This document discusses power and refrigeration cycles. It provides classifications of cycles based on whether they produce or absorb work, the working fluid used, and the type of heat supplied. The key components of cycles are identified as the heat source, heat sink, and working fluid. The Brayton cycle is described as a gas turbine cycle consisting of constant pressure heat addition and rejection processes separated by isentropic compression and expansion. Expressions for the efficiency of the Brayton cycle are provided. Internal combustion cycles like the Otto and Diesel cycles are discussed as idealized air-standard cycles with assumptions made about the working fluid. The four processes and efficiency equations for the Otto and Diesel cycles are summarized.
A lot's of animation have been included in it which make this ppt more attractive as well audience better understand and key point of a good presentation is that if we are able to explain them in simpler way more people will going to like it so hope this ppt will really be helpfull
This presentation covers about 'Heat Engine' precisely.Two Stroke Engine, Four Stroke Engine-Comparison, working Principle, Description of Engine Components, Cooling system, Lubricating system, Timing Diagram etc. It will be helpful for Mechanical Engineering students, so will for Electrical Engineering Students and obviously for those who want to learn about 'Engine' to meet personal thirst. Enjoy.
A lot's of animation have been included in it which make this ppt more attractive as well audience better understand and key point of a good presentation is that if we are able to explain them in simpler way more people will going to like it so hope this ppt will really be helpfull
This presentation covers about 'Heat Engine' precisely.Two Stroke Engine, Four Stroke Engine-Comparison, working Principle, Description of Engine Components, Cooling system, Lubricating system, Timing Diagram etc. It will be helpful for Mechanical Engineering students, so will for Electrical Engineering Students and obviously for those who want to learn about 'Engine' to meet personal thirst. Enjoy.
Introduction to the second law
Thermal energy reservoirs
Heat engines
Thermal efficiency
The 2nd law: Kelvin-Planck statement
Refrigerators and heat pumps
Coefficient of performance (COP)
The 2nd law: Clasius statement
Perpetual motion machines
Reversible and irreversible processes
Irreversibility's, Internal and externally reversible processes
The Carnot cycle
The reversed Carnot cycle
The Carnot principles
The thermodynamic temperature scale
The Carnot heat engine
The quality of energy
The Carnot refrigerator and heat pump
This ppt is more useful for Civil Engineering students.
I have prepared this ppt during my college days as a part of semester evaluation . Hope this will help to current civil students for their ppt presentations and in many more activities as a part of their semester assessments.
I have prepared this ppt as per the syllabus concerned in the particular topic of the subject, so one can directly use it just by editing their names.
fundamentals & basics of pneumatic systemNitin Chand
This presentation shows
1)The evolution of the industrial technology.
2)Types of media used in industrial processes.
3) Difference advantages between pneumatics , hydraulics & electrical as a media
4) Brief of basic principals of pneumatic system.
here i have cover below topics
1. introduction
2. Components In Gas Turbine
3. Gas Turbine Working
4. Air Standard Cycle
5. Brayton Cycle
6. Brayton Cycle history
7. Gas Turbine Plant (Open Cycle)
8. Gas Turbine Plant (Close Cycle)
9. Brayton Cycle On P-V & T-S Plane
10. Efficiency of Brayton Cycle
11. Isentropic Efficiency Of Compressor
12. Isentropic Efficiency Of Turbine
13. Work Ratio
14. Merits and Demerits
Introduction to the second law
Thermal energy reservoirs
Heat engines
Thermal efficiency
The 2nd law: Kelvin-Planck statement
Refrigerators and heat pumps
Coefficient of performance (COP)
The 2nd law: Clasius statement
Perpetual motion machines
Reversible and irreversible processes
Irreversibility's, Internal and externally reversible processes
The Carnot cycle
The reversed Carnot cycle
The Carnot principles
The thermodynamic temperature scale
The Carnot heat engine
The quality of energy
The Carnot refrigerator and heat pump
This ppt is more useful for Civil Engineering students.
I have prepared this ppt during my college days as a part of semester evaluation . Hope this will help to current civil students for their ppt presentations and in many more activities as a part of their semester assessments.
I have prepared this ppt as per the syllabus concerned in the particular topic of the subject, so one can directly use it just by editing their names.
fundamentals & basics of pneumatic systemNitin Chand
This presentation shows
1)The evolution of the industrial technology.
2)Types of media used in industrial processes.
3) Difference advantages between pneumatics , hydraulics & electrical as a media
4) Brief of basic principals of pneumatic system.
here i have cover below topics
1. introduction
2. Components In Gas Turbine
3. Gas Turbine Working
4. Air Standard Cycle
5. Brayton Cycle
6. Brayton Cycle history
7. Gas Turbine Plant (Open Cycle)
8. Gas Turbine Plant (Close Cycle)
9. Brayton Cycle On P-V & T-S Plane
10. Efficiency of Brayton Cycle
11. Isentropic Efficiency Of Compressor
12. Isentropic Efficiency Of Turbine
13. Work Ratio
14. Merits and Demerits
Course in Pune University Mechanical Engineering ppt based on Engineering Fundamentals
of the
Internal Combustion Engine
Willard W. Pulkrabek
University of Wisconsin-· .. Platteville
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FellowBuddy.com is an innovative platform that brings students together to share notes, exam papers, study guides, project reports and presentation for upcoming exams.
We connect Students who have an understanding of course material with Students who need help.
Benefits:-
# Students can catch up on notes they missed because of an absence.
# Underachievers can find peer developed notes that break down lecture and study material in a way that they can understand
# Students can earn better grades, save time and study effectively
Our Vision & Mission – Simplifying Students Life
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Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
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About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Thermodynamics chapter:7 Some Power and Refrigerator Cycle
1. [R Gnyawali / P Timilsina] Page 1
Chapter-7
Some Power and Refrigeration Cycles
1. Classification of Cycles
1. Based upon work producing or absorbing
a. Power Cycle: A cycle which continuously converts the heat into work is called power
cycle. This cycle is called work producing. Example: Heat Engine
b. Refrigeration Cycle: A cycle which continuously transfers heat from a lower temperature to
higher temperature region is called refrigeration cycle. This cycle is called work absorbing
because it needs work input. Example: Heat Pump, Refrigerator
2. Based upon working fluid
a. Gas Cycle: The cycle in which the phase of working fluid doesn’t change during entire
process is called gas cycle. Example: Diesel Cycle, Otto Cycle
b. Vapor Cycle: If the working fluid is alternatively vaporized and condensed, then the cycle
is called vapor cycle. Example: Rankine Cycle, Refrigeration Cycle.
3. Based upon heat supplied
a. Internal Combustion Cycle (burning of fossil fuel within engine itself).
b. External Combustion Cycle (burning of fossil fuels in a boiler).
2. Components of Power/Refrigeration Cycles
1. Source: It is a thermal reservoir which is at high temperature and can supply heat energy to the
system. Example: Furnace, Combustion Chamber.
2. Sink: It is a thermal reservoir which is at low temperature and can absorb heat energy rejected by
the system. Example: Atmospheric Air, Ocean.
3. Working Fluid: The fluid within the system which absorbs heat and rejects heat while undergoing
a cycle is called working fluid. Example: Air, Water, Ammonia.
3. External Heat Transfer Cycles
3.1 Brayton Cycle
The Brayton Cycle, also called the Joule Cycle, was developed originally for use in a piston engine with
fuel injection. This cycle is the ideal cycle for the simple gas turbine. The air standard Brayton cycle is
composed of constant pressure heat transfer processes separated by isentropic expansion and compression
processes.
The closed-cycle Brayton engine is shown in figure below. The working fluid air enters the compressor in
state 1, where it is compressed isentropically until state 2 is reached and enters high temperature heat
exchanger. In this heat exchanger heat will be added to the fluid at constant pressure until state 3 is
reached. Now high temperature air enters the turbine, where an isentropic expansion occurs, producing
mechanical work. The working fluid (air) leaves the turbine at state 4 and enters low temperature heat
exchanger, where heat will be rejected from the fluid until state 1 is reached. After completing a cycle
previous processes will be repeated in same order.
Compression in compressor and expansion in turbine are assumed to be isentropic processes in the ideal
closed cycle air standard Brayton cycle. It is easier to construct compressor and turbine which operates
nearly adiabatic. However, it is difficult to approach reversibility.
2. [R Gnyawali / P Timilsina] Page 2
Closed Brayton Cycle Open Brayton Cycle
The efficiency of Brayton cycle is given by,
)(
)(
1
1
23
14
TTmC
TTmC
Q
Q
P
P
H
L
B
−
−
−=
−=η
)1(
)1(
1
2
3
2
1
4
1
−
−
−=
T
T
T
T
T
T
Bη
Here, process 2-3 and 4-1 are constant pressure process so P2 = P3 and P1 = P4
For isentropic process 1-2,
γ
γ 1
1
2
1
2
−
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
P
P
T
T
For isentropic process 3-4,
1
2
1
1
2
1
4
3
4
3
T
T
P
P
P
P
T
T
=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
−−
γ
γ
γ
γ
So,
2
3
1
4
T
T
T
T
=
………….eq(1)
Now, using eq(1) above efficiency equation becomes as;
3. [R Gnyawali / P Timilsina] Page 3
( ) γ
γ
γ
γ
η
1
1
1
2
3
4
2
1
1
1
1
111
−
−
−=
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−=−=−=
p
B
r
P
P
T
T
T
T
Where,
4
3
1
2
P
P
P
P
rp == is the pressure ratio.
* The efficiency of Brayton cycle depends upon the isentropic pressure ratio.
4. Internal Combustion Cycles
In many power producing devices, such as the automotive gasoline engine, the diesel engine, and the gas
turbine, the working fluid is a gas. Broadly speaking, these devices take in either mixture of fuel and air or
fuel and air separately, compress this charge to a high pressure and cause the fuel to burn. A part of the
energy liberated as heat as a result of combustion is converted into useful work by causing the high
pressure and temperature products of combustion to expand in the engine or turbine while the remainder is
carried away with the exhaust gas living the device.
In general, the properties of the fuel air mixture before combustion approximates closely to those of air.
The properties of the products of combustion also do not differ much from those of pure air. For this
reason, it is convenient to analyze the performance of these devices by devising the idealized cycles
known as air standard cycles.
The air-standard cycles are based on the following hypothetical assumptions:
1. The working substance consists of a fixed mass of air. This closed system undergoes a cycle of
processes so that the system is restored to its initial state at the end of each cycle.
2. The combustion process is replaced by an equivalent heat addition process from an external
source. Thus there is no change in the chemical composition of the working fluid.
3. The exhaust process is replaced by an equivalent heat rejection process.
4. [R Gnyawali / P Timilsina] Page 4
4. Compression and expansion processes in the cycle are reversible adiabatic processes.
5. The specific heats CP and CV of air do not vary with temperature.
4.1 Air-standard Otto Cycle
The Otto Cycle is an ideal cycle for SI (Spark Ignition) engines. In most SI engines (Petrol engine) the
piston executes the four complete strokes within the cylinder and completes a thermodynamic cycle. The
working fluid for an Otto cycle is air. Before the combustion, the working fluid is mixture of fuel and air
and after the combustion the working fluid is combustion gases. However, for approximation, property of
air is considered. An Otto cycle is completed by four processes.
Process 1-2: Isentropic Compression: Fuel-air mixture is taken into the cylinder through suction
and the mixture inside the cylinder is compressed until the piston reaches the Top Dead Center (TDC).
This process is reversible and adiabatic. The pressure and temperature of the air increase.
Process 2-3: Constant Volume Heat Addition: The compressed air-fuel mixture is burned with a
spark which makes the pressure and temperature of the combustion gases to rise. This process is assumed
to occur at constant volume.
Process 3-4: Isentropic Expansion: The piston begins to move until it reaches Bottom Dead Center
(BDC) so the expansion of gas occurs adiabatically and reversibly. This process generates work output
and the pressure and temperature of air decreases consequently.
Process 4-1: Constant Volume Heat Rejection: The exhaust valve opens and the pressure and
temperature of gas decreases at constant volume. Then the gas is removed from the cylinder by movement
of piston and the cycle is completed.
The thermal efficiency of this cycle is given as:
H
L
H
LH
Q
Q
Q
QQ
−=
−
=
1
η
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−
−=
−
−
−=
1
1
1
)(
)(
1
2
3
2
1
4
1
23
14
T
T
T
T
T
T
TTmC
TTmC
V
V
5. [R Gnyawali / P Timilsina] Page 5
Since process 1-2 and 3-4 are isentropic, we can write,
( ) 1
1
2
1
1
2 −
−
=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
γ
γ
cr
V
V
T
T
Where, ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
2
1
V
V
rc is called compression ratio
And,
1
2
1
2
1
1
3
4
4
3
T
T
V
V
V
V
T
T
=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
−− γγ
So,
( ) 1
2
1 1
11 −
−=−= γ
η
crT
T
This shows that the efficiency of the otto cycle depends on the compression ratio. Efficiency of the otto
cycle increases with increase in compression ratio.
Mean Effective Pressure (MEP) is defined as the pressure that, if it acted on the piston during the entire
power stroke, would do an amount of work equal to that actually done on the piston.
21minmax vv
q
VV
W
eSweptvolum
Workdone
MEP HNET
−
=
−
==
η
1
2
3
4
Suction Exhaust
P
V
QH
QL
W
1
2
3
4
T
S
Q
H
QL
W
TDC BDC
Stroke
6. [R Gnyawali / P Timilsina] Page 6
4.2 Air-Standard Diesel Cycle
The diesel cycle is the ideal cycle for Compression Ignition (CI) engines. In diesel cycle, air is compressed
to a higher temperature which ignites the fuel. The diesel cycle differs from Otto Cycle, in that heat is
supplied at constant pressure instead of at constant volume. The working fluid for a Diesel cycle is air.
Before the combustion, the working fluid is atmospheric air and after the combustion the working fluid is
combustion gases. However, for approximation, properties of air are considered. A diesel cycle is
completed by four processes.
Process 1-2: Isentropic Compression: Air is taken into the cylinder through suction and air inside
the cylinder is compressed until the piston reaches the Top Dead Center (TDC). This process is reversible
and adiabatic. The pressure and temperature of the air increase.
Process 2-3: Constant Pressure Heat Addition: Fuel is injected in the cylinder so that compressed
air and fuel is burned spontaneously which makes the pressure and temperature of the combustion gases to
rise. Simultaneously, the piston moves maintaining the pressure inside the cylinder. This process is
assumed to occur at constant pressure.
Process 3-4: Isentropic Expansion: The piston begins to move until it reaches Bottom Dead Center
(BDC) so the expansion of gas occurs adiabatically and reversibly. This process generates work output
and the pressure and temperature of air decreases consequently.
Process 4-1: Constant Volume Heat Rejection: The exhaust valve opens and the pressure and
temperature of gas decreases at constant volume. Then the gas is removed from the cylinder by movement
of piston and the cycle is completed.
The thermal efficiency of diesel cycle is given by,
QL
8. [R Gnyawali / P Timilsina] Page 8
( )
⎥
⎥
⎥
⎥
⎥
⎦
⎤
⎢
⎢
⎢
⎢
⎢
⎣
⎡
−
−⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−=
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−
−=
−
−
1
1
1
1
1
1
1
2
3
1
2
3
1
2
3
2
1
4
1
T
T
T
T
r
T
T
T
T
T
T
c
γ
γ
ρ
γ
γ
η
For constant pressure process 2-3, ρ==
2
3
2
3
V
V
T
T
So,
( )
( ) ⎥
⎦
⎤
⎢
⎣
⎡
−
−
−=
⎥
⎦
⎤
⎢
⎣
⎡
−
−
−=
−
−
−
1
11
1
1
11
1
1
1
1
ρ
ρ
γ
ρ
ρρ
γ
η
γ
γ
γ
γ
c
c
r
r
The compression ratio of the diesel cycle is always greater than the expansion ratio. So for a given
compression ratio rC, the diesel engine always has lower efficiency than an Otto engine operating at the
same compression ratio.
5. Rankine Cycle
Rankine Cycle is the theoretical cycle on which steam power plants work. In Rankine cycle has water as
working fluid which is used to handle the phase change between liquid and vapor. The processes involved in
a Rankine cycle are:
Process 1-2: Reversible adiabatic compression in pump
Process 2-3: Constant pressure transfer of heat in the boiler
Process 3-4: Reversible adiabatic expansion in the turbine
Process 4-1: Constant pressure transfer of heat in the condenser
In an ideal Rankine Cycle as shown in figure below, the process 1-2, a pump is used to increase the
pressure of the working fluid. The working fluid enters the pump as a saturated liquid (State 1, x1 = 0) and
exits the pump as a sub-cooled liquid (state 2). The fluid entered into boiler has relatively low temperature
is heated at constant pressure and leaves the boiler as a saturated vapor (state 3, x3 = 1). This saturated
vapor is expanded isentropically through turbine to produce the work and leave as state 4. The low
pressure saturated mixture is again condensed at constant pressure in the condenser leaving as low
pressure low temperature saturated liquid (state 1). Following condensation, the liquid enters the pump.
The working fluid is returned to the high pressure for heat addition at the higher boiler temperature, and
the cycle is repeated.
For Boiler: Heat addition qin = h3 – h2
For Pump: Work Absorbed WP = h2 – h1
9. [R Gnyawali / P Timilsina] Page 9
For Turbine: work produced WT = h3 – h4
For Condenser: Heat loss qout = h4 – h1
So, efficiency of Rankine Cycle is:
)(
)()(
23
1243
hh
hhhh
−
−−−
=η
As compared to WT, WP is very small so in many cases we can write,
)(
)(
23
43
hh
hh
−
−
=η
10. [R Gnyawali / P Timilsina] Page 10
Effect of Pressure and Temperature on Rankine Cycle
1. Decreasing Condenser Pressure:
Let the exhaust pressure drop from P4 to P4’, with the corresponding decrease in temperature at which the
heat is rejected. The heat transfer to the steam is increased and the net work is also increased. The net
result is an increase in efficiency.
2. Increasing Boiler Pressure:
By increasing boiler pressure, the heat rejected decreases by keeping the maximum temperature constant.
The net work tends to remain same. Hence the efficiency increases.
3. Superheating Steam in Boiler:
The work increases and the heat transfer in boiler also increase. Since the ratio
HQ
W
′
′
is greater than
HQ
W
,
the efficiency of the cycle increases.
6. Vapor Compression Refrigeration Cycle
The most common method of providing air-conditioning and chilling as well as heat pumping is the vapor
compression cycle. In this cycle, the working substance changes phase during the cycle, in a manner
equivalent to that of Rankine cycle. The basic operation involved in vapor compression refrigeration cycle
is shown in figure below. It consists of four processes.
11. [R Gnyawali / P Timilsina] Page 11
1. Compression: At state 1, the fluid is a saturated or superheated vapor. This fluid is compressed
reversibly and adiabatically in process 1-2 by the compressor. As a result, the pressure and
temperature of vapor increases.
2. Condensation: The vapor is then condensed in process 2-3 through the condenser. In this process,
the vapor rejects heat to the surroundings at constant pressure and is converted into saturated
liquid.
3. Expansion: The saturated liquid is allowed to expand adiabatically in the throttling valve in
process 3-4. In this process, the pressure and temperature of the fluid decreases but enthalpy
remains constant. At state 4, the fluid is in two-phase mixture.
4. Evaporation: The two-phase mixture, then, absorbs heat from the surroundings and is converted
to saturated vapor in the evaporator. This process 4-1 occurs at constant pressure. This saturated
vapor is passed to compressor and the cycle completes.
The performance of a refrigeration system is defined as
12
41
hh
hh
W
Q
COP
in
L
R
−
−
==
Similarly, for the heat pump
12
32
hh
hh
W
Q
COP
in
H
HP
−
−
==