessarily mounted on the boiler itself and mandatorily required for the safe and proper operation of boiler. Various boiler mountings are,  Water Level Indicator  Pressure Gauge  Spring loaded safety valve  Fusible Plug  Blow off cock  Feed check valve  Steam stop valve etc. Water Level Indicator Function  Water level indicator is fitted outside the boiler shell to indicate the water level in the boiler through a glass tube. Water Level Indicator Image source : Mech Engineering Pressure Gauge Function  A pressure gauge is used to indicate the pressure of steam in the boiler.  It is generally mounted on the front top of the boiler.  Pressure gauge is of two types as (i) Bourdon Tube Pressure Gauge (ii) Diaphragm type pressure gauge. Pressure Gauge Image source : Learn Mechanical Spring Loaded Safety Valve Function  Spring loaded safety valve is a safely mounting fitted on the boiler shell and is essentially required on the boiler shell to safeguard the boiler against high pressure.  It is a vital part of boiler and always be in good working condition to protect the boiler from bursting under high pressure and so to save life and property. Spring Loaded Safety Valve Image source : Mechanical Engineering Fusible Plug Function  The function of fusible plug is to protect the boiler from damage due to overheating of boiler tubes by low water level. Fusible Plug Image source : Mechanical Engineering Blow Off Cock Function  It is a controllable valve opening at the bottom of water space in the boiler and is used to blow off some water from the bottom which carries mud or other sediments settled during the operation of boiler.  It is also used to completely empty the water when the boiler is shut off for cleaning purpose or for inspection and repair. Blow Off Cock Image source : Engineering enotes Feed Check Valve Function  The feed check valve is fitted in the feed water line of the boiler after the feed pump.  Its function is to allow the water to flow in the boiler when the discharge pressure of feed pump is more than the inside steam pressure of boiler and prevent the back flow in case the feed pump pressure is less than boiler pressure. Feed Check Valve Image source : Mechanical Engineering Steam Stop Valve Function  It is fitted over the boiler in between the steam space and steam supply line.  Its function is to regulate the steam supply from boiler to the steam line. Steam Stop Valve Image source : The Engineer s post Boiler Accessories  Boiler accessories are the components which are attached to the boiler (Not mounted on it) and are essentially for working of boiler and for increasing its efficiency. Various boiler accessories are,  Feed pump  Economizer  Air Preheater  Super Heater etc. Feed Pump Function  Feed pump is placed nearby the boiler and is used to feed water to boiler working at a high pressure.  The job of feed pump is not just put the water in the boiler but as boiler is working at high pressure, discharge pressure of feed pump must be sufficiently higher than this to push the water inside the boiler. Multi Stage Centrifugal Pump Image source : Learn Mechanical Economizer Function  An economizer is a specially constructed heat exchanger for harnessing the heat energy of outgoing flue gases and utilizing it in preheating of boiler feed water.  It saves the heat energy and so the fuel and decreases the operating cost of boiler by increasing its thermal efficiency. Economizer Image source : Learn Mechanical Air Preheater Function  The function of air pre-heater is to further utilize the heat of flue gases after coming out of economizer to preheat the air used in furnace or oil burner. Air Preheater (Tubular Type) Image source : ecoursesonline.iasri.res.in Introduction to Refrigeration  Refrigeration is defined as "the method of reducing the temperature of a system below surrounding temperature and maintains it at the lower temperature by continuously abstracting the heat from it.  In simple, refrigeration means the cooling or removal of heat from a system.  In refrigeration, the heat is to be removed continuously from a system or space at a lower temperature and transfer to the surrounding at a higher temperature.  In this process, according to second law of thermodynamics external work is required to convey heat from cold body to hot body. Refrigerants The refrigerant is a heat carrying medium which absorbs heat from space (desired to cool) and rejects heat to outside the refrigerator (in atmosphere). Properties of good refrigerant  High latent heat of evaporation and low specific volume.  Good thermal conductivity for rapid heat transfer.  Non-toxic, non-flammable and non-corrosive.  Low specific heat in liquid state and high specific heat in vapour state.  Low saturation pressure.  High co-efficient of performance.  Economical in initial cost and maintenance cost. Ton of refrigeration and Coefficient of performance Ton of Refrigeration  It is defined as "refrigerating effect produced by melting of 1 ton of ice from and at 0°C in 24 hours.“ OR  "Amount of heat required to remove in order to form one ton of ice in 24 hours from water at temperature 0°C". 1 ton of refrigeration = 3.5 kW. Coefficient of performance  It is defined as the ratio of refrigerating effect to work required compressing the refrigerant in the compressor. It is the reciprocal of the efficiency of a heat engine.  Thus, the value of COP is greater than unity.  Mathematically, COP = Refrigerating effect / Work of compressor Vapour Compression Refrigeration System (VCRS)  System consists of (1) Evaporator (2) compressor (3) condenser and (4) expansion device.  In vapour compression refrigerator, vapour used as the refrigerant.  It is circulated in system in which it alternately evaporates (liquid to vapour) and condenses (vapour to liquid) thus it undergoes a change of phase.  In the evaporation it absorbs the latent heat from the space to be cooled.  In the condensing or cooling, it rejects Domestic Vapour Compression heat to atmosphere. Refrigerator Image source : kaizenlane.com Vapour Compression Refrigeration System (VCRS)  System consists of (1) Evaporator (2) compressor (3) condenser and (4) expansion device. Evaporator Expansion VCRS Compressor Device Condenser Vapour Compression Refrigeration System (VCRS)  Process (1-2) : Inlet of compressor (at point 1), low pressure and low temperature vapour enters the compressor. Compressor compresses the vapour at high temperature and pressure. The condition of refrigerant at exit to compressor (at point 2) is high pressure and high temperature vapour. Vapour Compression Refrigeration System Image source : chegg.com Vapour Compression Refrigeration System (VCRS)  Process (2-3) : High pressure, high temperature vapour coming from compressor condenses in the condenser by the rejecting heat to cooling medium. Cooling medium is usually air or water. The condition of refrigerant at exit to condenser (at point 3) is low temperature saturated liquid.  Process (3-4) : The saturated liquid coming from condenser passes through expansion device (throttling valve) where pressure of saturated liquid decreases from condenser pressure to evaporator pressure. The condition of refrigerant after throttling is low temperature and low-pressure liquid. Vapour Compression Refrigeration System (VCRS)  Process (4-1) : Liquid refrigerant coming from expansion device enters into evaporator where it absorbs latent heat of evaporation from space to be cooled (refrigerator compartment). Due to absorption of heat liquid refrigerant converted into saturated vapor or superheated vapour at low pressure and low temperature. Again, this vapour enters into compressor and the cycle is repeated. Vapour Absorption Refrigeration System (VARS)  System consists of (1) Evaporator (2) condenser (3) Generator (4) Absorber (5) Pump and (6) expansion device. Evaporator Expansion Condenser Device VARS Pump Generator Absorber Vapour Absorption Refrigeration System (VARS)  System consists of (1) Evaporator (2) condenser (3) Generator (4) Absorber (5) Pump and (6) expansion device.  In this system the refrigerant coming from evaporator is absorbed by absorber. The absorbing medium may be solid or liquid. In VAR system, the compressor is replaced by an Vapor Absorption Refrigeration System absorber and generator. Image source : mesubjects.net Vapour Absorption Refrigeration System (VARS)  Ammonia is refrigerant has characteristic as it is easily absorbed by water at low pressure and temperature, but at high pressure and temperature, the solubility of ammonia in water is reduced.  Therefore, when mixture of water and ammonia is heated by generator, the ammonia vapour is separated from water.  This principle is used in the vapour absorption refrigeration system.  Here the ammonia is refrigerant and water is absorbent. Vapour Absorption Refrigeration System (VARS) Working  Low pressure and low temperature vapour ammonia coming from evaporator enters in the absorber where ammonia is absorbed by weak solution coming from generator through throttle valve.  Due to absorption of NH3 in water, solution becomes strong. [In the mixture of NH3 and water, if amount of NH3 is less than water is called weak solution and if amount of NH3 is more than the water is called strong solution.]  During absorption process heat is released and rejected to cooling water.  The strong solution from absorber is pumped into generator, where it is heated and NH3 vapour separated from solution. In generator is supplied from external source. The weak solution is flowing back to absorber through throttle valve. Vapour Absorption Refrigeration System (VARS) Working  Again, weak solution in absorber absorbs NH3 vapour coming from evaporator. NH3 vapour coming from generator passes through condenser and condensed in condenser and reject heat to cooling medium.  Then liquid NH3 throttled through expansion device and it enters into evaporator.  In the evaporator NH3 evaporates by absorbing latent heat of evaporation to produce refrigerating effect.  Thus, the cycle is completed. Air Conditioning The basic function of air conditioning system is,  Cooling or heating of air.  Addition of moisture in air (Humidification) or removal of moisture from (dehumidification).  Purification, control movement or distribution of air and addition of fresh air from outside. Application of Air Conditioning  To provide cooling or heating and conditioning of air as per comfort of human being. This is known as comfort air conditioning.  To provide cooling or heating and conditioning air as per required in some engineering manufacturing and processing. This is known as industrial air conditioning.  The comfort air conditioning means conditioning of air in such a way that the human being can feel good.  Standard comfort conditions for human being are,  Temperature of air: Dry bulb temperature (DBT) 17° to 25° C  Moisture level: Relative humidity (RH) 30 to 70 %  Velocity of air 0.1 m/s to 0.25 m/s. Components of Air Conditioning  Fans: For circulation of air  Filters: For cleaning air  Heating element: Heating of air (It may be electric heater, steam, hot water)  Control system: It regulates automatically the amount of cooling or heating.  Grille: It adjusts the direction of conditioned air to the room.  Tray: It collects condensed water  Refrigerating plant: Provide cooling. It consists of compressor/generator and absorber, evaporator, condenser, expansion device (capillary tube). Components of Air Conditioning Fans Refri. Filters Plant Basic Components of AC Grill and Heating Tray Element Control System Classification of Air Conditioning According to arrangement of equipment's  Unitary System : Window Air Conditioner, Split Air Conditioner and Packaged Air Conditioner.  Central System. According to the purpose  Comfort air conditioning system  Industrial air conditioning system According to season of year  Winter air conditioning system: Air is heated and humidified  Summer air conditioning system: Air is cooled and dehumidified Window Air Conditioner  It mainly used for conditioning of air in the room.  The basic function of window air conditioner is to provide comfort cooling, dehumidification, filtering and circulation of air. Window Air Conditioner Image source : Google Window Air Conditioner 3D View of Window Air Conditioner Image source : Home Tips Split Air Conditioner  It is modification of window air conditioner.  This unit differs from window air conditioner.  In terms of split of unit into two parts. Split Air Conditioner Image source : Service AC 2017 Split Air Conditioner  In split air conditioner, the window air conditioner divided (split) into two parts.  First part: Includes the evaporator, filter, evaporator fan and grille (cooling coil). They placed inside the room.  Second part: Includes condenser, condenser fan, and compressor. This placed outside the room.  First part (inside of room) and second part (outside of room) is connected by small diameter tubes.  Therefore, small hole required in wall for installation of split air conditioner. References Books  Elements of Mechanical Engineering S.B.Mathur, S. Domkundwar; Dhanpat Rai & Sons Publications.  Basic Mechanical Engineering T. S. Rajan; Wiley Eastern Ltd.  Fundamental of Mechanical Engineering G. S. Sawhney; PHI Publication New Delhi.  Elements of Mechanical Engineering Sadhu Singh; S. Chand Publisher.  Elements of Mechanical Engineering P.S.Desai, S.B. Soni; Atul Prakashan References Weblinks  https://oelectrical.com/locomotive-boiler/  http://ecoursesonline.iasri.res.in/mod/resource/view.php?id=3822  https://www.khanacademy.org/science/physics/thermodynamics  https://byjus.com/physics/working-of-boiler/  http://www.vssut.ac.in/lecture_notes/lecture1429900545.pdf  https://nptel.ac.in/courses/112/105/112105129/ References Video links  https://www.youtube.com/watch?v=q7t1naS-kLs (Definition of Steam Boiler)  https://www.youtube.com/watch?v=nLJ5tT1E1k&list=PLuUdFsbOK_8qrZRQBP9 f3JHc0LBLjmFs2&index=6 (Boiler Working)  https://www.youtube.com/watch?v=IdPTuwKEfmA&list=PLuUdFsbOK_8qrZRQB P9f3JHc0LBLjmFs2&index=7 (Thermal Power Plant Working)  https://www.youtube.com/watch?v=PjsZGn4B6cw (Boiler Classification)  https://www.youtube.com/watch?v=sJEYSia8jTU (Cochran Boiler)  https://www.youtube.com/watch?v=dPllyDCYBKI (Babcock and Wilcox Boiler) References Video links  https://www.youtube.com/watch?v=xMAymzTl2gQ&list=PLpe3qgeJLpB2ObRN- ocQRdqAMuusbTGFf&index=6 (Lancashire Boiler)  https://www.youtube.com/watch?v=9mhYnQGZJuM (Locomotive Boiler)  https://www.youtube.com/watch?v=jqFmcrGKGmk (Steam Stop Valve)  https://www.youtube.com/watch?v=Os3aPpjQGsE&list=PLpe3qgeJLpB2LN- Wa36gUCKTuXnYicm7e&index=1 (Refrigeration and its importance)  https://www.youtube.com/watch?v=A5PJJdOL3ss&list=PLpe3qgeJLpB2LN- Wa36gUCKTuXnYicm7e&index=2 (Refrigerants)  https://www.youtube.com/watch?v=Q5PAXFxH2II&list=PLpe3qgeJLpB2LN- Wa36gUCKTuXnYicm7e&index=3 (Air Conditioning) References Video links  https://www.youtube.com/watch?v=L_6mBHOQxOc&list=PLpe3qgeJLpB2LN- Wa36gUCKTuXnYicm7e&index=4 (Air Refrigeration System)  https://www.youtube.com/watch?v=h5wQoA15OnQ (Refrigerator Working)  https://www.youtube.com/watch?v=7NwxMyqUyJw (How does a refrigerator work?)  https://www.youtube.com/watch?v=gVLhrLTF878&list=PLuUdFsbOK_8qrZRQB P9f3JHc0LBLjmFs2&index=1 (Air Conditioning Working) References Research Paper Links / Journal Links  https://www.power-eng.com/2013/06/12/advances-in-boiler-cleaning technology/#gref (Advances in Boiler Cleaning Technology)  https://www.rfmacdonald.com/boiler-case-studies/ (Boiler Case Studies)  https://www.energy.gov/eere/articles/5-new-air-conditioning-technologies- keep-you-cool (Energy Efficiency)  https://www.tandfonline.com/doi/full/10.1080/23744731.2017.1334502 (Recent advances on heat and mass transfer in RAC systems)  https://www.journals.elsevier.com/international-journal-of-refrigeration/most- downloaded-articles (Journal of Refrigeration).  https://www.worldscientific.com/worldscinet/ijacr (International Journal of Air-Conditioning and Refrigeration www.paruluniversity.ac.in