Thermodynamics Lab Manual

Name of the student: _______________________________________________ Semester/Section: ________________________RollNo:____________________Date: _______________________________________________________

EXPERIMENT NO.1STUDY OF DIFFERENT BOILERS

AIMTo Study about the different boilers.

LEARNING OBJECTIVES

What is a boiler ?Uses of a boiler ?The requirements of a good boiler.The classifications of a boiler.Principle parts of a boiler and their functions.Boiler mountings and their accessories.Features of a good boiler.Applications of different boilers.

DEFINITION

RCET/Department of Mechanical Engineering/ Thermodynamics Laboratory

1


Steam is one of the most important engineering works. According to A.S.M.E. code a steam generating unit i.e. boiler is defined as follows:A combination of apparatus for producing furnishing or recovering heat together with the apparatus for transferring the heat so made available to water, which could be heated and vaporized to steam form.

REQUIREMENT OF A GOOD BOILERA good boiler should be able to fulfill the under noted conditions:

It should be capable of generating the maximum quality of steam at required pressure and temperature and quality with minimum fuel combustion. It should be light in weight and

should not occupy much space.


2


It should be safe in working and should conform to the safety regulations laid down in the boiler act. It should be capable of quick

starting. The initial cost, installation cost

and maintenance cost of the boiler should be low.

All parts and components should be easily accessible for inspection and repair but in such a manner that it should have minimum number of joints.

CLASSIFICATION OF BOILERBoiler is classified on the basis of following:1) Tube contentsFire tube boilerIn the fire tube boiler the hot gases pass through the tubes and water surround them. Example: Cochran boiler, Lancashire boiler, Cornish boiler, Locomotive boiler.


3


(b) Water tube boilerWater flows through the tubes and fires surrounds the tubes. Example: Babcock & Wilcox boiler, Stirling boiler.Method of firing(a) Internally fired boilerAs their name implies the furnace region is provided inside the boiler shell. Example: Lancashire boiler, Locomotive boiler & Scotch boiler.(b) Externally fired boilerThe furnace region is provided outside the boiler shell. Example: Babcock & Wilcox boiler.Pressure of steamLow pressure boilerPressure is less then 80 bar. Example: Lancashire boiler, Locomotive boiler, Cochran boiler, Cornish boiler.High pressure


4


Example: Pressure greater than 80bar are Cochran, Cornish, Lancashire boilers and locomotive boilers are low pressure type whereas Babcock Wilcox, Lamont and Benson are high pr. Boilers.Method of circulationNatural circulationIn this type circulation of water takes place by natural convection current produced by the application of heat.e.g.: Lancashire, Locomotive & Babcock Wilcox Boilers.Forced circulationIn this type of boiler circulation of water takes place by mechanical means like pumps. Example: Lamont boiler, Velox boiler, Power boilerNature of servicesStationary at a place.Portable, so can be moved easily and dismantled and transported from one place to another


5


Mobile so can be fitted on vehicle.Position and number of drumsHorizontal (b) vertical (c) inclined.Gas passageSingle pass (b) multi pass.Nature of draughtNatural draught boilerAs the name implies the draught is produced by natural airForce draught boilerThe draught is produced by mechanical means such as fans.Heat sourceCombustion of solid, liquid and gaseous fuelElectrical or nuclear energy andHot waste gases, which are by- products of other chemicals processes.Once through boilerIn this type there is no circulation of water so that the water leaves the tubes as steam. e.g. Benson boiler.Fluid used


6


Steam boilerIn this water is working fluidMercury boilerIn this mercury is working fluid.Boiler shell materialCast iron boilerUsed for low pressureMercury boilerSuitable for high pressureCopper and stainless steelThis is suitable for miniature type of boiler.

QUESTION BANK

Define a Boiler.What is the use of Boilers?What is the important working substance used for power generation in steam Engines & steam turbines?What are the classifications of boilers?What are the principle parts of boilers?


7


What are the functions of the principle parts?What are boiler mountings?What are boiler accessories?What are the uses of steam in industries?What are the features of a good boiler?What is the difference between water tube and fire tube boiler?Differentiate between externally fired and internally fired boilers?Classify boilers on the basis of pressure of steam?What is the basic difference between portable, Stationary & mobile boilers?What do you mean by natural and forced circulation boilers?What is draught?What do mean by natural and forced draught boilers?Give an example of steam generator used in daily life?*****


8


EXPERIMENT NO. 2BABCOX WILCOX WATER TUBE BOILER

AIMTo study about the Babcock Wilcox water tube boiler.

LEARNING OBJECTIVESDifferent partsMountings used.Accessories used.Applications – Sugar Industries.

INTRODUCTIONThe water tube boilers are used exclusively, when pressure above 10 bars and capacity in excess of 7000kg of steam per hour is required. Babcock & Wilcox water tube boiler is an example of water tube boiler and may be designed for stationary or marine purpose.


9


Babcock and Wilcox boiler belongs to the following categories: (I) Stationary Type, (II) Horizontal drum type, (III) water tube type, (IV) Externally fired, (V) Low Pressure, (VI) Natural circulation, (VII) Coal fired.

The specifications relating to this boiler are given below:Diameter of the drum 1.22 to 1.83 mLength 6.096 to 9.144 mSize of water tubes 7.62 to 10.16 cmSize of superheated tubes 3.84 to 5.71 cmWorking pressure 11.5 to 17.5 bar(max. 40 bar)Steaming capacity 40,000 kg/hr (max.)Efficiency 60 to 80 %.

CONSTRUCTION


10


Babcock Wilcox water tube boiler consists of a high-pressure drum mounted at the top. Generally the drum of the boiler is made of welded steel or single course joined. The heads of the drums are forced by hydraulic pressure and are dished to a radius equal to the diameter of the drum. From each end of the drum, connections are made with the upper header and down take header. The water tubes are inclined 5-15 degrees to promote water circulation. The water tubes are solid drawn steel tubes about 10 cm. in diameter and are expanded into the bore holes of the headers to ensure proper fixing. The headers have a serpentine (sinusoidal) form. This serpentine form of headers arranges the water tube such that they are staggered and this exposes the complete heating surface to flue gases. The heating


11


surface of the unit is outer surface the tubes and half of the cylindrical surface of the water drum, which is exposed to flue gases.


12


A mud box is attached to the bottom of the rear header (that is down take header). Any foreign material held in suspend is on the water gets collected in the mud box due to gravity and it can be blown off from time to time to clean the outside of the water tubes and to remove the soot a door is provided so that access to the interior of the boiler can be made.The whole of the assembly of water tube is hung along with the drum from a steel girder frame by steel rods called slings in room made of masonry work lined with fire bricks. The sling passed around each of the drum and is thus entirely independent of the brickwork of the setting. The boiler can expand or contract without starting the brickwork setting.


13


Below the uptake header the furnace of the boiler is arranged. The coal is fed to the chain grate stoker through the fire door. The changing speed is so adjusted that by the time the coal reaches the other end the grate its combustion has been completed. There is bridge wall deflector, which deflect the combustion gases upwards. Baffles are arranged to provide three passes of the flue gases across the water tubes to act as deflectors for the flue gases and to provide for the gas passes. A chimney is provided for the exit of the gases. A damper is placed at the inlet of the chimney to regulate the draught. There are super heating tubes for producing super heated steam.

NAMES OF DIFFERENT ACCESSORIES ARE AS FOLLOWS:


14


Drum 11) Super heaterPressure Gauge 12) BafflesWater Gauge 13) Water tubesSafety Valve 14) Fire grateFeed water inlet 15) Ash PotManhole 16) Clean out doorsHeaders 17) RiserDown come 18) Blow off pipeNon return valve 19) ChimneyAnti priming pipe 20) DamperSuper heater 21) Fire Door

WORKING PRINCIPLE


15


The hot combustion gases caused by burning of fuel on the grate rise and are deflected upwards by the bridge wall deflector and pass over to the front portion of the water tubes and drums. By this way they complete first pass. With the provision of baffles they deflect downward and complete the second pass. Again with the provision of the baffles they rise upwards and complete the third pass and finally come out through the chimney. During their travel they7 give heat to the water and steam is formed.


16


The circulation of water in boiler is natural circulation set up by the convective currents. A feed water inlet pipe supplies feed water. The hottest water and steam rise from the tubes to the uptake header and then through the riser enters the boiler drum. The steam vapor escapes through the water to the upper half of the drum. The cold water flows from the drum to the rear header and thus the cycle is completed.


17


To get superheated steam: the steam accumulated in the steam space is allowed to enter the superheated tubes which are placed above the water tubes, the flue gases passing over the flue tubes produces superheated steam. The steam is thus superheated and is finally supplied to the user through a steam and stop valve. It is to be noted that when the steam has to be raised from the drum water level, the super heater remains flooded until the steam reaches the working pressure. The super heater is then drained and the steam is allowed to enter in it for superheating purposes.

QUESTION BANK

Is this a water tube / fire tube type of boiler? Why?


18


Why are water tubes inclined and at what angle?Where does combustion of fuel takes place? How?What is the function of the mud-box?What is the working principle of this boiler? Explain with the help of a neat sketch.What are the merits and demerits of Water tube boilers over fire tube boilers?Where is Babcock & Wilcox boilers generally used or give the application of Babcock & Wilcox boiler?What is the range of evaporative capacity of Babcock & Wilcox boiler?How much is the operating pressure range of Babcock & Wilcox boiler?To what angle is the water tubes generally inclined to in Babcock & Wilcox boiler?


19


What is the shape of the headers? Why is this shape provided?Why are the baffles provided in Babcock & Wilcox boiler?What is a fire bridge wall deflector?Explain the path of the flue gases in Babcock & Wilcox boiler?*******


20


EXPERIMENT NO. 3STUDY ABOUT LANCASHIRE BOILER

AIMTo study about Lancashire boiler.

LEARNING OBJECTIVETo know the different parts of the boilerThe Mountings & Accessories of the boiler.Working PrincipleApplication

INTRODUCTIONA Lancashire boiler is a stationary or land type boiler with fire, horizontal, straight tube, internally fired having natural circulation. The boiler is popular because of simplicity of design and ease of operation. It is commonly lead in sugar mills & Textile industries.


21


The specifications of Lancashire boiler are given below:Diameter of the shell 2 to 3 cmLength of the shell 7 to 9 cmMaximum working pressure 16 barSteam capacity 9000 kg/hrEfficiency 50 to 70 %.

CONSTRUCTIONAL DETAILSThe figure shows a schematic diagram of a Lancashire boiler along with brickwork setting. Some of the important parts are numbered for the ease of description. The parts are as flows:Feed check valveFeed water is supplied the boiler under pressure, the valve checks it’s escaping back.Pressure gaugeIs for measuring the pressure of the steam.Water level gaugesIndicates the level of water.Dead weight valve


22


Is for safety against pressure in excess off rated pressure.Steam stop valveOpens and closes the supply of steam for use.ManholeIs for cleaning and inspecting the drum.Low water high stem safety valve


23


Is for blowing out steam if he steam pressure is higher than the working pressure and blowing out steam when the water level in the boiler is low.Fire grateThe grate in which fuel is burnt.Fire bridgeThis is used for deflecting the gases of combustion upwards.

Fire tubesAre for the first pass of flow of flue gases. To accommodate a grate of sufficient area and minimum length the flue tubes are tapered being larger in diameter at the front and smaller at the back.Boiler shell


24


Is for containing water and steam. it also contains tubes inside if the boiler is internally fired. The boiler shell is made from several welded or riveted rings of seimen’s martin open-hearth steel plates.Bottom flueSide flueDampersAre for controlling the flow of flue gases. Generally these are iron doors, which slide up and down in iron groves (in the side flue) by means of chain ropes or pulleys.Main flueDoorsAre provided in the front brick and in the top brickwork for cleaning the flues.Ash pitIs for depositing ash.Blow off cock


25


Is provided at the bottom of the shell by a bent pipe to blow off sludge at intervals since the water shell is not perfectly horizontal.A few degrees fitting towards the front enables all the sediments in front near the blow off cock.Blow of pits for disposing off the blow off water.Gusset straysIs for securing and stiffening the four corners of the shell.Perforated feed pipesIs used for feeding water uniformly.Antipriming deviceIs used for separating out suspended moisture and allowing as far as possible the dry steam through the stop valve.Fusible plugIs for safety against the flue tube too excessive heat when water level falls too low.


26


WORKING PRINCIPLEThe fuel is burnt on the grate and as a result hot combustion gases are produced. The flue gases move along the furnace tube or the main flue and deflected up by fire on the main flue, they deflect downwards and travel through the bottom flue as shown. The bottom flue is situated below the water shell and heats the lower position of the shell. After traveling from back to front this flue gases bifurcate into separate paths the side flue. Now they travel from front to back in the side flue and thus heat the side of the water shell. After these two streams or flue gases meet again, the main flue passing through damper from which they are discharged to atmosphere through the chimney.

QUESTION BANK


27


Is Lancashire boiler a fire tube or water tube type?On what basis are fire tube boilers classified?What are the classifications of a fire tube boiler?What are the specifications of a Lancashire boiler?Where is it used?What is its working pressure of this boiler?What is its steam generating capacity?What are flue gases?Explain the working principle of a Lancashire boiler with a neat sketch?What are the functions of the principle parts of this boiler?What is a smoke tube or fire tube?What do you mean by grate?What is Fire Bridge?What is the use of damper?What is the function of chimney?


28


Which type of steam is generated inside a boiler?What do you mean by main flue, bottom flue & side flue in a Lancashire boiler?What is the use of an anti priming device?Which type of fuel is used in Lancashire boiler?What is a man hole and what is its shape?Why is man hole elliptical in shape?********


29


EXPERIMENT NO. 4STUDY THE COCHRAN BOILER

AIMTo study the Cochran boiler.

LEARNING OBJECTIVETo know the different parts of the boilerThe Mountings & Accessories of the boiler.Working PrincipleApplication

INTRODUCTIONThe Cochran boiler is one of the most popular and best types of boilers.


30


Cochran boiler belongs to the following categories: (I) Stationary Type, (II) Vertical type, (III) Fire tube type, (IV) internally fired, (V) Low Pressure, (VI) Natural circulation, (VII) Coal fired.

SPECIFICATIONSThe specifications of Lancashire boiler are given below:Diameter of the shell 2.75 mHeight of the shell 5.79 mMaximum working pressure

6.5bar(max. pressure=15bar)Steam capacity 3500 kg/hrHeating surface 120 m2

Efficiency 70 to 75 %.(Depending on the fuel used)

CONTRUCTIONAL DETAILS


31


It consist of a vertical shell having a hemispherical shape and a furnace which also have the same shape i.e. hemispherical, both are made by a singleHydraulically pressed plate without a single steam or joint to have the strongest structure under compression. The fire grate and ash pot is arranged in such a manner as shown in figure. In the firebox fire door and damper are also provided adjacent to the firebox. The box has a combustion chamber, which is dry backed and lined with firebricks. Close to the combustion chamber a number of horizontal smoke tubes are provided. These tubes are of equal length and arranged in a group with wide space in between them and shell so as to help convection currents. At the end of these smoke tubs are fitted in the smoke box tube plate and combustion


32


Chamber tube plates. Generally the tubes are made of mild steel plate and smoke bore made of steel plate. Smoke box is fitted with hinged door that gives an easy access to smoke tubes for cleaning and inspection’s stock is provided at the top of the smoke box for discharge of the gases. The smoke tubes and the furnace are also surrounded by water on all sides except at the opening for fire door and combustion chamber.

WORKING PRINCIPLE


33


The hot gases produced from the burning of fuel on the grate rises up through he flue pipe and reaches the combustion chamber’s flue gases from the combustion chamber pass through the fire tubes and smoke box finally are discharged through the chimney. The fuel gases during their travel from the fire box to the chimney gives heat to the surrounding water to generate steam.Arrows shows the circulation of water in the shell the watercourses down by the cooler wall of the shell and rises up past the fire tubes by natural circulation due to convective current.

QUESTION BANK

Is Cochran boiler a water tube or Fire tube type?What are its specifications?What are the classifications?


34


Explain the working its working principle with a neat sketch?What are its principle parts?What are the functions of the parts?What are the various mountings used?What are the accessories used? Are accessories used?What are the applications of Cochran boiler?What is the material used in construction of the shell of Cochran boiler?What is shape of fire box in Cochran boiler?What is the mode of heat transfer taking place in a boiler?What is the mode of circulation of water in a Cochran boiler?What is an ash pit?What is the use of a man hole?

***********


35


EXPERIMENT NO. 5STUDY OF LOCOMOTIVE BOILER

AIMTo study the locomotive boiler.

LEARNING OBJECTIVESDifferent partsMountings used.Accessories used – No accessories are used.Applications -- Wherever less space is required(E.g.)- In Power-Plant, since portable. .

DEFINITION


36


The locomotive boiler is a horizontal, multitubular, natural circulation, artificial Draught, internally fired, portable fire tube boiler it is capable of meeting the sudden and fluctuating demands of steam which may be imposed on it because of variation of power and speed of a locomotive engine it is generally used in places where semi portability is necessary.

Max. Press. Range is 21 bars.Steam rate is as high as 55 to 70 kg. /sq. meter of heating surface/hour.

CONSTRUCTION


37


It consist of cylindrical steel shell or barrel there is rectangular fire box at the back end of shell which formed a combined grate and combustion chambers the fire box is water cooled on the three sides except the bottom the best heating surface of boiler is that which surrounds fire box.

VARIOUS PARTS AND THEIR USES1) FIRE BOX : In which the combustion takes place.2) GRATE : On which fuel burns.3) FIRE HOLE : To introduce solid fuel.4) FIRE BRIDGE ARCH : To give wanted dir. to the hot flue gases.5) ASH PIT : To control ash of coal.6) DAMPER : To control the quantity of air entering firebox.7) FIRE TUBE : For transmission of hot flue gases.


38


8) BARREL OR SHELL : To hold steam & all accessories.9) SMOKE BOX : For collection of flue gases after heating water.10) CHIMNEY : For delivery of hot flue gases to atmosphere.11) EXHAUT STEAM PIPE : To create artificial draught.12) STEAM DOME : To collect steam at high pressure.


39


13) REGULATOR: To direct steam to super heater header.14) LEVER: Mechanism for super heating steam.15) SUPER HEATER TUBES: Short diameter Tubes, which are insertedin fire tubes.16) SUPER HATER HEADER: To give extra heat to steam.17) SMOKE BOX DOOR: Large door, used for examining &cleaningpurpose of boiler.18) FEED CHECK VALVE: For safety purpose of boiler.19) SAFETY VALVE: For extra safety purpose of boiler.20) WHISTLE: Giving whistles.21) WATER GAUGE: To check water level.

WORKING PRINCIPLE


40


The coal introduced in firebox through fire hole is burnt on grate. The hot flue gases rising from grate are deflected upwards by fire brick arch so that they come into intimate contact with walls & roofs of firebox.There are number of horizontal smoke tubes through which hot gases pass from furnace to smoke box. They are fixed being suspended both the end plates of the barrel & immersed in water.The hot gases from smoke box are discharged to atmosphere through short chimney for traveling easiness of locomotive.During the travel of hot flue gases from grate to chimney they give heat to water & generate steam which is collected in steam dome.


41


The driver in the cabin operates regulator by turning the lever, which leads dry sat. Steam to the engine for expanding & doing work. To get super heated steam, steam is directed to super heater header with the help of regulator & lever arrangement. The hot gases passing through the fire tube supply heat to the super heater tubes that has steam inside the super heater tubes which is super heated .The super heated steam thus formed is supplied to the engine by an outlet pipe attached to super heater header.

QUESTION BANKWhat are the classifications of locomotive boilers?What are its specifications?Explain the working its working principle?What are its principle parts?


42


What are the functions of the parts?What are the mountings used?What are the accessories used?What are the applications of locomotive boilers?******


43


EXPERIMENT NO –6BOILER MOUNTINGS & ACCESSORIES

AIMTo study the different boiler mountings & accessories.

LEARNING OBJECTIVESDifferent fittings and devices.Different mountings used in boilers.Different accessories used.Functions of the various mountings and accessories used.Difference between mountings and accessories.

INTRODUCTIONMOUNTINGS


44


Mountings are different fittings and devices are necessary for the operation and safety of a boiler. Usually these devices are mounted over boiler shell.In accordance with the Indian boiler regulation the following mounting should be fitted to the boilers.Two safety valves.Two water level indicators.A pressure gauge.A feed check valve.A blow off cock.A steam stop valve.A man holeMud holeA fusible plug

WATER LEVEL INDICATOR


45


In indicate level of water inside the boiler. This fitting may be seen in the front of the boiler. And are generally two in number. The water level indicator consists of two cocks. C1 and C2 put the glass tube in connection with the steam space. Water cock C2 puts the glass tube in connection with the water in the boiler.In the working of a steam boiler and for proper functioning of water level indicator, the steam water cocks are opened. In this case, the handles are placed in a vertical position in the figure. The rectangular passage at the end of the glass tube contains two balls.In case the glass tube is broken, the two balls are carried along its passages to the ends of the glass tube, so the steam and water will not escape out. The glass tube can be easily replaced by closing the steam and water cocks.


46


PRESSURE GAUGEPressure gauge in used to measure the pressure of the steam inside the steam boiler. It is fixed in front of the boiler. Pressure gauge used on a boiler in generally of the Bourden type.The detail of pressure gauge in which the Bourden tube in connected by levers and gears to the pointer. The fluid pressure, when transferred to Bourden tube, tries to make its cross section, originally elliptical, unit circular cross section. In this process the tube moves out as indicated by the arrow. This motion results in the pointer moving over a circular scale indicating the pressure.

SAFETY VALVE


47


The dead weight in calculated based on the working pressure (p) and the area of cross section of valve (a) acted upon by the pressure, such that

(w + W) = p.a.

When the pressure of steam exceeds the normal pressure, the valve as well as the carrier is lifted up from its seat. This enables the steam to escape.DEAD WEIGHT SAFETY VALVEThe figure shows diagrammatically the arrangement of a dead weight safety valve the dead weight is calculated based on the working pressure, p and area of cross section of valve (a) acted upon by pressure such thatW+w =p*a


48


When the pressure of steam exceeds the normal pressure the valves as well as the carrier are lifted up from its seat enabling the steam to escape

LEVER SAFETY VALVELever safety valve consists of a lever and weight W. one end of the lever is hinged with the other end is suspended a weight W.When the steam pressure becomes greater than the normal working pressure, the valve is lifted with the lever at the weight. Consequently the steam escapes through the passage between the valve seat and the steam pressure decreases.

P = Steam pressured = diameterW= weight suspended on the leverW1 = Weight of lever acting at the C.G


49


Wv = Weight of the valveA= / 4d2, cross section area of the valve

Taking moment apart the fulcrum F,W x AF + W1xGF + Wv x VF = p x a x VF

From the above equation, we can find the weight W or length of lever for a given pressure of steam (p)

SPRING LOADED SAFETY VALVEFor, locomotive and marine engines both the lever and dead weight types are unsuitable. The spring loaded safety valve is suitable, since it in unaffected by vibration or deviation from vertical.


50


Rams bottom spring-loaded safety valve. It consists of two separate valves and settings have one lever and loaded by a spring, the spring being placed between the valves. The tension of the spring cam be adjusted according to the steam pressure. By pulling or raising the lever the can relieve the pressure from either valve separately.

BLOW OFF COCK:A blow off cock performs the two functions: -It may discharge a portion of water when the boiler is in operation to blow out muds, scale or sediments periodically.It empties the boiler when necessary for cleaning and repair.It is fitted at the lowest part of the water space on the boiler.


51


A commonly used type of the blow off cock is shown in fig. It consists of a conical plug fitted accurately into a similar casing .The plug has a rectangular opening which may be brought with the line of passage of the casing by rotating the plug. This causes the water to be discharged from the boiler. Rotating the plug again may stop the discharging of water.

BOILER ACCESSORIESBoiler accessories are required for steam boilers for their proper operation and for the increase of their efficiency. Commonly used boiler accessories are:1. ECONOMIZERAn economizer is a device in which the waste heat of the flue gases is utilized for heating the feed water. As the name indicates, the economizer improves the economy of the steam boiler.


52


e.g. Suppose in a boiler the steam formed has enthalpy h KJ/kg at pr. p and water is supplied at 25oC say the enthalpy of water is (hfl)So, total heat supplied for generating the steam at pressure p = (h-hfl) KJ/kg. If economizer is installed in the path of flue gases and feed water is supplied through economizer and say the water in heated upto 50oC and again the steam is generated at pressure p with enthalpy h KJ/kg.Now, total heat supplied for generating steam at pressure .p= (h-hf2) KJ/kg.Say hf2 in enthalpy at water at temperature 50oC since hf2>hf1 .So, (h-hf2) < (h-hf1). So, by installing the economizer heat supplied to generator the steam is reduced.The use of an economizer has the following advantages:-


53


The temperature range between various parts of boiler is reduced which results in reduction of stress due the unequal expansion.Evaporation capacity of boiler is increased.Overall efficiency of plant is increased.

AIR PREHEATER:The function of air pre heater is to increase the temp. of air before it enters the furnace . It is generally placed after the economizer so the flue gases pass through the economizer and then to the air pre heater.The preheated air accelerates the combustion and facilitates the burning of coal.


54


Figure shows the tubular type of air pre heater . The flue gas after leaving the boiler or economizer travel through the inside of the tubes of air pre heater in a direction opposite to that of air travel and transfer some of their heat to the air to be supplied to the furnace. Thus the air gets initially heated before being supplied to the furnace. The gases reverse their direction near the bottom of the air heater, and a soot hopper is fitted to the bottom of air heater casing to collect soot.

Super heater:The function of a super heater is to increase the temperature of the steam above its saturation temperature.Super heaters are located in the path of the furnace gases so that heat is recovered by the super heater from the hot gases.


55


There are two types of super heatersConvective super heaterRadiant super heaterConvective super heater is placed in the path of the flue gases.A radiant super heater is placed in the furnace and the wall tubes receive heat from the burning fuel through radiant process.

QUESTION BANKWhat are mountings?Why are mountings necessary?Name the mountings of a boiler?What are the functions of the various mountings of a boiler?What is the material of dead weight safety valve?What are the advantages and disadvantages of a dead weight safety valve?In which boiler is spring loaded safety valve used?


56


In which boiler is High steam low water safety valve used?What are the parts of a High steam low water safety valve?What are the parts of a lever safety valve?What are the parts of the parts in a water level indicator?Why is a fusible plug used?What is the material of fusible plug?Why are pressure gauges used?What is the principle function of a steam stop valve?What is the material of steam stop valve?What is the function of feed check valve?What is the function of Blow-off-cock?Why are accessories used?Can a boiler work safely without an accessory?Where are accessories mounted in a boiler?


57


Name the different accessories?What is the purpose of installing superheater?Where is super heater mounted?What is the purpose of Economizer?Name an Economizer?What are the specifications of an Economizer?What are the different parts of an Economizer?What is its material?What are its different parts?What are the advantages of using it?Why is an Air-Heater used?What is the use of Steam Injector?What is the use of feed pump?What is the use of Steam Trap?***************************************************************************************************************************************


58


EXPERIMENT NO: 7STEAM ENGINE

AIMTo study the different types of steam engine.

LEARNING OBJECTIVESClassification of steam engines.Requirements of a good boiler.Selection of boilers.Boiler Terms.

INTRODUCTION

The steam Engine is a reciprocating type of basic prime mover, which utilizes steam as the working medium to convert the heat energy into mechanical work.


59


The first steam engine was developed by James Watt in 1763 but steam engine has very low efficiency so a now days they are loosing their values and replaced by efficient engine like diesel and electric engine.

CLASSIFICATION OF STEAM ENGINE

Steam engine may be classified as described below:

Axis of CylinderOn the basis of position of the axis of the cylinder the steam engine are classified asVerticalHorizontalInclinedAction of steamAccording to this fact there are two types.Single acting.Double acting.


60


In single acting steam engine steam acts on one side of piston only while in the double acting steam engine steam is alternatively admitted on both sides of the cylinder.

Number of cylinder:-On the basis of on of cylinder may be classified asSimple.Compound.In a simple steam engine total expansion of steam takes place in one cylinder while in the compound engine the total expansion of steam takes in more than one cylinder.

Exhaust systemOn the bases of exhaust system there are again two-typeCondensing.Non- condensing.


61


In a condensing engine the exhaust is condensing in a closed vessel where the backpressure steam is reduced (condenser) and in non-condensing the exhaust is led to the atmosphere as in locomotive.Valve gearsOn the busies of valve gear it may by classified asD type and.Corlis or poppet type.Speed –on basis of speed there are three types.Low.Medium and.High.UseOn the basis of use it may by classified as.Stationary.Locomotive.Marine etc.


62


PRINCIPAL PARTS OF A SIMPLE STEAM ENGINE

As shown in figure the principal parts of a steam engine are: -

FrameIt is generally made of cast iron and support the moving and stationary parts if the engine.

CylinderThis is a chamber in which the piston moves to and fro due to the action of steam one end of cylinder is closed by mean of separate cover called end cover, the other is known as crank end through which the piston rod passes it is made of cast iron and bolted with the frame.

Steam chest


63


This is generally cast integral with the cylinder. It is closed by a cover termed as steam chest cover, which may be circular, or rectangular depending upon the shape of the valve operating in it. There are two ports called inlet port and exhaust port made in the casting for connecting the steam chest to the cylinder. The inlet port serves as a passage for the admission of steam from the steam chest to the cylinder where as the exhaust port serve as a passage for the exhaust steam from the cylinder to exhaust pipe.

Piston


64


The piston is a cylindrical piece generally made of cast iron. Due to the action of steam by moving to and fro in the cylinder it transmit forces to the crosshead through the piston rod. Since the movement of piston allows the expansion of steam in the cylinder and so the work is obtained.

Piston ringThe function of piston rings is to prevent the leakage of steam past the piston and to prevent the any were and tear taking place in the piston. Whatever the wears and tear take place on the piston rings, which can be easily, replace. These are generally made of cast iron and are located in the circumferential grooves cut in the piston.

Piston Rod


65


The piston rod connects the piston and crosshead it is generally made of mild steel.

Stuffing BoxThis is placed at the point where the piston rod passes through the cylinder cover. In this way it prevents the leakage of steam from the cylinder to the steam atmosphere.

Cross HeadIt connects the piston rod and connecting rod and moves both the guides. The function of cross head is to prevent the piston rod from getting bent.

Connecting Rod


66


One end of the connecting rod is connecting rod to the cross head by gudgeon pin and the other end is connect end to the crank. The function of connecting rod is to make convert the reciprocating motion of the piston into rotary motion of the crank made of forged steel.

Crank shaftThe crankshaft is one of the most important parts of the engine and sever the propose of converting the force applied by the connecting rod into a rotational force. It is free to rotatein main bearing. Alloy steel carbon steel or cast iron steel is usually employed in forging the crankshaft.Valve


67


It reciprocates over the valve seat in the steam chest by the eccentric so located on crankshaft relative to crank so as to admit or exhaust steam to and from cylinder at the proper time through the parts. It may be slide or any other type.

EccentricIt actuates the valve rod at the appropriate time. It is made of cast iron and is located on the crankshaft.

Valve rod & Eccentric Rod


68


The valve rod connects the valve and the eccentric rod through a valve rod guide, which prevent the bending of the rod and the eccentric rod connects the valve rod and the eccentric. The eccentric rod the converts the rotary motion of eccentric into reciprocating motion, which is transmitted to valve rod. Both the rods are made of mild steel or alloy carbon steel.

Fly WheelThis is a heavy mass which absorbs energy when the supply is greater than the demand and release it when the supply is less than the demand. Thus minimizes the rapid fluctuation of speed in a revolution.

Governor


69


The function of a governor is to maintain the speed of engine fairly constant irrespective of the load. It is placed generally at the inlet of the steam pipe and is driven by a belt through the crankshaft.

Main BearingGenerally two main bearing are attached provided at each of the crankshaft to support it the bearings are attached the frame.

WORKING PRINCIPLE


70


In order to understand the working of a steam engine, consider a simple double acting, non-condensing D-slide valve type engine. Now let the superheated steam at a high pressure about 20 atm from the boiler is fed into the steam chest after this the steam makes it way into the cylinder through the any of the ports ‘a’ or ‘b’ depending on the position of ‘D’ slide valve.


71


When port ‘a’ is opened the steam rushes into left side of the piston and forces it to right. At this stage the slide valve covers the exhaust port and the port ’b’ as shown. Since the pressure of the steam is greater on the left side than that on the right side the piston moves to the right. When the piston moves to the extreme right it crosses the port ‘a’ and exhaust port. The steam port ‘b’ now open and steam rushes to the right side of the piston. This movement of the steam forces the piston to the left and at the same time of exhaust steam goes out through the exhaust pipe, and thus completes the cycle of operation. The same process is repeated in another cycle of operation and as such the engine works.

QUESTION BANKWhat is prime mover?


72


What is reciprocating Steam engine?What is the classification of reciprocating Engine?What are the important parts of a steam engine?What are the functions of the various important parts?What are the Steam Engine Terminologies used and define?What are the uses and applications of a steam engine?


73


EXPERIMENT NO.8STUDY OF COMPOUND STEAM ENGINE

AIMTo study about the method of reducing cylinder condensation i.e. “Compound steam engine”.

LEARNING OBJECTIVESDefinition of Compound Steam Engine.DescriptionWorking PrincipleMethods of Compound Steam Engine.

DEFNITION, DESCRIPTION & WORKING


74


Theoretically as we know that by definition by expanding the steam in a series of cylinder instead of one, the temperature range per cylinder is reduced which reduces the condensation. So using this concept such type of engine “ engine which are built with two or more cylinder for the successive expansion of steam are known as Compound steam engine”. The cylinder in which expansion takes place is known as high pressure (HP) cylinder. The exhaust from the high-pressure cylinder is passed on to do work in the second cylinder, which is known as low pressure (LP) in the case of double expansion engine. After this the steam exhaust to the condenser. A three cylinder compound steam engine is called a triple expansion engine in which the middle cylinder is called the intermediate pressure (IP) cylinder. It is


75


uncommon to find triple expansion engine. A four cylinder compound steam engine is called a quadruple expansion engine. These types of engines are generally not used.Compound steam engines are found in capacity from 50 to 4000k. They are used for marine services and for driving machines in mills.

METHODS OF COMPOUNDING STEAM ENGINEDepending upon the arrangement of the cylinder and crank, compound steam engine are divided into two categories as follows:1. Tandem compounding2. Cross compoundingWolfe type compoundingReceiver type compounding.

1. Tandem compounding


76


In tandem compound steam engines, the piston of H.P. cylinder has common piston rod, crosshead, connecting rod and crank. In addition to this both the cylinders are in the same straights line. Since there is common piston rod and crank, the operation in the both the cylinders are in phase and the Max. and Min. turning moment occur approximately in turning moment and consequently. It needs a large flywheel, thus balancing and vibration problems are not minimized in this arrangement.

2) Cross compoundingWolfe type


77


As shown in figure the in Wolfe type compound steam engine the crank of two cylinders are 180° out of phase. This means that the time of exhaust of the H.P. cylinders coincides with the time of admission of the L.P cylinder would pass directly to the L.P. cylinder and hence both the cylinders are arranged side by side.

Receiver type


78


In the receiver type compound steam engines, the cranks of the cylinders are placed 90° out to each other. The stroke of the two cylinders is thus out of phase and high pressure steam from H.P. cylinder cannot be exhaust the L.P cylinder. Instead the H.P cylinder exhaust into a vessel called a receiver. This receiver is placed both the H.P and L.P. cylinder and holds the steam until the L.P cylinder is ready to receive it. In order to minimize the fluctuation in the pressure the receivers must be large enough at least 1.5 times the H.P. cylinder valve. For the receiver type the turning moment variation is more which the main advantages of the receiver type arrangement are. Since the variation in turning moment is small it needs a smaller flywheel.

QUESTION BANK


79


How many cylinders does a compound steam engine have?Describe the working of a compound steam engine with a neat sketch.


80


EXPERIMENT NO: 9TWO STROKE PETROL AND DIESEL ENGINE

AIMTo study the working principle of two stroke Petrol and Diesel Engines.

LEARNING OBJECTIVESWhat is TDC & BDC?Working of two-stroke Petrol Engine?Working of two-stroke Diesel Engine?

INTRODUCTION


81


In these engines the working cycle is completed in two strokes of the piston or one revolution of the crankshaft. In case of two-stroke engine the valves replace the ports. Two rows of the ports at different level cut are cut in the cylinder valve. These are known as exhaust port and transfer port due to a specific shape is given to piston crown which helps to prevent the loss of incoming fresh charge being short circuited through the transfer ports and helps the exhausting only the burnt gases.

WORKING OF TWO STROKE PETROL ENGINE


82


The position of the piston at the ends of compression the spark is produced by the spark plug at the piston reached the Top Dead Center. The pressure and temperature of gases increases and the gases push the piston downwards producing the power stroke.

When the piston uncovers the exhaust port during the downward stroke the expands burnt gases leave the cylinder through port.


83


A little later the pistons uncover the transfer port and in this position the crankcase in directly connected top the cylinder through port. During the downward stroke of piston the charge in crank is compressed by the underside of the piston to a pressure of 1.4Kg /cm2Atmosphere. In this piston the compressed charge is transferred through the transfer port to the upper part of the cylinder. The exhaust gases are swept out with the help of fresh charge this piston crown shape helps in sweeping action as well as it prevents the loss of fresh charge carried with the exhaust gases. This is continued until the piston reaches the BDC position. The action of sweeping out the exhaust gases with the help of fresh charge is known as scavenging.


84


The scavenging helps in revoking the burnt gases from the cylinder asThe downward movement of the piston caused the high pressure gases develops powerThe exhaust gases are removed completely from the cylinder by scavengingThe charge is compressed in the crankcase with the help of piston. As the piston moves upward it cover the transferors stopping the flow of fresh charge into the cylinder a little later the piston covers the exhaust ports and actual compression of the charge begins. This position is shown upward motion of the piston during this stroke lower the pressure in the crank case is below atmosphere pressure there fore a fresh charge is induced in the crank case through the inlet port the piston uncovers them .


85


WORKING OF TWO-STROKE DIESEL ENGINEExcept that the fuel is admitted near the TDC the working remains similar to the two-stroke petrol engine the other difference is the scavenging period of two-stroke diesel engine (90degrees) is greater than of petrol engine (70degrees). This is because there is no danger of loss of fuel during scavenging of diesel engine as only air is charged.

USES:-The two stroke petrol engines are generally employed in very light vehicles such as scooters, motor cycles, three wheelers and sprayers.

P-V DIAGRAMS FOR 2-STROKE CYCLES:-FIRST STROKE: -


86


Suppose the piston is at TDC and the volume above the piston (clearance volume) is full of compressed charge (mixture of air–fuel for Otto and only air for diesel cycle). In an Otto cycle the fuel is ignited by means of an electric spark at constant volume, the process2-3. The pressure of hot gases produced due to ignition, moves the piston down –wards and the work by done by the hot gases (process of expansion.) This process continues till the exhaust5 port is open by the piston. During this process the inlet port is closed and the charge already gone to the crankcase is now compressed by the downward motion of the piston. Hence, the inside volume of the case decreases with increase of pressure of the charge. When the exhaust gases in the cylinder is nearly to the atmospheric value, the inlet port opens and the fresh


87


compressed charge from the crankcase enters the cylinder. The first stroke is completed when the piston reaches BDC.

SECOND STROKE: -When the piston moves upwards and the charge is compressed, the inlet port and the exhaust port remain closed. The volume inside the crankcase increases with decrease of pressure and the charge enters in to the crankcase through the inlet port. The second stroke is completed when the piston reaches TDC and the 2-stroke cycle is completed. The p-v diagrams of Otto and Diesel 2-stroke cycles.

ADVANTAGES OF 2-STROKE CYCLE ENGINES: -The advantages of 2-stroke cycle engines over the 4-stroke cycle engines are:


88


A net positive work is obtained from a 2-stroke cycle engine because it works above the atmospheric pressure.They are simple in design, manufacture and operation. Hence, they are used in small power engines such as scooters, auto-rickshaws and motor-cycle.The turning moment of a 2-stroke cycle engines more uniform and a smaller size flywheel is need because of one working stroke for each revolution of the crankshaft.Theoretically, a 2-stroke cycle engine produces twice the power of the 4-stroke cycle engine for the same size and the same speed of the engine because one working stroke in each revolution of the crankshaft is obtained in 2-stroke cycle engine wheels in 4-stroke cycle engines it is obtained in two revolutions of the crankshaft.


89


There is less friction less friction loss due to absence of value rockers, cams and camshafts etc in a 2-stroke cycle engine it is obtained in two revolutions of the crankshaft.There is better scavenging in 2-stroke cycle engine at low speed since the clearance space is not filled by the burnt gases.2-stroke cycle engine is much lighter and more compact for the same as compared to 4-stroke cycle engine.

DISADVANTAGES OF 2-STROKE CYCLE ENGINES: -The following are the disadvantages of 2-stroke cycle engines over the 4-stroke cycle engines:The effective compression ratio is lower in a 2-stroke cycle engine for the same stroke and clearance volume.


90


An effective cooling arrangement is need since there is one working stroke in each revolution and less dissipation of heat than the 4-stroke engine.A 2-stroke cycle engine is noisier because of sudden release of burnt gases in the exhaust port.Mass of lubricating oil needed is more in 2-stroke engines.Scavenging pump absorbs power.Loss of fuel at the time of admission of change in the 2-stroke cycle S.I. engine is observed.Thermal efficiency of 2-stroke engines is generally less due to the fact that some amount of charge escapes without burning and poor scavenging due to short period opening of the exhaust port.

QUESTION BANK


91


Describe the working of 2 stroke petrol engine.Describe the working of 2 stroke diesel engine.

EXPERIMENT NO:10


92


FOUR STROKE PETROL AND DIESEL ENGINE

AIMTo study the four stroke Petrol and Diesel engine.

LEARNING OBJECTIVESWorking of four-stroke petrol engine.Working of four stroke Diesel engine.

INTRODUCTIONIn these engines the working cycle is completed in four strokes of the piston or two revolution of the crankshaft.

WORKING OF FOUR STROKE PETROL ENGINE

Suction stroke


93


The piston is at TDC and is ready to move down drawing its mixture of fuel and air at this time the inlet valve is open and exhaust valve is close as the piston moves downward a fresh charge of fuel air mixture enters the cylinder through the inlet valve due to the suction created. This reaches until piston reaches BDC at this position the inlet valve close and the downward movement of the piston if known as suction stroke and crank rotates by 180 degrees during the period.

2) Compression strokeDuring this stroke both valves are closed and piston moves upward and compressed the charge enclosed in the cylinder and the pressure as well as temperature increases as the piston reaches TDC, the mixture is ignited by and electric spark.


94


3) Power or expansion stroke:The increased pressure of mixture exerts a large force and pushes the pistons during the expansion stroke. Both valves remain closed the high pressure and temperature gases pushes the piston downwards and the gas pressure gradually decreases from TDC to BDC.

4) Exhaust stroke:


95


During the upward motion of piston the exhaust valve is open and inlet valve is closed. The piston moves up in the cylinder pushing out the burnt gases through the exhaust valves as the piston reaches the TDC again the inlet valve is open and fresh charge is taken during next downward movement and cycle is repeated. The engine is known as four-stroke petrol engine and in this engine the working cycle is completed in four strokes of the piston or two revolution of the crankshaft.COMPARISION OF SI & CI ENGINES

Description SI Engine (Petrol engine) CI engine (Diesel engine)1) Basic type Otto cycle

Diesel cycle2) Fuel used Gasoline

Diesel oil


96


3) Introduction of fuel Carburetor is used Fuel & injector’s isused4) Ignition Spark ignition

Self ignition due tohigh compression5) Compression ratio 6 to 10

16 to 206) Speed High speed engines Low speed engines7) Thermal efficiency Lower

Higher8) Weight Lighter

Heavier

WORKING OF FOUR STROKE DIESEL ENGINE

The working cycle of the engine is completed in four strokes and diesel oil is used as fuel.Suction stroke


97


The suction is similar to petrol engine except that instead of fuel air mixture only air is taken n the cylinderCompression stroke:The temperature of air is comparatively higher due greater compression ratio. And is about 60 Kg /cm2 and 600 degrees respectivelyExpansion stroke:The inlet and outlet valves are closed fuel in injected by nozzle just at the beginning of the stroke as soon as the fuel is injected due to high pressure and high temperature fuel takes fire and due to this combustion air expands and the piston moves downwards and work is done.4) Exhaust stroke:


98


During the upward motion of piston the exhaust valve is open and inlet valve is closed. The piston moves up in the cylinder pushing out the burnt gases through the exhaust valves as the piston reaches the TDC again the inlet valve is open and fresh charge is taken during next downward movement and cycle is repeated. The engine is known as four-stroke petrol engine and in this engine the working cycle is completed in four strokes of the piston or two revolution of the crankshaft.

QUESTION BANK

Describe the working of 2 stroke petrol engine?Describe the working of 2 stroke diesel engine?


99


Compare 4 – stroke & 2-stroke cycle Engines?Define bore, stroke, displacement, volume, clearance volume and compression ration?What do you mean by TDC &BDC?Explain the P-V Diagram for SI &CI engines?


100

Thermodynamics Lab Manual

Documents

good boiler

cornish boiler

cochran boiler

lamont boiler

benson boiler

boiler shell

velox boiler

stirling boiler