nmu fe engg thermodynamics 2011

R.C.P.I.T, Shirpur Department of Mechanical Engineering

Engineering Thermodynamics 1

Laboratory Report

Experiment No 1

Batch Code: _____________

Name of Student: _________________________________________ Roll No. ____________

Date of Lab: ___________________ Date of Submission: _________________ Evaluations 1) Lab Attendance [4]

a) Pre lab work done (if any) [1] ___________

b) Submission of Report (on Lab date) [2] ___________

c) Records of Lab Notebook [1] ___________ 2) Observations and Conclusion [3] ___________ 3) Oral [3] ___________ Overall Marks ___________

________________________________ _______________________ Lab Instructor Sign of Subject Teacher



AIM: Study of Two- stroke petrol and diesel engine. INTRODUCTION: Heat engine is an energy conversion device in which heat energy is converted in to mechanical energy. Heat engines are generally classified as internal combustion engines and external combustion engine, either by the manner in which combustion of the fuel takes place the combustion chamber or in separate unit placed outside respectively. Internal combustion engine is therefore, a heat engine in which combustion of the fuel takes place inside the cylinder. CLASSIFICATION OF INTERNAL COMBUSTION ENGINE: 1. Type of fuel used a. Petrol or gasoline engine b. Diesel engine c. Gas engine 2. Types of ignition used a. spark ignition (SI) b. compression ignition (CI) 3. Number of strokes per cycle a. four stroke engine b. two stroke engine 4. According to the no. of cylinders a. single cylinder b. multi cylinder 5. Arrangement of cylinder a. vertical engine b. horizontal engine c. radial engine d. V- engine 6. Type of cooling system a. air cooled engine b. water cooled engine 7. Type of speed a. low speed engine b. medium speed engine c. high speed engine 8. Type of application a. stationary engine b. automotive engine c. marine engine d. aircraft engine e. locomotive engine Working principle of two-stroke petrol engine: The two stroke engine requires one revolution of crankshaft or two strokes of the piston to complete the cycle of events (suction, compression, power, and exhaust) Figure shows working principle of two-stroke petrol engine. First stroke: Assume that piston is at BDC position. During this stroke, the piston moves upwards from BDC to TDC. It closes the transfer port and the exhaust port. The charged air fuel mixture that



is already there in the cylinder is compressed. Due to upward movement of the piston, a partial vacuum is created in the crankcase and the fresh charge is drawn in to the crank case through the uncovered inlet port. At the end of this stroke, the piston reaches the TDC position. Second stroke: The compressed charge ignites in the combustion chamber by means of an electric spark produced by the spark plug, slightly before the completion of the compression stroke .Due to combustion piston is moved downward direction. During this stroke, the piston covers the inlet port and the fresh charge is compressed in the crank case. Further downward movement of the piston uncovers the exhaust port and then transfer port. The expanded gases start escaping through the exhaust port and at the same time fresh charge which is already compressed in the crank case, is forced into the cylinder through the transfer port. The charge strikes the deflector on the piston crown, rises to the top of the cylinder and pushes out most of the exhaust gases. The piston is now at the BDC position. The cylinder is completely filled with the charge. The cycle of events is then repeated. Working principle of two stroke diesel engine: The two stroke diesel engine works as that of the petrol engine but it injects diesel at end of compression stroke. The working principle is given below: As the piston moves down on the power stroke, it first uncovers the exhaust port and the cylinder pressure drops to atmospheric pressure as the products of combustion come out from the cylinder. Further downward movement of the piston uncovers the transfer port and slightly compressed air enters the engine cylinder from the crank case. Due to the deflector on the top of the piston, the air will move up to the top of the cylinder and expels out the remaining exhaust gases through the exhaust port. During the upward movement of the piston, first the transfer port and then the exhaust port closes. As soon as the exhaust port closes, the compression of the air starts. As the piston moves up, the pressure in the crankcase decreases so that the fresh air is drawn into the crankcase through the open inlet port as shown in fig. Just before the end of the compression stroke, the fuel is forced under pressure in the form of fine spray into the engine cylinder through the nozzle into this hot air. At this moment, the temperature of the compressed air is high enough to ignite the fuel. It suddenly increases the pressure and the temperature of the products of combustion. The rate of fuel injection is such as to maintain the gas pressure constant during the combustion period. Due to increased pressure the piston is pushed down with a great force. Then the hot products of combustion expand. During expansion some of the heat energy produced is transformed in to mechanical work. When the piston is near the bottom of the stroke it uncovers the exhaust ports, which permits the gases to flow out of the cylinder. This completes the cycle and the engine cylinder is ready to suck the air once again.



Table 1.1 Differences between petrol and diesel engine:

Comparison Petrol engine Diesel engine Inventors Augustus Otto Dr .Rudolf diesel Fuel used petrol diesel Intake into the cylinder Petrol + air mixture Only air ignition Spark ignition (SI) makes use

of fuel and air mixture. Compression ignition (CI)) Makes use of the fuel

Thermal efficiency Less thermal efficiency 25% Higher thermal efficiency 30 to 36%

Speed High speed 500 to 700 rpm Speed limited to 2400 rpm Compression ratio Lower compression ratios 4:1

to 10:1 Higher compression ratios 12:1 to 22:1

Compression pressure 15-20 bar 30-40 bar Life Less life Longer life than equivalent

to petrol engine Construction Strong and light parts More robust construction of

parts. Stronger and heavier parts.

Fuel supply Uses carburetor and spark plug

Uses fuel injection pump and nozzle injector.

Cost Less initial cost More initial cost Running cost High running cost Less running cost

Lab Activity: Group Discussion:

Students should discuss among themselves what IC engine, its types is and real life applications. Give at least FIVE examples each of two stroke Petrol & diesel engines used like in cars, bikes, agriculture, etc. Discuss above comparison of two stroke Petrol & diesel engine using any two such examples.



Laboratory Report

Experiment No 2

Batch Code: __________________



a) Pre lab work done (if any) [1] _ _________






AIM: Study of Four stroke petrol and diesel engine. Working of 4 strokes -Petrol engine: In four-stroke engine all the events i.e. suction, compression, power and exhaust are completed in two revolutions of crankshaft. They are described below: 1) Suction stroke: The stroke begins when the piston is at top dead center (TDC).The piston moves downward. The inlet valve opens. A mixture of petrol and air vapors, mixed proportionately by the carburetor enters the cylinder and fills the space in the cylinder. The piston reaches its lowest position known as bottom dead center (BDC). 2) Compression stroke: The piston moves up after the intake stroke. The inlet valve closes when the piston moves upward .The exhaust valve also remains closed the piston compresses the fuel air mixture by pushing it upward into clearance space at the top of the cylinder. Pressure and temperature of the mixture increases during compression. 3) Power stroke: A spark ignites the fuel air mixture at high pressure and temperature. The spark ignites the fuel air mixture. This burning increases the pressure and temperature of the gases further. The gases expand producing an explosive force pushing the piston down. Piston moves down at high acceleration. The piston is connected to the connecting rod. The connecting rod is attached to crankshaft. The linear movement of the piston is converted into rotary motion of the crankshaft. 4) Exhaust stroke: The piston reaches the bottom centre at the end of the power stroke the exhaust valve opens. The burnt gases escape at greater speed. The piston moves up from bottom centre and pushes out the remaining burnt gases inside the cylinder. At the end of the exhaust stroke the exhaust valve closes. The cycle is repeated for every four stroke of the piston the crankshaft rotates 2 revolutions. Working of 4stroke- diesel engine: 1) Suction stroke: Suction stroke is the first stroke. Piston moves down the inlet valve is open, allows air to enter the cylinder, and fills the space. Piston reaches the BDC and again starts moving up. 2) Compression stroke: The piston starts moving up. The inlet valve is closed air is compressed. The pressure and temperature of the air increase due to compression. Just before the piston reaching TDC. Diesel fuel is sprayed inside the cylinder. The fuel is sprayed by means of fuel injector. The fuel is sprayed at very high pressure overcoming the pressure of compressed air. The fuel gets mixed up with the air the air contains oxygen. Since the fuel is hydrocarbon, the temperature of compressed air is sufficient to initiate the combustion. The fuel burns. 3) Power stroke: The piston moves from TDC to BDC. The heat released by combustion increases the pressure and temperature of the air further. The maximum pressure and temperature of the burnt gases act on the top of the piston and forces the piston to move fast, accelerates the piston downwards. This is the power stroke just before the piston reaches the BDC the inlet valve is opened. Thus, the cycle repeats.



4) Exhaust stroke: The piston reaches the BDC and starts moving up the burnt gases are being pushed out by the piston. The gases escape through exhaust valve before the piston reaches TDC the inlet valve is opened the cycle is repeated. Table 2.1 Differences between four strokes and two stroke cycle engines:

Sr.no. Four stroke cycle Two stroke cycle 1 The cycle completes in four strokes of

the piston or in two revolutions of crankshaft.

The cycle completes in two strokes of the piston or in one revolution of crankshaft.

2 It needs a heavier flywheel. It needs a lighter flywheel. 3 Power produced for same size of engine

is small or for the same power, the engine is heavy and bulky.

Power produced for same size of engine is more or for the same power the engine is lighter and compact.

4 Cooling and lubrication requirements are low.

Greater cooling and lubrication requirement wear and tear is more.

5 Low wear and tear of engine parts. More wear and tear of engine parts. 6 The four-stroke engine contains valves

and valve mechanism. Two stroke engines have no valves but only ports.

7 Higher initial cost. Due to the absence of valve mechanism cheap initial cost.

8 Thermal efficiency is higher. Thermal efficiency is lower. 9 Used where efficiency is important (e.g.

cars, buses) Used where low cost, compactness and light weight important.(e.g. Scooters, motorcycles)

Lab Activity: Group Discussion:

Students should discuss among themselves what IC engine, its types is and real life applications. Give at least FIVE examples each of four stroke Petrol & diesel engines used like in cars, bikes, agriculture, etc. Discuss above comparison of four stroke Petrol & diesel engine using any two such examples.



Laboratory Report

Experiment No 3

Batch Code: __________________

Name of Student: ____________________________________________ Roll No. ____________

Date of Lab: ______________________ Date of Submission: ____________________

Evaluations

1) Lab Attendance [4]

a) Pre lab work done (if any) [1]____

b) Submission of Report (on Lab date)[2]___________

c) Records of Lab Notebook [1] ___________

2) Observations and Conclusion [3] ___________

3) Oral [3] ___________

Overall Marks ___________

________________________________ _______________________

Lab Instructor Sign of Subject Teacher



AIM: Study of Babcock and Wilcox Boiler. Introduction of Boiler: A steam generator also known as Boiler, is a closed vessel in which the water is converted into steam by the application of heat. The heat is produced by burning the fuel which are commonly used in boiler are coal, oil and gas .The steam generated by the boiler is used in various industries for processing, heating and for running steam turbines in power plant. Application: 1. The steam is used to drive prime movers likes steam engine or steam turbine which drives an electric generator to produce electricity. 2. The steam may be supplied at low pressures for the process industries like cotton mills, sugar factories. 3. Steam is also used for heating residential and industrial building in water. 4. The steam produced in the boiler is used for producing hot water, which can be used for heating at much lower pressures. Selection of a Steam Boiler: Engineers consider following factors for selecting the size and type of a steam boiler: 1. The power required and the working pressure. 2. The rate at which the steam is generated. 3. Availability of fuel, water and transport. 4. The geographical position of the powerhouse. 5. The type of fuel used. Classification of Boiler: 1. According to the method of Heating: a. Fire Tube Boiler b. Water Tube Boiler In Fire Tube Boiler the hot gases produced by the combustion of fuel passes through the tubes, which are surrounded by water. The heat from hot gases is conducted through the walls of the tubes to the surrounded water Example of the fire tube boiler are simple vertical Boiler, Cochran Boiler, Lancashire Boiler and Locomotive Boiler . In water Tube boiler, the water flows inside the tubes (called water tubes) which are surrounded by flames and hot gas from outside Example of the water tube boiler are Babcock and Wilcox boiler, La-Mount Boiler, Benson boiler and Loeffler boiler. 2 According to firing method: a. Internally fired boiler b Externally fired boiler 3 According to the axis of the shell: a Vertical boiler b Horizontal boiler 4 According to the method of method of circulation of water and steam: a Natural circulation Boiler b Mobile Boiler



Babcock and Wilcox Boiler: Description: It is stationary water tube boiler. It consists of steam-water drum. Uptake header and down take header are attached with steam-water drum, as shown in figure. Each header is provided with hand hole in the front of the tubes and it is covered with caps. A mud box is provided with each down space header and the mud collected, is removed. There is a slow moving automatic chain on which the coal is fed from the hopper. The firebricks baffles wall deflects the hot gases and helps the hot gases to leave the chimney and a pulley. Working: Coal is fed to the grate through the fire door. The hot flue gases rise upward and pass across the left side portion of the water tubes. The baffles deflect the flue gases and hence the flue gases travel in a zigzag manner over the water tubes and along the super heater. The flue gases finally escape to the atmosphere through the chimney. Water circulation : The portion of the water tubes which tubes are just above the furnace are heated comparatively to higher temperature than the rest of it. Water raises into the drum the uptake header. Here the steam and water are separated in the drum .Steam is lighter, is being collected in the upper part of the drum. The water from the drum comes down through the down header into the water tube. A continuous circulation water from the drum to the water tube and vice versa is thus maintained .The circulation water is maintained by convective current and is known as “Natural circulation”. Superheating: Steam is taken from the steam space through a tube to the heater. Steam is super heated. Function of boiler Fitting and Accessories: The boiler is fitted with necessary mountings. Pressure gauge and water level indicator are mounted on the boiler at its left end. Steam safety valve and stop valve are mounted on the top of the drum, Blow-off cock is provided fir the periodical removal of mud and sediment collected in the mud box.



Table 3.1 Difference between Fire tube boiler and Water tube boiler:

Sr no

Particular Fire tube Boiler Water Tube Boiler

1 Position of water and hot gases Hot gases inside the tubes and water outside the tubes

Water inside the tubes and gases outside the tubes

2 Mode of Firing Generally internally fired

Externally fired

3 Operating pressure Limited to 16 bar Can work under as high pressure as 100 bar

4 Rate of steam production Lower Higher

5 Suitability Not suitable for large power plants

Suitable for large power plants

6 Risk of bursting Involves lesser risk on explosion due to lower pressure

Involves more risk on bursting due to high pressure

7 Floor area For a given power it occupies more floor area

For a given power it occupies less floor area

8 Construction Complex Easy 9 Transportation Difficult Simple 10 Shell Diameter per unit power Large Small 11 Chances of Explosion Low High

12 Requirement of skill Requires less skill for efficient and economic working

Requires more skill and careful attention

The water Tube boiler are used exclusively, when pressure above 10 bar and capacity in excess of 7000Kg of steam per hour is required .Babcock and Wilcox water tube boiler is an example of horizontal straight tube boiler and may be designed for stationary or marine purposes. The technical specifications of this boiler are given below:

Diameter of the drum : 1.22 to 1.83 m Length : 6.096 to 9.144m Size of the water tube : 7.62 to 10.16 cm Size of super heater tube : 3.84 to 5.71cm Working pressure : 40 bar(max) Steaming capacity : 40000kg/hr (max) Efficiency : 60 to 80 %

Lab Activity: Group Discussion: Students should discuss among themselves what boiler is, its types and its applications.

Discuss using chart / model construction & working of boilers. Can you show how combustion products / water and steam flow inside the boiler?



Laboratory Report

Experiment No 4

Batch Code: __________________









AIM: STUDY OF COCHRAN AND LANCASHIRE BOILER. Introduction of boiler: A steam generator also known as boiler. It is closed vessel in which the water is converted into steam by application of heat .The heat is produced by burning the fuel which are commonly used in boiler are coal, oil gas The steam generated by the boiler used in various industries for processing heating add for running steam turbine in power plant. FIRE TUBE BOILER: Cochran boiler: It is one of the best types of vertical multi-tubular boiler and has a number of horizontal fire tubes. It consists of a cylindrical shell with a dome shaped top where the space is provided for steam. The furnace is one piece construction and is seamless its crown has a hemi spherical shape and thus provided maximum volume of space .The fuel is burnt on the grate and as is collected and disposed of from ash pit. The gases of combustion produced by burning of fuel enter in the combustion chamber through the flue tube and strike against firebrick lining which directs them to pass through number horizontal tubes, which are immersed in water. After which the gas escape to the atmosphere through smoke box and chimney a number of hand –holes are provided around the outer shell for cleaning purpose. The various boiler mounting are shown in figure and are water level gauge safety valve, steam stop valve, blow of cock, manhole and pressure gauge. Arrows indicate the path of combustion gases and that of circulating water. The technical specifications of Cochran boiler are given below:

Shell diameter : 2.75m Height : 5.79m Working pressure : 6.5bar (max.pressure15bar) Steam capacity : 3500kg/hr (max.capacity 4000kg/hr) Heating surface : 120m2 Efficiency : 70 to 75 %( depending on the fuel used)

LANCASHIRE BOILER : It is a horizontal, internally fired, fire tube; stationary boiler .The boiler has cylindrical shell usually 2 to 3 m in diameter and 7 to 9m long. This boiler is used for power generation at moderate steam pressure of 15bar. The boiler consists of a large shell supported by refractory brick masonry. Two large, horizontal and parallel flue gas tubes are passing through shell .The fire place is located in front of flue tubes. In brick work , a flue passage A below the boiler shell Two passage B and C at the sides of sides of boiler are formed The flue passage B and C are connected to a chamber and then to chimney. The fuel is burnt at the grating and the hot gases travel along internal flue tubes followed by the flue passage A and then side passage B and C the flue gases are them collected in the chamber before they lead to atmosphere through a chimney. The hot flue gases transfer its maximum heat contents to water during it long passage. The water is converted into steam and collected in the steam space in the shell and it is then taken out through steam stop valve for use. The boiler is also provided with usual mounting like pressure gauge, Blow of cock, steam stop valve and safety valve. It is also provided with low water and high steam alarm, which gives audio signal for low water level high steam pressure. Lab Activity:

Discuss using chart / model construction & working of boilers. Can you show how combustion products / water and steam flow inside the boiler?



Laboratory Report

Experiment No 5

Batch Code: __________________









AIM: Study of Air compressor. Introduction: Air compressor also known as air pump is machine that takes in atmosphere air compressor. It decreases the volume and increases the pressure of air possess great potential energy ,because when the external pressure is removed, the air is used in many ways and provides the motive force for air motors and tools including pneumatic hammer ,air drills ,sand blasting machine and point sprayers . Used of compressed Air: The compressed air has wide application in industries as well as in commercial equipment.

1. Compressed air is used in air refrigerator and cooling of large building. 2. Compressed air is used for driving pneumatic tools in shop like drills, riveter screw driver

etc. 3. Compressed air is used for driving air motors in mine, where electric motor and I.C engine

cannot be used because of fire risks due to the pressures of inflammable gases etc. 4. Compressed air is used for clearing purpose. 5. Compressed air is used in blast furnace. 6. Compressed air is used in spray painting. 7. Compressed air is used for hard excavation work, tunneling, boring. 8. Compressed air is used for starting for heavy duty diesel engine. 9. Compressed air is used for operating air brakes on buses, trucks and train. 10. Compressed air is used to inflate automobile or aircraft tyres. 11. Compressed air is used to supercharge the internal combustion engine 12. Compressed air is used in gas power plant operation. 13. It is used for conveying solid and powered material in pipe line. 14. It is also used in automobile suspension system.

Compressor Types: Compressors are classified as: Positive displacement compressor and Dynamic compressor Positive displacement compressor increases the pressure of the gas by reducing the volume. They are further classified as reciprocating and rotary compressor. Dynamic compressors increase the air velocity ,which is then converted into increased pressure at the outlet .Dynamic compressor are basically centrifugal compressor & further classified as radial and axial flow types. The flow and pressure requirement of the given application determine the suitability of a given particular type of compressor. Figure 5.1 Classification of Compressors:



POSITIVE DISPLACEMENT COMPRESSOR: RECIPROCTAING AIR COMPRESSOR A machine which takes in air or gas during suction stroke at low pressure and then compresses it to high pressure in a piston –cylinder arrangement is known as reciprocating compressor. External work must be supplied to the compressor to achieve required compression. A part of the work supplied to the compressor is lost to the overcome the frictional force between rubbing surface of piston and cylinder .The cylinder of air compressor is cooled to minimize the work input. Every 40C rise in inlet air temp result in a higher energy consumption by 1% to achieve equivalent output. Hence cool air intake leads to a more efficient compression. Working principle of reciprocating air compressor: A reciprocating compressor consist of a cylinder, piston inlet and outlet valves. The valves used are of seed type, balanced by pressure on either side. During the downward motion of the piston the pressure inside the cylinder falls below the atmospheric pressure. Thus atmospheric air enter the cylinder until the piston reaches the bottom dead centre. As the piston start moving upward the pressure of air in the cylinder increases and when it become equal to the atmospheric pressure the inlet valve close The air trapped inside the cylinder is compressed and the pressure start increasing continuously until the pressure inside the cylinder exceed the pressure on delivery valve. Then the delivery valve open and air is delivered to the receiver during remaining upward movement of the piston at the end of delivery stroke, small volume of the high pressure air left in the clearance space .The high pressure air left in the clearance space expands as the piston start moving downward and the pressure of the air fall until it just below the atmospheric pressure. The inlet valve open and atmospheric air is taken in for next cycle suction, compression and delivery of the air takes place with two strokes of the piston of one revolution of the crank. ROOTS BLOWER: Roots blowers are positive displacement rotary machine. They have casing with inlet and outlet passage of air. They have three or more lobed impeller. The lobed impeller rotates by gear in external housing. The air is drawn into the casing with movement of loaded impellers and trapped when impeller tape touches the casing The air is compressed by squeezing action and then discharged thru. the opening . VANE COMPRESSOR: It consists of a set of spring loaded vanes. The rotor is in eccentric disc. The air at atmospheric pressure is trapped between the vane, when rotation is given to the rotor. The rotor moves in anticlockwise direction. The one vane trapped the air and compresses it till it delivers. As blade moves past the inlet passage compression begins. Due to decreasing volume is delivered with arrival of each blade at the delivery passage. CENTRIFUGAL COMPRESSOR : It is dynamic action rotary compressor .It consists of an impeller with a series of radial curved vane diffuser and casing as shown in fig. The air enters axially in to the impeller eye it comes out radially. The velocity of the impeller increases the momentum of air, causing rise in pressure and temp. air leaving the impeller enter in the diffuser passage where it kinetic energy is converted into pressure energy. Thus pressure of air further increased. The air is then collected in the casing and discharged from the outlet of the compressor. A pressure ratio of 4 can be obtained in single stage centrifugal air compressor .



AXIAL FLOW COMPRESSOR; In axial flow compressor, the air flow parallel to the axis of the machine it consist of large no. of rotating blade rows, fixed on the rotating drum and starter blades, fixed on the casing of the compressor as shown fig .Each state consists of fixed one row moving blade and one row of fixed blade. The blade made of recoil sexton to reduce the losses caused by turbulence and boundary separation. The work input to the rotor shaft is transferred to the moving blade to air to accelerate it. The blades are so arranged that the spaces between the blade from the diffuser passage. The air then further diffused in stator blade which are also arranged to from the diffuser passage. The fixed blade also helps to guide the dir into the next stage of moving blade to reduce the losses caused by stock. The type of compressor can give pressure ratio of 1:2 or 1:3 per stage. The no. of stages used in this type compressor varies 4 to 16. Lab Activity:

Discuss using chart / model construction & working of different compressors. List various applications of respective types of compressors.



Laboratory Report

Experiment No 6

Batch Code: __________________

Name of Student: ____________________________________________ Roll No. ____________

Date of Lab: ______________________ Date of Submission: ____________________

Evaluations

1) Lab Attendance [4]

a) Pre lab work done (if any) [1]____

b) Submission of Report (on Lab date)[2]___________

c) Records of Lab Notebook [1] ___________

2) Observations and Conclusion [3] ___________

3) Oral [3] ___________

Overall Marks ___________

________________________________ _______________________

Lab Instructor Sign of Subject Teacher



AIM: Study of household refrigerator and room air conditioner. Introduction: A refrigerator is a device which removes heat from a body at low temperature and rejects it to a body at high temperature usually atmosphere. Refrigeration is a process of producing and maintaining temp. of system or space below temp. of surrounding. Thermodynamic principle: Refrigeration process is an example of second law of thermodynamics Claussius statement. “It is impossible to construct a device which when operating in a cycle will produce no effect other than the transfer of heat from a cooler to hotter body.” In a refrigeration process, heat is being continuously pumped from low temp. space and is rejected at high temperature space. External power is required to carry out this process. Therefore refrigerating system is power absorbing system. Necessity of household refrigerator: Mainly it is used for preserving foods, fruits etc. which would otherwise be spoiled in short time particularly in hot season because food destroying microorganism grow much faster generally 1000 times at 10ºC than at 4ºC. Unit of refrigeration: Refrigerating effect is measure in Ton. 1 ton of refrigerating effect means amount of heat abstracted from 0ºC water in 24 hrs for producing 1 ton of ice at 0ºC. 1 ton effect = 210 kJ/min = 50 kcal/min. Types of refrigeration: Conventional refrigeration systems are: 1. Air refrigeration system 2. Vapour refrigeration system a. Vapour compression refrigeration b. Vapour absorption refrigeration Non – conventional refrigeration system are: 1. Thermo electric refrigeration system 2. Vortex flow refrigeration system. “All domestic or household refrigerators are vapour compression refrigerators.” Main components of vapour compression refrigerator: 1. Hermetically sealed compressor. 2. Condenser 3. Expansion device 4. Evaporator. Constructional details: All domestic refrigerators have a cabinet shape. In its basement hermetically sealed compressor is located .Electric motor and reciprocating compressor are enclosed in a single casing to avoid refrigerant leakage. All natural circulation refrigerators have a condenser coil. It is equipped with number of pin fins to improve the amount of heat removal from refrigerant and arranged at the back side of the cabinet. A simple capillary tube is used as a throttling device. The evaporator coil remains exposed in the storage cabinet at the top portion of the cabinet. To avoid excess frost formation, an auto defrost button is located at the centre of the thermostat. When you



press, button, defrosting takes place automatically and water evaporates by itself, when preset temperature reaches, refrigerator restarts automatically. Refrigeration cycle: The working substance of refrigeration system is known as refrigerant. Freon 12 is used in domestic refrigerators because it is non toxic and non inflammable. When refrigerators start, electric motor runs the compressor. It sucks the low pressure refrigerant vapour from evaporator coil and delivers high pressure, high temperature refrigerant system. Process and description (see fig.) a-b: refrigerant slightly superheated and at low pressure is compressed in the compressor. The pressure and temperature of refrigerant is raised. b-c: the refrigerant in the superheated vapour state then passes through the condenser. The circulating water in the condenser removes heat from the compressed vapour and due to this heat removal, vapour gets condensed. The vapour is at high pressure. c-d: the condensed liquid at high pressure expands through throttle valve. The pressure and temperature of fluid is reduced. A portion of liquid refrigerant is converted into vapour. d-a : the refrigerant which is mixture of liquid and vapour at low pressure and temperature, enters the evaporator. Here it takes heat from the space or body to be cooled. The heat so extracted is utilized in evaporating the liquid portion of refrigerant. The evaporated refrigerant which is slightly superheated then enters the compressor. Application of refrigeration system: 1. It is used for making ice, preservation of food. 2. It is used to cool water. 3. It is used in cold storage, comport air conditioning, different industrial processing. etc. Specifications: Household refrigerator. Make :Voltas limited Capacity: 165 liter, compressor 1/8 HP Weight : 43 kg, external dimension Width : 550mm Depth : 605 mm Height : 1070 mm Room air conditioner: Room air conditioner and its purpose: Air conditioning is the technique of simultaneous control of temperature, humidity, motion and purity of atmosphere in a confined space. Thus the main purpose of A. C. system is to control the temperature, humidity and movement of air in order to: 1. Promote human health and comfort. 2. Improve human efficiency and working conditions. 3. Keep the material and the products in most natural state while in storage or under production or

manufacturing processes. Room air conditioner: It is the simple type of A. C. unit made as an enclosed assembly in the factory. It is designed as a unit meant for mounting in a window or through a wall. It does not require ducts for free delivery air to space. The unit is divided into two parts: 1. Indoor part 2. Outdoor part

The indoor part includes a filter evaporator, a motor driven fan or a blower and expansion device. The outdoor portion includes a hermetical sealed motor compressor unit, condenser and a motor driven fan.



A fan is used to force outside air over the condenser coil to remove the heat from condenser coil. In order to draw air through filter and force it over the evaporator coil to cool the atmospheric air, another fan is provided in the indoor portion. For driving the two fans either same motor or a separate motor is used for driving each of the fans. The room air conditioner works on the principle of vapor compression refrigeration system. Some of the important features of air conditioner are:

1. cooling capacity : 1/

2 to 1 1/2 tons

2. power range : 3/4 to 2 HP

3. discharge velocity : 100 to 400 meters/min (In case of rooms, where people are at rest, low velocity of air is preferred. The direction of flow can be controlled.)

4. Temperature control : by means of built in thermostat compressor. 5. Condenser is air cooled.



Unit wise list of theory questions from University Exams

Unit I Basic concepts and Fundamentals Marks

Basic

concepts

What is Engineering thermodynamics? State its scope/significance. 4

Define following terms: Heat, energy, Pressure, Thermometric property

State, Path, Process, Property,

Flow system, Non Flow system, Isolated system, Thermodynamic system, surroundings, control

volume,

2 marks

each

What do you understand by Macroscopic & Microscopic Point of view? 6

Explain: a) Classical and Statistical Thermodynamics.

b) State Function And Path Function

3 each

Define thermodynamic system. Explain types of system with suitable examples and sketches. 6

Explain the following terms with examples: - Open system, Closed System 4

Explain control Mass system & Control Volume System with 2 examples of each. 6

Explain property & non property. Give 2 examples of each. Discuss “Property is an exact

differential.”

4

What is the difference between intensive and extensive properties? 4

What do you understand by thermodynamic equilibrium? 4, 6

What do you mean by thermal equilibrium? 2

Define and explain Quasi Static Process. 3, 4

Explain Reversible & Irreversible Processes. 6

Pressure,

temperature

Explain the pressure measurement using Bourdon’s Gauge. 8

How pressure measurement is done? Write a note on Bourdon’s Pressure gauge. 10

State Zeroth law of thermodynamics. 2

State & explain (Justify) Zeroth law Of Thermodynamics used as a base for temperature

measurement.

4.6

Explain Constant Volume gas thermometer. 3

Energy,

Work, Heat

Define internal energy. Prove that it’s the property of a system. 6

What is low grade & high grade energy. 4

Write the sign convention for heat transfer & work transfer. Discuss the similarity between heat

and work.

4

When work is is said to be done by the system? 3

How does the current flowing through a resistor represent work transfer? 4

Differentiate between Thermodynamic work & mechanical Work. 4

Unit II 1st

law of Thermodynamics Marks

1st

law,

PMM-I

Explain Joule’s experiment with a neat sketch. 5

Explain 1st law of thermodynamics with the help of Joule’s experiment. 5

Explain 1st law of thermodynamics with the help of suitable examples. 8

State and explain 1st

law of thermodynamics for a closed system undergoing a cycle. 10

State the significance of PMM-I. 3

IE, -vdp

work

Define internal energy. Prove that it’s the property of a system. 4, 6

Prove:”Internal energy is the function of temperature only”. 5

Explain the significance of � −�� . 6

Explain the significance of –ƒPdv in case of Steady Flow & Non Steady Flow Process. 7

Show for a steady flow system, Work done =� −�� when changes in KE & PE are neglected. 6

Define specific heat under constant pressure & under constant volume for an ideal gas. 4

SFEE

Prove : Cp-Cv=R. 4, 6, 8

Define steady flow process. Derive Steady Flow Energy Equation. 4

Derive an energy equation on Time basis for a Steady Flow process. 6

Apply SFEE for the following applications with suitable assumptions : 3 mark

each a) nozzle, turbine, compressor, pump.

b) nozzle, water turbine, throttle valve, water pump.

c) nozzle, water turbine, steam turbine, centrifugal pump.

Derive Continuity Equation. 3



Unit III 2nd

Law of Thermodynamics Marks

2nd

law

What are the limitations of 1st

law of thermodynamics? Explain with examples. 4

Give statements of 2nd law of thermodynamics. 2, 4

State Kelvin Plank and Clausius statement of thermodynamics. Prove their equivalence. 6, 8

Explain-“Violation of Clausius Statement leads to the violation of Kelvin Plank Statement.”

HE, HP, R

State and prove Carnot theorem. 8

Explain Refrigerator using a neat sketch. 6

What is Coefficient of Performance? Prove: COPHP = COPR +1. 4

Reversibility

Explain Reversibility & Irreversibility. Discuss causes of irreversibility of a process.

6

Discuss causes of irreversibility & justify using Iind law that the free expansion procee is

irreversible one.

8

Entropy

Define entropy & prove that it is a property of system. 6, 8

State & prove Clausius Inequality. 6, 10

Prove: Two isentropic lines can never intersect each other. 4, 6

State & Prove Clausius Theorem. 6, 10

Carnot Cycle

Explain Carnot Cycle with P-V & T-S diagram. 6

Explain Carnot Cycle in detail & derive relation for efficiency in terms of temperatures. 8

Unit IV Ideal Gas Process Marks

Gas Laws

Explain terms: - Universal Gas Constant, Ideal Gas. 4

What is an ideal gas? Derive the ideal gas equation. 4

Derive Equation of State for an ideal gas. 4, 10

Derive the Characteristic gas equation for a perfect gas. 6, 10

Show that for an Ideal gas, the slope of a constant volume line on T-S diagram is more than that

of a constant pressure line.

6

State: Dalton’s law of Partial Pressures, Avogadro’s law, Boyle’s law, Charles law 2 each

Define: Avogadro’s Number, Molar volume, Mole of a gas 4

Define Cp and Cv. 4

Prove: For an Ideal Gas, Cp-Cv=R 4, 8

Gas Process

Draw ∫Pdv work of various Quasi Static processes under P-V & T-S diagrams. 6

Briefly explain following processes:- Constant Volume Heating/Cooling, Constant pressure

heating, Isentropic expansion process.

6

Draw p-V and T-s plane for- isobaric, isochoric and hyperbolic processes. 6

Explain enthalpy is a function of temperature only. 4

What is polytropic Specific Heat? Derive its relation. 6

Derive an expression for Heat transfer during a polytropic process. 6

What is a polytropic process? Show it on p-V diagram. Write its work done equation. Derive

equation for heat supplied during a polytropic process.

10

Prove: For a polytropic process, ��

��=

��

��

(� �

�)

4

Isentropic

Derive expressions for the work done and Heat supplied during Adiabatic Process. 6

What is an Adiabatic Process. Show it on P-V & T-S diagrams. Derive an expression of work done

during the process.

10

Prove that the reversible Adiabatic process can be represented by �� = �� using P-V

& T-S diagrams.

6

Prove that the adiabatic index, � = ��

�� 6

What is an isothermal Process? Derive an equation for work done and change in I.E. for the

same.

6



Unit V Steam Properties Marks

Steam

Draw & explain the Phase Equilibrium diagram of water on

a) P-V & T-S diagrams

6

b) P-T & T-S diagrams 6

Explain the Phase Change process of a Pure Substance. 4

What is Critical Point? What are Critical Point parameters? Give values of Critical point

parameters for water. Explain the significance of Critical point.

6, 8

What do you mean by Triple point? Give triple point parameters of water. 4

Define:- Sensible heat, Latent Heat, Dryness fraction, Degree of Superheat, Pure Substance,

Critical Point, Triple point, Saturation Temperature

1/ 2

mark

each

Steam

processes

What is Quality of Steam? What are different methods of Measurement of Quality of Steam? 4

Explain the term “Dryness Fraction” in detail. 4

Define: Avogadro’s Number, Molar volume, Mole of a gas 4

Prove: For an Ideal Gas, Cp-Cv=R 4, 8

Draw p-V and T-s diagrams for isentropic and isochoric process of steam. 4

Calorimeters

Explain with a neat sketch- Throttling calorimeter, separating calorimeter, Combined Throttling

separating calorimeter, Barrel calorimeter

How quality of steam can be determined by using Throttling calorimeter/ separating

calorimeter/ Combined Throttling separating calorimeter/ Barrel calorimeter

Each

5/10

marks

Resources:

List of Useful Books

Essentials of Engineering Thermodynamics M M Rathore

Engineering Thermodynamics Joshi, Tumne, N K Patil

Engineering Thermodynamics P K Nag (TMH)

Thermodynamics: An Engineering Approach Cengel, Yunus A.;Boles

Useful websites

(If any link found broken/not working please inform [email protected])

www.thermofluids.net

(Best-animated site for understanding Thermodynamics and fluid mechanics)

www.nptel.iitm.ac.in

(For video/text for all 8 semesters of major branches of engineering)

www.youtube.com/nptel

(For NPTEL video lectures)

http://www.researchgate.net/

www.nasa.gov/centers/glenn/

nmu fe engg thermodynamics 2011

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