1. Applied Thermal Engineering
Syllabus Unit VI
Applied Thermal Engineering
Power Plant Engineering: Conventional and Non-conventional energy resources, Hydro-Electric, Thermal, Nuclear, Wind, Solar (with block diagram)
Power Producing Devices: Boiler – Water tube and fire tube, Internal Combustion Engines – Two stroke and four stroke (spark ignition and compression ignition), Turbines – Impulse & Reaction
Power Absorbing Devices: Pump – Reciprocating & Centrifugal, Compressors – Single acting, Single stage reciprocating air compressor, Refrigerator – Vapour compression refrigeration process, House hold refrigerator, Window air conditioner (working with block diagram)

2. Objective and Outcomes of Unit V
Understand the basic principles of thermodynamics along with first and second law
Outcomes of Unit V:
Able to understand first and second law of thermodynamics of thermodynamics along with application
Able to understand basic principle of simple pressure and temperature measuring devices

3. Internal Combustion(IC) Engines
Spark Ignition (SI) Engines
Or Petrol(Gasoline) Engine
Two Stroke
Four Stroke
Compression Ignition (CI) Engines
Or Diesel Engines

4. Working of Four Stroke Petrol Engine
Intake Stroke:
Piston moves from TDC to BDC creating vacuum in the cylinder
At the same time intake valve opens. Mixture of air and vaporized petrol enters from carburetor through intake manifold
TDC
BDC
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IV: Intake Valve
EV: Exhaust Valve
SP: Spark Plug
TDC: Top Dead Centre
BDC: Bottom Dead Centre
Top Dead Centre: Upper limit up to which piston surface can go
Bottom Dead Centre: Lower limit up to which piston surface can come down

5. Working of Four Stroke Petrol Engine
Compression Stroke:
Both valves stay closed
Piston moves from BDC to TDC, compressing air up to 8:1 compression ratio
TDC
BDC
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IV: Intake Valve
EV: Exhaust Valve
SP: Spark Plug
TDC: Top Dead Centre
BDC: Bottom Dead Centre

6. Working of Four Stroke Petrol Engine
Expansion/Power Stroke:
Both valves stay closed
When the piston is at the end of compression stroke(TDC) the spark plug delivers an electric spark which initiates combustion
The combustion inside the petrol engine is almost instantaneous and it will take place nearly at constant volume i.e. when the piston is at TDC
Expanding gases push the piston from TDC to BDC. Thus power is produced in expansion stroke
TDC
BDC
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IV: Intake Valve
EV: Exhaust Valve
SP: Spark Plug
TDC: Top Dead Centre
BDC: Bottom Dead Centr

7. Working of Four Stroke Petrol Engine
Exhaust Stroke:
Exhaust valve opens, intake valve remains closed
Piston moves from BDC to TDC
Exhaust gases escape through exhaust manifold
TDC
BDC
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IV: Intake Valve
EV: Exhaust Valve
SP: Spark Plug
TDC: Top Dead Centre
BDC: Bottom Dead Centre

8. Working of Four Stroke Diesel Engine
Fuel Injector
Intake Stroke:
Piston moves from TDC (Top Dead Centre) to BDC(Bottom Dead Centre) creating vacuum in the cylinder
At the same time intake valve opens allowing only air to enter the cylinder and exhaust valve remains closed
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9. Working of Four Stroke Diesel Engine
Fuel Injector
Compression Stroke:
Both valves stay closed
Piston moves from BDC to TDC, compressing air up to 22:1 compression ratio
Compressing the air to this extent increases the temperature inside the cylinder to around 7000C
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10. Working of Four Stroke Diesel Engine
Expansion/Power Stroke:
Both valves stay closed
When the piston is at the end of compression stroke(TDC) the fuel injector sprays a mist of diesel fuel into the cylinder.
Diesel will self ignite because very high temperature at end of compression stroke (around 7000C). The combustion inside the diesel engine is gradual and it will take place nearly at constant pressure
Expanding gases push the piston from TDC to BDC. Thus power is produced in expansion stroke
Fuel Injector
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11. Working of Four Stroke Diesel Engine
Exhaust Stroke:
Exhaust valve opens, intake valve remains closed
Piston moves from BDC to TDC
Exhaust gases escape through exhaust manifold
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12. Working of Two Stroke Petrol Engine
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13. Working of Two Stroke Petrol Engine
Crank case contains air at and fuel mixture at atmospheric pressure
As the piston approaches towards BDC air inside the crank case compresses and enters inside the cylinder via transfer port
The piston starts moving towards TDC
The piston surface closes exhaust as well as transfer port
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14. Working of Two Stroke Petrol Engine
As the piston approaches towards TDC air inside the cylinder gets compressed
At same time vacuum gets created inside the crankcase, hence mixture of air and petrol vapor enters inside crank case through intake port
As the transfer port is closed, the mixture remains inside the crank case
At the end of compression, the spark plug delivers an electric spark which initiates combustion
The combustion inside the petrol engine is almost instantaneous and it will take place nearly at constant volume
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15. Working of Two Stroke Petrol Engine
The expanding gases push piston towards BDC, thus power is produced. At the same time air-fuel mixture gets compressed inside crank case
The exhaust port opens first and the burnt gases escape through exhaust port
Immediately after exhaust, the fresh mixture enters inside cylinder via transfer port
The deflector deflects fresh mixture away from the exhaust port so that it doesn’t get carried away along exhaust with exhaust gases
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16. Single acting Single stage Reciprocating Compressor

17. Classification of Turbines
Steam Turbines
Impulse Turbines
Reaction Turbines
Hydraulic Turbines
Pelton Turbines
Kaplan Turbines
Francis Turbines
Gas Turbines
Open Cycle Gas Turbines
Closed Cycle Gas Turbines

18. Impulse and Reaction turbines: Principle
Impulse Turbine:
The driving force required for rotor is obtained by impact of high velocity fluid on rotor blade
Reaction Turbine:
The driving force required for rotor is obtained by accelerating fluid through narrowing passage between rotor blades

19. Typical Rotor Blade section of impulse Turbine
Fixed Blades
Moving Blades
Typical Rotor Blade section of impulse Turbine

20. Impulse Turbine
The pressure is completely converted into kinetic energy at first stage itself. The nozzle is used to increase velocity at the expense of pressure
A part of kinetic energy is converted into mechanical energy because of impact of high speed steam on rotor blades
Stator blades are used to guide steam coming out from rotor stage to next stage
Rest of kinetic energy is absorbed in successive stages
Magnitude of relative velocity remains constant within each stage. However absolute velocity decrease in each rotor stage as K.E. gets converted into mechanical work
Pressure constant through out all stages except nozzle

21. Reaction Turbine Note: Stator blades are not shown here Moving Blades
Typical Rotor Blade section of Reaction Turbine

22. Reaction Turbine
The driving force in case of reaction turbine consist of two parts
1. Force obtained by reaction of accelerating steam passing through narrow passage in between rotor blades
Force obtained by change in direction of steam when it passes through rotor blades
The first part makes major contribution hence it is called reaction turbine
In case of pure reaction turbine stator blades only serve as a guide to change the direction of steam but for all practical reaction turbines stator also accelerates the fluid. Hence there will be pressure drop in rotor as well as stator
Magnitude of relative velocity increases within each rotor stage but absolute velocity decreases because K.E. gets converted into mechanical work

23. Centrifugal Pump Diffuser Type Volute Type
Note: Mixed type centrifugal pump uses both involute casing as well as diffuser to convert velocity into pressure
Mixed Type
Impeller

24. Centrifugal Pump
The suction pressure is created at the entry of pump because of centrifugal effect. Hence down stream water is sucked continuously into the pump
The fluid coming out of impeller has very high velocity because of speed imparted by impeller
Involute casing and/or diffuser vanes are used to convert this high velocity into pressure
Both the involute casing as well as diffuser have gradually increasing cross section. As area increase, the velocity will reduce and pressure will increase as per Bernoulli’s equation

25. Refrigeration System Refrigeration Systems Gas Refrigeration Systems
Vapor Refrigeration Systems
Vapor Compression Systems
Vapor Absorption Systems

26. Refrigeration System: Principle
“The boiling point of any liquid decrease with pressure”
If pressure on any saturated liquid is reduced then the liquid starts evaporating.
The latent heat for vaporization is absorbed from adjacent liquid hence liquid gets cooled until its boiling point corresponding to the lowered pressure achieved
e.g. If pressure of R12 refrigerant liquid at 300C is reduced from 744kPa to 150kPa then its temperature is lowered up to -200C
Properties of R12 Refrigerant (CCl2F2)
Pressure (kPa)
Boiling Point (0C) 64
-40
100
-30
150
-20
219
-10
308
423 10
566 20
744 30
Note: Saturated liquid is a liquid which by addition of slight heat (or by slight reduction in pressure) starts boiling. e.g water at 1000C and 1 atmospheric pressure is a liquid

27. Vapor Compression Refrigeration System
Expansion valve reduces the pressure of the saturated liquid coming from condenser
The liquid starts evaporating because of reduction in pressure
The latent heat for vaporization is absorbed from the adjacent liquid. Hence liquid gets cooled. The cooling continues till saturation temperature (boiling point) corresponding to lower pressure is attained. Thus at the end of expansion valve mixture of vapor and liquid at lower temperature

28. Vapor Compression Refrigeration System
The cold mixture is circulated through the evaporator coils which pass over the objects to be cooled.
The mixture absorbs heat from the objects hence remaining liquid also gets evaporated. Thus at the end of evaporator complete vapor is obtained
The refrigerant needs to be recycled back to the higher pressure hence the compressor is used to increase the pressure.
Note: The higher pressure is selected in such a way that the boiling point corresponding to it is above atmospheric temperature and the lower pressure is selected in such a way that the boiling point corresponding to it is below the desired cooling temperature

29. Vapor Compression Refrigeration System
At the end of compressor vapor at high pressure and high temperature is obtained
The vapor is condensed through the condenser by using atmospheric air as a coolant. Thus at the end of condenser saturated liquid at high pressure is obtained. The liquid is again recycled through the expansion valve

30. Window Air Conditioner

31. Window Air Conditioner
The working principle of window air conditioner and refrigerator is same just construction is different
Condenser and evaporator are separated from each other by a partition so that hot and cold air don’t mix with each other
Function of each unit is exactly same and student can give same explanation as provided in case of refrigerator
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