This document provides an overview of refrigeration and its history. It discusses how refrigeration works using the reverse Carnot cycle and various components like the evaporator, compressor, condenser and expansion valve. It then reviews the early history of refrigeration including using ice for food preservation, early experimental refrigeration systems in the 18th century, and the development of vapor compression and gas absorption cycles in the 19th century. The document also discusses the commercialization and widespread use of refrigeration in industries like breweries in the late 19th century and the development of home refrigerators in the early 20th century using synthetic refrigerants.
Removing undesirable heat from one item, substance, or area and transferring it to another is known as refrigeration, sometimes known as chilling. The temperature can be lowered by removing heat, which can be done using ice, snow, cooled water, or mechanical refrigeration.
The document discusses refrigeration and refrigeration cycles. It provides details on:
1) The basic components and process of a refrigerator, which uses ammonia as a refrigerant to draw heat from the freezer and fridge compartments via a compression and evaporation cycle.
2) Refrigeration cycles in general work by using a refrigerant to move heat from one place to another through evaporation and condensation.
3) The vapor compression refrigeration cycle involves compressing, condensing, expanding, and evaporating stages to transfer heat from the evaporator to the condenser.
This document provides an overview of refrigerators and freezers. It discusses the history of refrigeration from early icehouses to modern home appliances. Key developments include William Cullen demonstrating artificial refrigeration in 1748, Oliver Evans inventing the vapor-compression refrigeration machine in 1805, and Carl von Linde developing important refrigeration technologies in the late 19th century. The document also describes the introduction of home refrigerators in the 1920s and their widespread adoption after World War II with new features like automatic defrosting. Freezers became common household appliances starting in the 1940s.
This document discusses the history of refrigerant and compressor development. It describes the early use of natural refrigerants like water and how synthetic refrigerants like Freon were developed in the 1920s. It also discusses the key issues with early refrigerants like toxicity and flammability that synthetic refrigerants solved. However, synthetic refrigerants like CFCs were later found to deplete the ozone layer, prompting a search for new non-ozone depleting refrigerants. The document provides a high-level overview of the major developments and issues in both refrigerants and compressor technology over time.
This document discusses refrigeration and air conditioning. It begins by describing the early history of ice harvesting and refrigeration before mechanical refrigeration. It then defines refrigeration as the process of moving heat from one location to another, often using mechanical work. Refrigeration systems are classified as vapor compression or vapor absorption. Vapor compression refrigeration uses compressed fluids that expand and get colder, removing heat from one space and transferring it to another. Refrigeration has significantly impacted industry, lifestyle, agriculture, and development by allowing food preservation and temperature control.
This document provides a sector analysis of cold chain logistics. It begins with definitions of logistics and cold chain logistics. There is then a history of breakthroughs in refrigerated transportation from the 18th century to recent developments. Sections also discuss the global scenario for cold chain in food and pharmaceuticals, including temperature standards and product shelf lives. The document outlines the major players in the global cold chain industry and discusses important value parameters for cold chain logistics users.
Removing undesirable heat from one item, substance, or area and transferring it to another is known as refrigeration, sometimes known as chilling. The temperature can be lowered by removing heat, which can be done using ice, snow, cooled water, or mechanical refrigeration.
The document discusses refrigeration and refrigeration cycles. It provides details on:
1) The basic components and process of a refrigerator, which uses ammonia as a refrigerant to draw heat from the freezer and fridge compartments via a compression and evaporation cycle.
2) Refrigeration cycles in general work by using a refrigerant to move heat from one place to another through evaporation and condensation.
3) The vapor compression refrigeration cycle involves compressing, condensing, expanding, and evaporating stages to transfer heat from the evaporator to the condenser.
This document provides an overview of refrigerators and freezers. It discusses the history of refrigeration from early icehouses to modern home appliances. Key developments include William Cullen demonstrating artificial refrigeration in 1748, Oliver Evans inventing the vapor-compression refrigeration machine in 1805, and Carl von Linde developing important refrigeration technologies in the late 19th century. The document also describes the introduction of home refrigerators in the 1920s and their widespread adoption after World War II with new features like automatic defrosting. Freezers became common household appliances starting in the 1940s.
This document discusses the history of refrigerant and compressor development. It describes the early use of natural refrigerants like water and how synthetic refrigerants like Freon were developed in the 1920s. It also discusses the key issues with early refrigerants like toxicity and flammability that synthetic refrigerants solved. However, synthetic refrigerants like CFCs were later found to deplete the ozone layer, prompting a search for new non-ozone depleting refrigerants. The document provides a high-level overview of the major developments and issues in both refrigerants and compressor technology over time.
This document discusses refrigeration and air conditioning. It begins by describing the early history of ice harvesting and refrigeration before mechanical refrigeration. It then defines refrigeration as the process of moving heat from one location to another, often using mechanical work. Refrigeration systems are classified as vapor compression or vapor absorption. Vapor compression refrigeration uses compressed fluids that expand and get colder, removing heat from one space and transferring it to another. Refrigeration has significantly impacted industry, lifestyle, agriculture, and development by allowing food preservation and temperature control.
This document provides a sector analysis of cold chain logistics. It begins with definitions of logistics and cold chain logistics. There is then a history of breakthroughs in refrigerated transportation from the 18th century to recent developments. Sections also discuss the global scenario for cold chain in food and pharmaceuticals, including temperature standards and product shelf lives. The document outlines the major players in the global cold chain industry and discusses important value parameters for cold chain logistics users.
This document provides an overview of refrigeration and air conditioning fundamentals and components. It begins with a history of refrigeration from ancient times to modern developments. It then describes the six main classifications within the industry: appliance servicing, commercial refrigeration, industrial refrigeration, transport and marine, comfort air conditioning, and process air conditioning. The document outlines key temperatures used for food storage and human comfort. It also includes content on refrigeration fundamentals, major system components, air conditioning basics, and an assessment section.
Cryogenics is the study of production and behavior of materials at very low temperatures, typically below -150°C. It involves using cryogenic liquids like liquid nitrogen and liquid helium to reach these low temperatures. Some key applications of cryogenics include magnetic resonance imaging (MRI), which uses superconducting magnets cooled by liquid helium; cryogenic rocket engines, which use cryogenically stored liquid oxygen and hydrogen as fuel; and cryogenic processing of metals to improve properties like wear resistance. Cryogenics also enables applications in fields like space technology, electronics, medicine, and more.
Cryogenics is the production and behavior of materials at very low temperatures, below 120K. There are four main methods for producing cryogenic temperatures: heat conduction, evaporative cooling, the Joule-Thomson effect, and adiabatic demagnetization. Cryogenics has many applications, including in rocket fuel as cryogenic liquids like liquid hydrogen provide high energy per unit mass. Other applications include cryosurgery, frozen food storage, and specialty effects using liquid nitrogen fog. Issues include the dangerous nature of handling cryogenic gases and liquids as well as storage challenges posed by low temperatures and high pressures.
This document provides an overview of the history of refrigeration. It discusses natural refrigeration methods such as use of ice, evaporative cooling, and cooling with salt solutions. It then discusses the development of artificial refrigeration, including William Cullen's demonstration of refrigeration using ether in 1755. Key developments discussed include Jacob Perkins' vapor compression refrigeration system in 1834 using ether, the use of ammonia as a refrigerant starting in the 1870s, and the development of domestic refrigeration systems starting in the early 1900s using various refrigerants before settling on Freon-12 in the 1930s. The document aims to define refrigeration and air conditioning and discuss natural and artificial refrigeration methods and their history.
This document summarizes a study that investigated using a propane-butane mixture as an alternative refrigerant in household refrigerators instead of R-134a. The study found that using a mixed refrigerant of 80% propane and 20% butane by mass achieved higher cooling capacity and lower freezer temperatures compared to R-134a, with energy consumption reduced by nearly 10.8%. Mixed refrigerants are a potential environmentally-friendly alternative to hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) that are banned for depleting the ozone layer. The experimental results indicate that mixed refrigerants show promise as refrigerants in household refrigerators.
The early history of refrigerators involved digging holes in the ground or building structures to store ice cut from frozen ponds in order to preserve food. The first modern refrigerator was designed in 1748, but it wasn't until the late 19th and early 20th centuries that fridges for home use were invented. In the 1920s, self-contained refrigerators and Freon became widespread, expanding the market. Technical advances in the mid-20th century included automatic defrosting and ice making.
Introduction to cryogenics engineering from CERNmarcoandresauza
This document provides an overview of an introductory course on cryogenic engineering. The course covers topics like the history of cryogenics from early refrigeration methods to modern cycles, standard components, heat transfer and insulation, safety, and applications. The first day focuses on the history from Newton's time to modern refrigeration cycles like the Linde-Hampson cycle. It discusses key historical figures and developments. Standard components covered on the second day include refrigerants, cryostats, and material properties. The course examines refrigeration principles, cycles, and expansion machines.
This document provides an introduction to adsorption refrigeration techniques. It discusses how adsorption refrigeration can provide an alternative refrigeration solution in developing areas without reliable electricity. The document then summarizes the history and development of adsorption refrigeration, environmental regulations driving its development, advantages over absorption refrigeration, key terms related to adsorption refrigeration systems, and the objectives and aims of studying adsorption refrigeration as an alternative refrigeration approach.
This slide is about some new green cooling system (refrigeration system) and green refrigerant. For the Ozone layer depletion and green house effect, it is high time to find new refrigerant and refrigeration system.
Refrigeration is defined as reducing and maintaining the temperature of materials below the surrounding temperature. There are several types of refrigeration including non-cyclic, cyclic, thermoelectric, and magnetic. Cyclic refrigeration includes vapor compression and vapor absorption refrigeration cycles which use a refrigerant and involve compression, condensation, expansion, and evaporation/cooling. Refrigeration has many commercial and industrial uses such as food transportation and storage.
Chilling Tales: The Fascinating History Of Air ConditioningEZAirconServicing
With summer just around the corner, the demand for air conditions and aircon servicing to make our lives more comfortable in the sweltering heat of Singapore is high. Visit https://ezaircon.sg/ to learn more.
This document describes the design of an ice manufacturing plant with a production capacity of 2000 pounds per day. It discusses the main components of the refrigeration system, including the condenser, compressor, evaporator and expansion device. The design calculations determine the required cooling capacity, compressor size, evaporator tube length, and condenser tube length. These include determining the heat rejected from water, refrigerant flow rate, piston displacement, heat transfer coefficients, and surface areas. The goal is to reduce the water temperature from 27°C to -7.2°C. The design considers factors like refrigerant type, operating temperatures, compressor speed, and heat exchange calculations.
A drying process in which moisture is first converted to ice and then through reduced pressure and increase temperature it is directly converted to water vapor ( sublimation).
Complete process description, process parameters , types of freeze drying, case study of effect of different drying process on apple peels
Air conditioning Theory Lecture 1 Kaleem-1.pptxBawaseerKhan
This document discusses air conditioning and refrigeration. It covers the definitions and differences between refrigeration and air conditioning. Refrigeration is the process of achieving and maintaining a temperature lower than the surroundings, while air conditioning simultaneously controls temperature, moisture, and air quality for human comfort or process needs. The document outlines the history of refrigeration from natural to artificial methods like vapor compression cycles. It also covers applications of refrigeration and air conditioning in areas like food processing, chemical industries, and industrial/comfort air conditioning.
The document discusses the history and evolution of refrigerators. It notes that ancient cultures used ice to preserve food, and that refrigerators are now common worldwide. It describes typical refrigerator sizes and a Mexican government program to replace old refrigerators. The document then discusses the early history of refrigeration technology from ancient China to the first domestic refrigerators in the 19th century powered by gas and electricity. It notes important innovations like Freon in 1930 and chlorofluorocarbons in 1931 that improved safety. Regular defrosting and cleaning of refrigerators is also recommended.
1. Solar refrigeration has applications in both developing and developed countries for vaccine storage, food preservation, and air conditioning. Previous research on photovoltaic and solar thermal refrigeration systems is reviewed.
2. Research is underway at Warwick University on carbon-ammonia refrigerators driven by steam heat from a thermosyphon heat pipe sourced by solar energy or biomass. A new area of interest is using desiccant wheel technology for solar powered air conditioning.
3. The basic principles of solar absorption refrigeration are described and past experience is assessed. Solar absorption refrigeration shows potential but current systems are still costly.
The origins of air conditioning are unclear, though early experiments included blowing air over ice-cooled rooms. In the 1830s, Dr. John Gorrie built a device to cool rooms and treat fever patients. In 1902, Willis Carrier developed the first modern air conditioning system to control temperature and humidity in factories. Early models had problems but improved in 1922 when a safer coolant replaced ammonia. By the 1930s, air conditioning was common in public spaces, and window units drove widespread home use in the 1950s. Today, most Americans consider home air conditioning a necessity.
Refrigeration is a process that removes heat from an enclosed space to lower its temperature below the surrounding temperature. Zeolites are microporous minerals commonly used as commercial adsorbents. They have a crystalline structure made up of silicon, aluminum and oxygen tetrahedra that form pores and cavities. Zeolites can adsorb large amounts of water due to their porous structure and electrostatic fields. Their ability to adsorb water makes them promising candidates for solar refrigeration applications by utilizing the zeolite-water adsorption process.
The document discusses offensive speech and the FBI's priority to protect citizens from hate crimes and terrorism. While the First Amendment protects free speech, the government's view of offensive speech has evolved over time. Courts play a key role in protecting free speech from government overregulation based on interpreting the First Amendment.
How To Write An Opinion Essay Essay TigersMonica Waters
This document discusses HR recruitment practices for hiring employees. It explains that HR recruitment was originally used primarily by large corporations but is now common for many ordinary companies as well. The needs of HR recruitment in organizations have changed in recent years, and the process now exists in most organizations to improve efficiency. The recruitment system is at the heart of every business, so ensuring consistency at every level is important to enhance effectiveness in hiring and retention.
This document provides an overview of refrigeration and air conditioning fundamentals and components. It begins with a history of refrigeration from ancient times to modern developments. It then describes the six main classifications within the industry: appliance servicing, commercial refrigeration, industrial refrigeration, transport and marine, comfort air conditioning, and process air conditioning. The document outlines key temperatures used for food storage and human comfort. It also includes content on refrigeration fundamentals, major system components, air conditioning basics, and an assessment section.
Cryogenics is the study of production and behavior of materials at very low temperatures, typically below -150°C. It involves using cryogenic liquids like liquid nitrogen and liquid helium to reach these low temperatures. Some key applications of cryogenics include magnetic resonance imaging (MRI), which uses superconducting magnets cooled by liquid helium; cryogenic rocket engines, which use cryogenically stored liquid oxygen and hydrogen as fuel; and cryogenic processing of metals to improve properties like wear resistance. Cryogenics also enables applications in fields like space technology, electronics, medicine, and more.
Cryogenics is the production and behavior of materials at very low temperatures, below 120K. There are four main methods for producing cryogenic temperatures: heat conduction, evaporative cooling, the Joule-Thomson effect, and adiabatic demagnetization. Cryogenics has many applications, including in rocket fuel as cryogenic liquids like liquid hydrogen provide high energy per unit mass. Other applications include cryosurgery, frozen food storage, and specialty effects using liquid nitrogen fog. Issues include the dangerous nature of handling cryogenic gases and liquids as well as storage challenges posed by low temperatures and high pressures.
This document provides an overview of the history of refrigeration. It discusses natural refrigeration methods such as use of ice, evaporative cooling, and cooling with salt solutions. It then discusses the development of artificial refrigeration, including William Cullen's demonstration of refrigeration using ether in 1755. Key developments discussed include Jacob Perkins' vapor compression refrigeration system in 1834 using ether, the use of ammonia as a refrigerant starting in the 1870s, and the development of domestic refrigeration systems starting in the early 1900s using various refrigerants before settling on Freon-12 in the 1930s. The document aims to define refrigeration and air conditioning and discuss natural and artificial refrigeration methods and their history.
This document summarizes a study that investigated using a propane-butane mixture as an alternative refrigerant in household refrigerators instead of R-134a. The study found that using a mixed refrigerant of 80% propane and 20% butane by mass achieved higher cooling capacity and lower freezer temperatures compared to R-134a, with energy consumption reduced by nearly 10.8%. Mixed refrigerants are a potential environmentally-friendly alternative to hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) that are banned for depleting the ozone layer. The experimental results indicate that mixed refrigerants show promise as refrigerants in household refrigerators.
The early history of refrigerators involved digging holes in the ground or building structures to store ice cut from frozen ponds in order to preserve food. The first modern refrigerator was designed in 1748, but it wasn't until the late 19th and early 20th centuries that fridges for home use were invented. In the 1920s, self-contained refrigerators and Freon became widespread, expanding the market. Technical advances in the mid-20th century included automatic defrosting and ice making.
Introduction to cryogenics engineering from CERNmarcoandresauza
This document provides an overview of an introductory course on cryogenic engineering. The course covers topics like the history of cryogenics from early refrigeration methods to modern cycles, standard components, heat transfer and insulation, safety, and applications. The first day focuses on the history from Newton's time to modern refrigeration cycles like the Linde-Hampson cycle. It discusses key historical figures and developments. Standard components covered on the second day include refrigerants, cryostats, and material properties. The course examines refrigeration principles, cycles, and expansion machines.
This document provides an introduction to adsorption refrigeration techniques. It discusses how adsorption refrigeration can provide an alternative refrigeration solution in developing areas without reliable electricity. The document then summarizes the history and development of adsorption refrigeration, environmental regulations driving its development, advantages over absorption refrigeration, key terms related to adsorption refrigeration systems, and the objectives and aims of studying adsorption refrigeration as an alternative refrigeration approach.
This slide is about some new green cooling system (refrigeration system) and green refrigerant. For the Ozone layer depletion and green house effect, it is high time to find new refrigerant and refrigeration system.
Refrigeration is defined as reducing and maintaining the temperature of materials below the surrounding temperature. There are several types of refrigeration including non-cyclic, cyclic, thermoelectric, and magnetic. Cyclic refrigeration includes vapor compression and vapor absorption refrigeration cycles which use a refrigerant and involve compression, condensation, expansion, and evaporation/cooling. Refrigeration has many commercial and industrial uses such as food transportation and storage.
Chilling Tales: The Fascinating History Of Air ConditioningEZAirconServicing
With summer just around the corner, the demand for air conditions and aircon servicing to make our lives more comfortable in the sweltering heat of Singapore is high. Visit https://ezaircon.sg/ to learn more.
This document describes the design of an ice manufacturing plant with a production capacity of 2000 pounds per day. It discusses the main components of the refrigeration system, including the condenser, compressor, evaporator and expansion device. The design calculations determine the required cooling capacity, compressor size, evaporator tube length, and condenser tube length. These include determining the heat rejected from water, refrigerant flow rate, piston displacement, heat transfer coefficients, and surface areas. The goal is to reduce the water temperature from 27°C to -7.2°C. The design considers factors like refrigerant type, operating temperatures, compressor speed, and heat exchange calculations.
A drying process in which moisture is first converted to ice and then through reduced pressure and increase temperature it is directly converted to water vapor ( sublimation).
Complete process description, process parameters , types of freeze drying, case study of effect of different drying process on apple peels
Air conditioning Theory Lecture 1 Kaleem-1.pptxBawaseerKhan
This document discusses air conditioning and refrigeration. It covers the definitions and differences between refrigeration and air conditioning. Refrigeration is the process of achieving and maintaining a temperature lower than the surroundings, while air conditioning simultaneously controls temperature, moisture, and air quality for human comfort or process needs. The document outlines the history of refrigeration from natural to artificial methods like vapor compression cycles. It also covers applications of refrigeration and air conditioning in areas like food processing, chemical industries, and industrial/comfort air conditioning.
The document discusses the history and evolution of refrigerators. It notes that ancient cultures used ice to preserve food, and that refrigerators are now common worldwide. It describes typical refrigerator sizes and a Mexican government program to replace old refrigerators. The document then discusses the early history of refrigeration technology from ancient China to the first domestic refrigerators in the 19th century powered by gas and electricity. It notes important innovations like Freon in 1930 and chlorofluorocarbons in 1931 that improved safety. Regular defrosting and cleaning of refrigerators is also recommended.
1. Solar refrigeration has applications in both developing and developed countries for vaccine storage, food preservation, and air conditioning. Previous research on photovoltaic and solar thermal refrigeration systems is reviewed.
2. Research is underway at Warwick University on carbon-ammonia refrigerators driven by steam heat from a thermosyphon heat pipe sourced by solar energy or biomass. A new area of interest is using desiccant wheel technology for solar powered air conditioning.
3. The basic principles of solar absorption refrigeration are described and past experience is assessed. Solar absorption refrigeration shows potential but current systems are still costly.
The origins of air conditioning are unclear, though early experiments included blowing air over ice-cooled rooms. In the 1830s, Dr. John Gorrie built a device to cool rooms and treat fever patients. In 1902, Willis Carrier developed the first modern air conditioning system to control temperature and humidity in factories. Early models had problems but improved in 1922 when a safer coolant replaced ammonia. By the 1930s, air conditioning was common in public spaces, and window units drove widespread home use in the 1950s. Today, most Americans consider home air conditioning a necessity.
Refrigeration is a process that removes heat from an enclosed space to lower its temperature below the surrounding temperature. Zeolites are microporous minerals commonly used as commercial adsorbents. They have a crystalline structure made up of silicon, aluminum and oxygen tetrahedra that form pores and cavities. Zeolites can adsorb large amounts of water due to their porous structure and electrostatic fields. Their ability to adsorb water makes them promising candidates for solar refrigeration applications by utilizing the zeolite-water adsorption process.
The document discusses offensive speech and the FBI's priority to protect citizens from hate crimes and terrorism. While the First Amendment protects free speech, the government's view of offensive speech has evolved over time. Courts play a key role in protecting free speech from government overregulation based on interpreting the First Amendment.
How To Write An Opinion Essay Essay TigersMonica Waters
This document discusses HR recruitment practices for hiring employees. It explains that HR recruitment was originally used primarily by large corporations but is now common for many ordinary companies as well. The needs of HR recruitment in organizations have changed in recent years, and the process now exists in most organizations to improve efficiency. The recruitment system is at the heart of every business, so ensuring consistency at every level is important to enhance effectiveness in hiring and retention.
Essay Contest Opens For High School Students NIH RecordMonica Waters
The article examines symbolic play in children with Autism Spectrum Disorder compared to typically
developing children. It found that children with ASD engaged in significantly less symbolic play and had
more difficulties with pretend play skills. The results suggest that assessing pretend play abilities can help
identify children with ASD and developing pretend play skills should be a focus of early intervention.
Edit My College Essay. 10 Most Common College EsMonica Waters
The document provides information about editing college essays through an online service. It outlines a 5-step process: 1) Create an account; 2) Complete an order form with instructions and deadline; 3) Review writer bids and choose one; 4) Review the paper and authorize payment; 5) Request revisions until satisfied. It emphasizes original, high-quality work and refunds for plagiarism.
1. The document discusses a website called HelpWriting.net that provides writing assistance services.
2. It outlines a 5-step process for using their services, which includes creating an account, submitting a request form, reviewing writer bids, authorizing payment, and requesting revisions.
3. They promise original, high-quality work and refunds for plagiarized content, aiming to fully meet customer needs.
Persuasive Writing Paragraph. How To Write AMonica Waters
The document discusses the impact of media on children's lives and socialization. It notes that media is an influential factor in socialization, especially for children. Media can positively impact children by exposing them to new ideas and information. However, excessive media use can negatively impact children's development by replacing social interactions and outdoor activities. The document calls for moderation and guidance when children consume media to maximize the benefits and minimize the risks.
How Does Nurture Influence Development. How Does NMonica Waters
The document discusses how nurture influences development through several steps:
1. Create an account on the site to request writing help
2. Complete an order form providing instructions, sources, deadline, and sample work
3. Review bids from writers and choose one based on qualifications to start the assignment
4. Review the completed paper and authorize payment if pleased, with options for revisions
5. Request multiple revisions to ensure satisfaction, with a guarantee of original work or a refund
View Formal Essay Examples For High SchooMonica Waters
The document provides instructions for requesting and completing an assignment writing request on the HelpWriting.net website. It outlines a 5-step process: 1) Create an account with an email and password. 2) Complete a 10-minute order form providing instructions, sources, and deadline. 3) Review bids from writers and choose one based on qualifications. 4) Review the completed paper and authorize payment if satisfied. 5) Request revisions until fully satisfied, with the option of a full refund for plagiarized work. The purpose is to outline the simple process for students to request writing help from the website.
1. Racism led to an unjust legal system where Tom Robinson, an innocent black man, was wrongly convicted of a crime and sentenced to death simply due to the color of his skin and prejudice of the all-white jury.
2. The racist attitudes prevalent in Maycomb caused Atticus to receive threats and face hostility from many in the town for agreeing to defend Tom Robinson, a black man.
3. Jem and Scout witnessed the ugly realities of racism through the mob that gathered outside the jail to lynch Tom Robinson before the trial, showing them the deep prejudice that existed. Racism shaped how the
The document discusses the steps to request writing assistance from HelpWriting.net:
1. Create an account with a password and valid email.
2. Complete a 10-minute order form providing instructions, sources, deadline, and attaching a sample for style imitation.
3. Review bids from writers for the request, choose one based on qualifications, and place a deposit to start.
4. Review the paper and authorize full payment if pleased, or request free revisions.
5. Multiple revisions are allowed to ensure satisfaction, and plagiarized work results in a full refund.
1) The U.S. already spends more on defense than the next several countries combined, indicating current spending levels are excessive.
2) Increasing defense spending would divert funding from critical domestic programs like education, healthcare, and infrastructure that Americans rely on.
3) With no major military threats on the horizon, additional defense spending provides few benefits while adding to the national debt burden.
Writing Cause And Effect Essay Examples - DefinitivMonica Waters
The passage discusses the Confucian philosophy and two influential Confucian thinkers, Mengzi and Xunzi. It notes that while Confucius sought to spread his teachings, later philosophers like Mengzi and Xunzi interpreted and debated his ideas, specifically around the question of whether human nature is inherently good or bad. The author argues against Mengzi's view that human nature is inherently good, instead asserting that it is completely self-interested.
How To Write A Compare And Contrast Essay Example. CMonica Waters
Here are a few key points about black women in America and their accomplishments:
- Bessie Coleman was the first African American and first Native American woman to hold an
international pilot license. She started her aviation career in 1921 after being denied flight lessons in
the U.S. due to her race and gender.
- Cathay Williams was the first African American woman to serve in the U.S. Army, enlisting in 1866
and serving until 1868. She disguised herself as a man in order to join.
- Madam C.J. Walker was America's first female self-made millionaire. She built a highly successful
business creating and selling hair care products for black women in the early
The document describes a 5-step process for obtaining writing assistance from HelpWriting.net:
1. Create an account with a password and email.
2. Complete a 10-minute order form providing instructions, sources, deadline, and sample work.
3. Choose a writer bid based on qualifications, history, and feedback, then pay a deposit.
4. Review the completed paper and authorize full payment or request revisions.
5. Request revisions to ensure satisfaction, and HelpWriting.net guarantees original, high-quality work with refunds for plagiarism.
How Serious Is Essay Plagiarism Students The GuardianMonica Waters
The document provides instructions for students to get writing help from HelpWriting.net. It outlines a 5-step process: 1) Create an account with an email and password. 2) Complete an order form with instructions, sources, and deadline. 3) Review bids from writers and choose one. 4) Receive the paper and authorize payment if satisfied. 5) Request revisions until satisfied, with a refund option for plagiarism. The process aims to ensure students get high-quality, original content through competitive bidding and revisions.
The document discusses drugs and alcohol in the criminal justice system. It notes that drug and alcohol abuse has long been part of human culture and American society. The period from 1950-2000 saw significant developments in how drugs and alcohol were viewed and addressed. Research and knowledge advanced, laws were passed, media coverage increased, and public views shifted. Overall, this time period was exceptionally active for American culture in terms of drugs and alcohol.
Essay Websites Examples Of Satire EssaysMonica Waters
The document discusses the author's experience visiting Yosemite National Park for the first time, expressing a sense of awe at the natural beauty of the park, including views of El Capitan. Yosemite National Park is located in California's Sierra Nevada mountains and was established in 1890 to protect its outstanding natural features spanning over 747,956 acres, including waterfalls, trees, cliffs and mountains. In just one hour at the park, the author was already amazed by what they had seen.
The document discusses the national nanotechnology initiative (NNI) and nanotechnology. It begins by defining nanotechnology as the study and manipulation of materials at the 1 to 100 nanometer scale, where materials exhibit novel properties due to their small size. It notes that the NNI was established to provide a general definition of nanotechnology. The document then discusses how nanoscience involves the study of nanomaterials, which have at least one dimension in the 1 to 100 nm range. It states that these nanomaterials have increased surface area and unique physical and chemical properties compared to larger materials.
Writing An Abstract For Your Research Paper The Writing Center UW ...Monica Waters
- AI systems in warfare could potentially reduce casualties by taking the place of human soldiers in dangerous situations. However, lethal autonomous weapons raise concerns about machines having the power to take human lives without meaningful human control.
- The opacity of advanced AI may make it difficult for humans to understand the system's decisions and determine accountability for any mistakes or ethical lapses. Without explainability, issues could arise regarding responsibility for the actions of AI systems.
- Developing AI for military use, including lethal applications, risks an arms race as nations work to gain strategic advantages over opponents. This could destabilize existing security frameworks and escalate conflicts.
Analytical Essay My First Day At School Short EssayMonica Waters
The document discusses a case study involving a business relationship between the author and Mr. Marshall. It began informally six months ago with the author supplying grapes to Mr. Marshall's health food store. Demand grew but issues arose regarding late or incomplete payments from Mr. Marshall. The author is considering ending the business relationship and asks what legal actions Mr. Marshall could take and what defenses they may have. Advice is sought on resolving disputes biblically to avoid negative impacts on both parties.
Assessment and Planning in Educational technology.pptxKavitha Krishnan
In an education system, it is understood that assessment is only for the students, but on the other hand, the Assessment of teachers is also an important aspect of the education system that ensures teachers are providing high-quality instruction to students. The assessment process can be used to provide feedback and support for professional development, to inform decisions about teacher retention or promotion, or to evaluate teacher effectiveness for accountability purposes.
A review of the growth of the Israel Genealogy Research Association Database Collection for the last 12 months. Our collection is now passed the 3 million mark and still growing. See which archives have contributed the most. See the different types of records we have, and which years have had records added. You can also see what we have for the future.
This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
Executive Directors Chat Leveraging AI for Diversity, Equity, and InclusionTechSoup
Let’s explore the intersection of technology and equity in the final session of our DEI series. Discover how AI tools, like ChatGPT, can be used to support and enhance your nonprofit's DEI initiatives. Participants will gain insights into practical AI applications and get tips for leveraging technology to advance their DEI goals.
Strategies for Effective Upskilling is a presentation by Chinwendu Peace in a Your Skill Boost Masterclass organisation by the Excellence Foundation for South Sudan on 08th and 09th June 2024 from 1 PM to 3 PM on each day.
ISO/IEC 27001, ISO/IEC 42001, and GDPR: Best Practices for Implementation and...PECB
Denis is a dynamic and results-driven Chief Information Officer (CIO) with a distinguished career spanning information systems analysis and technical project management. With a proven track record of spearheading the design and delivery of cutting-edge Information Management solutions, he has consistently elevated business operations, streamlined reporting functions, and maximized process efficiency.
Certified as an ISO/IEC 27001: Information Security Management Systems (ISMS) Lead Implementer, Data Protection Officer, and Cyber Risks Analyst, Denis brings a heightened focus on data security, privacy, and cyber resilience to every endeavor.
His expertise extends across a diverse spectrum of reporting, database, and web development applications, underpinned by an exceptional grasp of data storage and virtualization technologies. His proficiency in application testing, database administration, and data cleansing ensures seamless execution of complex projects.
What sets Denis apart is his comprehensive understanding of Business and Systems Analysis technologies, honed through involvement in all phases of the Software Development Lifecycle (SDLC). From meticulous requirements gathering to precise analysis, innovative design, rigorous development, thorough testing, and successful implementation, he has consistently delivered exceptional results.
Throughout his career, he has taken on multifaceted roles, from leading technical project management teams to owning solutions that drive operational excellence. His conscientious and proactive approach is unwavering, whether he is working independently or collaboratively within a team. His ability to connect with colleagues on a personal level underscores his commitment to fostering a harmonious and productive workplace environment.
Date: May 29, 2024
Tags: Information Security, ISO/IEC 27001, ISO/IEC 42001, Artificial Intelligence, GDPR
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Exploiting Artificial Intelligence for Empowering Researchers and Faculty, In...Dr. Vinod Kumar Kanvaria
Exploiting Artificial Intelligence for Empowering Researchers and Faculty,
International FDP on Fundamentals of Research in Social Sciences
at Integral University, Lucknow, 06.06.2024
By Dr. Vinod Kumar Kanvaria
This presentation was provided by Steph Pollock of The American Psychological Association’s Journals Program, and Damita Snow, of The American Society of Civil Engineers (ASCE), for the initial session of NISO's 2024 Training Series "DEIA in the Scholarly Landscape." Session One: 'Setting Expectations: a DEIA Primer,' was held June 6, 2024.
How to Add Chatter in the odoo 17 ERP ModuleCeline George
In Odoo, the chatter is like a chat tool that helps you work together on records. You can leave notes and track things, making it easier to talk with your team and partners. Inside chatter, all communication history, activity, and changes will be displayed.
1. International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Impact Factor (2012): 3.358
Volume 3 Issue 5, May 2014
www.ijsr.net
Licensed Under Creative Commons Attribution CC BY
A Study on Refrigeration
Poonam Dhankhar
M. Tech, G.J.U.S & T Hissar, Haryana, India
Abstract: Refrigeration is a basic method of food preservation. All the refrigeration methods for food preservation are based on
Reverse Carnot cycle, which explains Adiabatic and Isothermal Expansion and Compression. Basic components used in these cycles are
Evaporator, Compressor, Condenser and Expansion Valve. Generally used cycle is Vapor Compression Cycle. Other cycles are Vapor
Absorption Cycle, Gas Cycle. Other new methods of Refrigeration are Thermoelectric and Magnetic Refrigeration. Various types of
refrigerants are used in these cycles based upon their properties. Commercially Refrigeration is used as preservation method in various
food industries like Dairy and Meat Processing industry.
Keywords: Food preservation, reverse carnot cycle, evaporator, compressor, condenser, vapor compression cycle, Thermoelectric and
Magnetic Refrigeration
1. Introduction [1] [4]
Refrigeration is a process in which work is done to remove
heat from one location to another. Refrigeration has many
applications including but not limited to household
refrigerators, industrial freezers, cryogenics, air
conditioning, and heat pumps. In order to satisfy the Second
Law of Thermodynamics, some form of work must be
performed to accomplish this. The work is traditionally done
by mechanical work but can also be done by magnetism,
laser or other means. Since the turn of the century, there has
been steady growth of application of refrigeration in
preservation of perishable food products, agriculture and
fishery.
The purpose of refrigeration for food is to retard
deterioration by micro-organisms, chemical and physical
processes. By cooling at temperatures just above freezing it
is possible to achieve a limited extension of storage time
which is often sufficient for safe distribution and marketing.
By freezing to temperature as low as -30ᴼC, deterioration
can be slowed down further and this increases the storage
time. Refrigeration has applications in diverse industries,
such as manufacturing chemicals, petroleum, refineries,
paper and pulp industries also.
2. Review of Literature [6]
Ice harvesting:‐ The use of ice to refrigerate and thus
preserve food goes back to prehistoric times. Through the
ages, the seasonal harvesting of snow and ice was a regular
practice of most of the ancient cultures: Chinese, Hebrews,
Greeks, Romans, Persians. Ice and snow were stored in
caves or dugouts lined with straw or other insulating
materials. The Persians stored ice in pits called yakhchals.
Rationing of the ice allowed the preservation of foods over
the warm periods. This practice worked well down through
the centuries, with ice houses remaining in use into the
twentieth century. In the 16th century, the discovery of
chemical refrigeration was one of the first steps toward
artificial means of refrigeration. Sodium nitrate or
potassium nitrate, when added to water, lowered the water
temperature and created a sort of refrigeration bath for
cooling substances. During the first half of the 19th century,
ice harvesting became big business in America. New
Englander Frederic Tudor, who became known as the
"Ice King", worked on developing better insulation
products for the long distance shipment of ice, especially to
the tropics.
First refrigeration systems:- The first known method of
artificial refrigeration was demonstrated by William Cullen
at the University of Glasgow in Scotland in 1756. Cullen
used a pump to create a partial vacuum over a container of
diethyl ether, which then boiled, absorbing heat from the
surrounding air. The experiment even created a small
amount of ice, but had no practical application at that time.
In 1758, Benjamin Franklin and John Hadley, professor of
chemistry at Cambridge University, conducted an
experiment to explore the principle of evaporation as a
means to rapidly cool an object. Franklin and Hadley
confirmed that evaporation of highly volatile liquids such as
alcohol and ether could be used to drive down the
temperature of an object past the freezing point of water.
They conducted their experiment with the bulb of a mercury
thermometer. They lowered the temperature of the
thermometer bulb down to 7 °F (−14 °C) while the ambient
temperature was 65 °F (18 °C). Franklin noted that soon
after they passed the freezing point of water (32 °F) a thin
film of ice formed on the surface of the thermometer's bulb
and that the ice mass was about a quarter inch thick when
they stopped the experiment upon reaching 7 °F (−14 °C).
In 1820, the British scientist Michael Faraday liquefied
ammonia and other gases by using high pressures and low
temperatures.
An American living in Great Britain, Jacob Perkins,
obtained the first patent for a vapor-compression
refrigeration system in 1834. In 1842, an American
physician, John Gorrie, designed the first system for
refrigerating water to produce ice. His system compressed
air, then partially cooled the hot compressed air with water
before allowing it to expand while doing part of the work
required to drive the air compressor. That isentropic (the
process takes place from initiation to completion without an
increase or decrease in the entropy of the system, i.e., the
entropy of the system remains constant) expansion cooled
the air to a temperature low enough to freeze water and
produce ice, or to flow "through a pipe for effecting
Paper ID: 020132041 1212
2. International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Impact Factor (2012): 3.358
Volume 3 Issue 5, May 2014
www.ijsr.net
Licensed Under Creative Commons Attribution CC BY
refrigeration otherwise" as stated in his patent granted by the
U.S. Patent Office in 1851.Gorrie built a working prototype
(A prototype is an early sample or model built to test a
concept or process or to act as a thing to be replicated or
learned from), but his system was a commercial failure.
Alexander Twining began experimenting with vapor-
compression refrigeration in 1848 and obtained patents in
1850 and 1853. He is credited with having initiated
commercial refrigeration in the United States by 1856.
The first gas absorption refrigeration system using gaseous
ammonia dissolved in water (referred to as "aqua ammonia")
was developed by Ferdinand Carré of France in 1859 and
patented in 1860. Due to the toxicity of ammonia, such
systems were not developed for use in homes, but were used
to manufacture ice for sale.
Thaddeus Lowe, an American balloonist from the Civil
War, had experimented over the years with the properties of
gases. One of his mainstay enterprises was the high-volume
production of hydrogen gas. He also held several patents on
ice making machines. His "Compression Ice Machine"
would revolutionize the cold storage industry. In 1869 he
and other investors purchased an old steamship onto which
they loaded one of Lowe’s refrigeration units and began
shipping fresh fruit from New York to the Gulf Coast area,
and fresh meat from Galveston, Texas back to New York.
Because of Lowe’s lack of knowledge about shipping, the
business was a costly failure, and it was difficult for the
public to get used to the idea of being able to consume meat
that had been so long out of the packing house.
Domestic mechanical refrigerators became available in the
United States around 1911.
a) Widespread commercial use
By the 1870s breweries had become the largest users of
commercial refrigeration units, though some still relied on
harvested ice. Though the ice-harvesting industry had grown
immensely by the turn of the 20th century, pollution and
sewage had begun to creep into natural ice making it a
problem in the metropolitan suburbs. Eventually breweries
began to complain of tainted ice. This raised demand for
more modern and consumer-ready refrigeration and ice-
making machines. In 1895, German engineer Carl von
Linde set up a large-scale process for the production of
liquid air and eventually liquid oxygen for use in safe
household refrigerators.
Refrigerated railroad cars were introduced in the US in the
1840s for the short-run transportation of dairy products.
By 1900, the meat packing houses of Chicago had adopted
ammonia-cycle commercial refrigeration. By 1914, almost
every location used artificial refrigeration. The big meat
packers, Armour, Swift, and Wilson, had purchased the
most expensive units which they installed on train cars and
in branch houses and storage facilities in the more remote
distribution areas.It was not until the middle of the 20th
century that refrigeration units were designed for installation
on tractor-trailer rigs (trucks or Lorries). Refrigerated
vehicles are used to transport perishable goods, such as
frozen foods, fruit and vegetables, and temperature-sensitive
chemicals. Most modern refrigerators keep the temperature
between -40 and 20 °C and have a maximum payload of
around 24,000 kg gross weight (in Europe).
b) Home and consumer use
With the invention of synthetic refrigerants based mostly on
a chlorofluorocarbon (CFC) chemical, safer refrigerators
were possible for home and consumer use. Freon is a
trademark of the DuPont Corporation and refers to these
CFC, and later hydro chlorofluorocarbon (HCFC) and hydro
fluorocarbon (HFC), refrigerants developed in the late
1920s. These refrigerants were considered at the time to be
less harmful than the commonly used refrigerants of the
time, including methyl formate, ammonia, methyl chloride,
and sulfur dioxide. The intent was to provide refrigeration
equipment for home use without danger: these CFC
refrigerants answered that need. However, in the 1970s the
compounds were found to be reacting with atmospheric
ozone, an important protection against solar ultraviolet
radiation, and their use as a refrigerant worldwide was
curtailed in the Montreal Protocol of 1987.
3. Basic Refrigeration Principle [4] [5]
If you were to place a hot cup of coffee on a table and leave
it for a while, the heat in the coffee would be transferred to
the materials in contact with the coffee, i.e. the cup, the table
and the surrounding air. As the heat is transferred, the coffee
in time cools. Using the same principle, refrigeration works
by removing heat from a product and transferring that heat
to the outside air.
Refrigeration is used to cool products. The refrigeration
system (R) transfers heat from a cooler low-energy reservoir
to a warmer high-energy reservoir
Figure 1: Schematic representation of refrigeration
system
4. Refrigeration System Components [5]
There are five basic components of a refrigeration system,
these are: Evaporator, Compressor, Condenser, Expansion
Valve and Refrigerant- to conduct the heat from the product.
In order for the refrigeration cycle to operate successfully
each component must be present within the refrigeration
system.
Paper ID: 020132041 1213
3. International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Impact Factor (2012): 3.358
Volume 3 Issue 5, May 2014
www.ijsr.net
Licensed Under Creative Commons Attribution CC BY
4.1 The Evaporator
The purpose of the evaporator is to remove unwanted heat
from the product, via the liquid refrigerant. The liquid
refrigerant contained within the evaporator is boiling at a
low-pressure. The level of this pressure is determined by two
factors:
The rate at which the heat is absorbed from the product to
the liquid refrigerant in the evaporator
The rate at which the low-pressure vapour is removed
from the evaporator by the compressor
To enable the transfer of heat, the temperature of the
liquid refrigerant must be lower than the temperature of
the product being cooled. Once transferred, the liquid
refrigerant is drawn from the evaporator by the
compressor via the suction line. When leaving the
evaporator coil the liquid refrigerant is in vapor form.
4.2 The Compressor
The purpose of the compressor is to draw the low-
temperature, low-pressure vapour from the evaporator via
the suction line. When vapour is compressed it rises in
temperature. Therefore, the compressor transforms the
vapour from a low-temperature vapor to a high-temperature
vapour, in turn increasing the pressure. The vapor is then
released from the compressor in to the discharge line.
4.3 The Condenser
The purpose of the condenser is to extract heat from the
refrigerant to the outside air. Fans mounted above the
condenser unit are used to draw air through the condenser
coils. The temperature of the high-pressure vapour
determines the temperature at which the condensation
begins. As heat has to flow from the condenser to the air, the
condensation temperature must be higher than that of the air;
usually between - 12°C and -1°C. The high-pressure vapour
within the condenser is then cooled to the point where it
becomes a liquid refrigerant once more, whilst retaining
some heat. The liquid refrigerant then flows from the
condenser in to the liquid line.
4.4 The Expansion Valve
Within the refrigeration system, the expansion valve is
located at the end of the liquid line, before the evaporator.
The high-pressure liquid reaches the expansion valve,
having come from the condenser. The valve then reduces the
pressure of the refrigerant as it passes through the orifice,
which is located inside the valve. On reducing the pressure,
the temperature of the refrigerant also decreases to a level
below the surrounding air. This low-pressure, low
temperature liquid is then pumped in to the evaporator.
5. Methods of Refrigeration [4] [6]
Methods of refrigeration can be classified as;
Non-Cyclic
Cyclic
Thermoelectric
Magnetic Refrigeration
Other Methods
5.1 Non-cyclic refrigeration
In non-cyclic refrigeration, cooling is accomplished by
melting ice or by subliming dry ice (frozen carbon dioxide).
These methods are used for small-scale refrigeration such as
in laboratories and workshops, or in portable coolers. Ice
owes its effectiveness as a cooling agent to its constant
melting point of 0 °C (32 °F). In order to melt, ice must
absorb 333.55 kJ/kg (approx. 144 Btu/lb) of heat. Foodstuffs
maintained at this temperature or slightly above have an
increased storage life. Solid carbon dioxide has no liquid
phase at normal atmospheric pressure, so sublimes directly
from the solid to vapor phase at a temperature of -78.5 °C (-
109.3 °F), and is therefore effective for maintaining products
at low temperatures during the period of sublimation
(Sublimation refers to the process of transition of a
substance from the solid phase to the gas phase without
passing through an intermediate liquid phase). Systems such
as this where the refrigerant evaporates and is vented into
the atmosphere are known as "total loss refrigeration".
5.1.1 Ice Refrigeration
In this method the ordinary ice is used for keeping the space
at temperature below the surrounding temperature. The
temperature of ice is considered to be 0 degree Celsius hence
it can be used to maintain the temperatures of about 5 to 10
degree Celsius. To use the ice for refrigerating effect a
closed and insulated chamber is required. On one side of the
chamber ice is kept while on the other side there is a space
which is to be cooled where some material to be cooled can
be placed. If the temperature below 0 degree Celsius is
required, then the mixture of ice and salt is used. This
method of cooling is still being used for cooling the cold
drinks, keeping the water chilled in thermos, etc.
5.1.2 Dry ice refrigeration
Dry ice is the solid carbon dioxide having the temperature of
-78 degree Celsius. Dry ice converts directly from solid state
to gaseous; this process is called as sublimation. Dry ice can
be pressed into various sizes and shapes as blocks or slabs.
Dry ice is usually packed in the frozen food cartons along
with the food that has to be kept frozen for long intervals of
time. When the dry ice gets converted into vapor state it
keeps the food frozen. The process of dry ice refrigeration is
now-a-days being used for freezing the food in aircraft
transportation. The non-cyclic methods of refrigeration can
be used only in places where small amount of refrigeration is
required in places like laboratories, workshops, water
coolers, small old drink shops, small hotels etc.
5.2 Cyclic Refrigeration [2]
This consists of a refrigeration cycle, where heat is removed
from a low-temperature space or source and rejected to a
high-temperature sink with the help of external work, and its
inverse, the thermodynamic power cycle. In the power cycle,
heat is supplied from a high-temperature source to the
engine, part of the heat being used to produce work and the
rest being rejected to a low-temperature sink. This satisfies
the second law of thermodynamics.
Paper ID: 020132041 1214
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Paper ID: 020132041 1215
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Paper ID: 020132041 1216
6. International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Impact Factor (2012): 3.358
Volume 3 Issue 5, May 2014
www.ijsr.net
Licensed Under Creative Commons Attribution CC BY
The gas cycle is less efficient than the vapor compression
cycle. As such the working fluid does not receive and reject
heat at constant temperature. In the gas cycle, the
refrigeration effect is equal to the product of the specific
heat of the gas and the rise in temperature of the gas in the
low temperature side. Therefore, for the same cooling load, a
gas refrigeration cycle will require a large mass flow rate
and would be bulky.
Because of their lower efficiency and larger bulk, air cycle
coolers are not often used nowadays in terrestrial cooling
devices. The air cycle machine is very common, however,
on gas turbine-powered jet aircraft because compressed air is
readily available from the engines' compressor sections.
These jet aircraft's cooling and ventilation units also serve
the purpose of pressurizing the aircraft.
5.3 Thermoelectric refrigeration [1] [6]
Thermoelectric cooling uses the Peltier effect to create a heat
flux between the junctions of two different types of
materials. This effect is commonly used in camping and
portable coolers and for cooling electronic components and
small instruments.
5.4 Magnetic refrigeration [1] [6]
Magnetic refrigeration, or adiabatic demagnetization, is a
cooling technology based on the magnetocaloric effect, an
intrinsic property of magnetic solids. The refrigerant is often
a paramagnetic salt, such as cerium magnesium nitrate. The
active magnetic dipoles in this case are those of the electron
shells of the paramagnetic atoms.
A strong magnetic field is applied to the refrigerant, forcing
its various magnetic dipoles to align and putting these
degrees of freedom of the refrigerant into a state of lowered
entropy. A heat sink then absorbs the heat released by the
refrigerant due to its loss of entropy. Thermal contact with
the heat sink is then broken so that the system is insulated,
and the magnetic field is switched off. This increases the
heat capacity of the refrigerant, thus decreasing its
temperature below the temperature of the heat sink. Because
few materials exhibit the required properties at room
temperature, applications have so far been limited to
cryogenics and research.
5.5 Other Methods [1] [6]
Other methods of refrigeration include the:-
5.5.1)Air cycle machine: - An air cycle machine (ACM) is
the refrigeration unit of the environmental control system
(ECS) used in pressurized gas turbine-powered aircrafts. The
Air Cycle cooling process uses air instead of Freon in a gas
cycle
Paper ID: 020132041 1217
7. International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Impact Factor (2012): 3.358
Volume 3 Issue 5, May 2014
www.ijsr.net
Licensed Under Creative Commons Attribution CC BY
5.5.2) The vortex tube: - It is a mechanical device that
separates a compressed gas into hot and cold streams. It has
no parts. It is used for spot cooling, when compressed air is
available; and
5.5.3) Thermo acoustic refrigeration: - Thermo acoustic
engines are thermo acoustic devices which use high-
amplitude sound waves to pump heat from one place to
another. It is using sound waves in a pressurized gas to drive
heat transfer and heat exchange.
5.5.4)Steam jet cooling: - Steam jet cooling uses a high-
pressure jet of steam to cool water or other fluid media. Its
principle is, steam is passed through a vacuum ejector of
high efficiency to exhaust a separate, closed vessel which
forms part of a cooling water circuit. The partial vacuum in
the vessel causes some of the water to evaporate, thus giving
up heat through evaporative cooling. The chilled water is
pumped through the circuit to air coolers, while the
evaporated water from the ejector is recovered in separate
condensers and returned to the cooling circuit. Steam jet
cooling experienced a wave of popularity during the early
1930s for air conditioning large buildings. Steam ejector
refrigeration cycles were later supplanted by systems using
mechanical compressors.
6. Unit of refrigeration [6]
The units of refrigeration are always a unit of power.
Domestic and commercial refrigerators may be rated in kJ/s,
or Btu/h of cooling. For commercial and industrial
refrigeration systems most of the world uses the kilowatt
(kW) as the basic unit refrigeration. Typically, commercial
and industrial refrigeration systems North America are rated
in Tons of Refrigeration (TR). Historically, one Ton of
Refrigeration was defined as the energy removal rate that
will freeze one short ton of water at 0 °C (32 °F) in one day.
This was very important because many early refrigeration
systems were in ice houses. The simple unit allowed owners
of this refrigeration systems measure a days output of ice
against energy consumption and compare their plant to one
down the street. While ice houses make up a much smaller
part of the refrigeration industry than they once did the unit
of Tons of Refrigeration has remained in North America.
The unit's value as historically defined is approximately
11,958 BTU/hr (3.505 kW) has been redefined to be exactly
12,000 BTU/hr (3.517 kW).
While not truly a unit, a refrigeration system's Coefficient of
Performance (CoP) is very important in determining a
system's overall efficiency. It is defined as refrigeration
capacity in kW divided by the energy input in kW. While
CoP is a very simple measure, like the kW, it is typically not
used for industrial refrigeration in North America. Owners
and manufacturers of these systems typically use
Performance Factor. A system's Performance Factor is
defined as a system's energy input in horsepower divided by
its refrigeration capacity in Tons of Refrigeration. Both
Coefficient of Performance and Performance Factor can be
applied to either the entire system or to system components.
For example an individual compressor can be rated by
looking at the energy required to run the compressor versus
the expected refrigeration capacity based on inlet volume
flow rate. It is important to note that both Coefficient of
Performance and Performance Factor for a refrigeration
system are only defined at specific operating conditions.
Moving away from those operating conditions can
dramatically change a system's performance.
7. Assessment of Refrigeration [4]
7.1 TR
TR is the cooling effect produced is quantified as tons of
refrigeration, also referred to as “chiller tonnage.
§ TR = Q x Cp x (Ti – To) / 3024
Where Q is mass flow rate of coolant in kg/hr, Cp is coolant
specific heat in kCal /kg deg C, Ti is inlet temperature of
coolant to evaporator (chiller) in 0C, To is outlet
temperature of coolant from evaporator (chiller) in 0C.
1 TR of refrigeration = 3024 kCal/hr heat rejected
7.2 Specific Power Consumption
The specific power consumption kW/TR is a useful indicator
of the performance of a refrigeration system. By measuring
the refrigeration duty performed in TR and the kW inputs,
kW/TR is used as an energy performance indicator.
7.3 Coefficient of Performance
The theoretical Coefficient of Performance (Carnot), {COP
(Carnot), a standard measure of refrigeration efficiency of an
ideal refrigeration system} depends on two key system
temperatures:
Evaporator temperature (Te) and Condenser temperature
(Tc)
COP is given as: COP (Carnot) = Te / (Tc - Te)
This expression also indicates that higher COP (Carnot) is
achieved with higher evaporator temperatures and lower
condenser temperatures. But COP (Carnot) is only a ratio of
temperatures, and does not take into account the type of
compressor.
Hence the COP normally used in industry is calculated as
follows:
where the cooling effect is the difference in enthalpy across
the evaporator and expressed as kW.
Paper ID: 020132041 1218
8. International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Impact Factor (2012): 3.358
Volume 3 Issue 5, May 2014
www.ijsr.net
Licensed Under Creative Commons Attribution CC BY
8. Common Refrigerants [7]
There are several fluorocarbon refrigerants that have been
developed for use in VCRC.
Dichlorofluoromethane CCl2F2 R12
- used for refrigeration systems at higher
temperature levels typically, water chillers
and air conditioning.
has less chlorine, a little better for the
environment than R12 and used for lower
temperature applications
CHClF2 R22
tetrafluorethane - no chlorine ,it went into
production in 1991 and acted as replacement
for R12
CFH2CF3 R134a
Dichlorofluoroethane C2H3FCl2 R141b
corrosive and toxic, used in absorption
systems
NH3 Ammonia
behaves in the supercritical region, low
efficiency
CO2 R744
Combustible propane R290
9. How to Choose a Refrigerant [7]
Factors needed to be considered are Ozone Depletion
Potential, Global Warming Potential, Combustibility,
Thermal Factors.
Ozone Depletion Potential: these are chlorinated and
brominated refrigerants, acts as a catalyst to destroy ozone
molecules and reduces the natural shielding effect from
incoming ultra violet B radiation.
Global Warming Potential: Gases that absorb infrared
energy, with a high number of carbon-fluorine bonds and
generally have a long atmospheric lifetime.
Combustibility: All hydro-carbon fuels, such as propane
Thermal Factors:-The heat of vaporization of the
refrigerant should be high. The higher h(fg), the greater
the refrigerating effect per kg of fluid circulated. The
specific heat of the refrigerant should be low. The lower
the specific heat, the less heat it will pick up for a given
change in temperature during the throttling or in flow
through the piping and consequently the greater the
refrigerating effect per kg of refrigerant. The specific
volume of the refrigerant should be low to minimize the
work required per kg of refrigerant circulated. Since
evaporation and condenser temperatures are fixed by the
temperatures of the surroundings. Selection is based on
the suitability of the pressure-temperature relationship of
the refrigerant
Other factors include:‐ Chemical Stability, Toxicity,
Cost, Environmental Friendliness, Does not result in very
low pressures in the evaporator (air leakage), Does not
result in very high pressures in the condenser (refrigerant
leakage)
The vapor compression cycle is most commonly used for
refrigeration.
Comparison of vapor compression and gas compression
refrigerating cycles based on following parameters: [4]
1)Type of refrigerant used: In vapor compression cycle
liquids like Freon and ammonia are used as the refrigerant.
In the gas cycle the gas like air is used as the refrigerant.
2)Heat exchangers: In the vapor compression refrigeration
cycle condenser and evaporator are the two heat
exchangers where the refrigerant gives up and absorbs
heat respectively. The refrigerant undergoes change in
phase in both the heat exchangers. In the gas cycle the
refrigerant exchanges heat in the heat exchangers, but
there is no phase change of the gas.
3)Efficiency of the cycle: The efficiency of the vapor
compression cycle is more than that of the gas cycle. For
producing the same amount of refrigerating effect in the
gas cycle, large volume of gas is required; hence the
systems tend to become very large, bulky and expensive,
which are not affordable for the domestic applications.
4)Applications: The vapor compression cycle is most
widely used for the refrigeration purposes. It is used in
household refrigerators, air-conditioners, water cooler, ice
and ice cream makers, deep freezers, large industrial
refrigeration and air-conditioning systems, etc. Since the
size of the gas compression systems is very large, they are
not used for the domestic and industrial purposes. They
are used widely in the aircraft air-conditioning systems
since in aircrafts air at very high pressures is available
readily and there won’t be the need of air compressors.
This makes the air-conditioning system in the aircraft light
weight and less power consuming. The use of air as the
refrigerant in aircraft prevents the dangers of fire of from
the flammable refrigerants.
Differences between an absorption refrigeration system and
a VCRC [4]
Absorption RS VCRC
The refrigerant is absorbed by an
absorbent material to form a
liquid solution.
Vapour is compressed
between the evaporator
and the condenser.
Heat is added to the process to
retrieve the refrigerant vapour
from the liquid solution.
Process is driven by work
Process is driven by heat
10. Current Applications of Refrigeration [6]
Probably the most widely used current applications of
refrigeration are for the refrigeration of foodstuffs in homes,
restaurants and large storage warehouses. The use of
refrigerators in kitchens for the storage of fruits and
vegetables has permitted the addition of fresh salads to the
modern diet year round, and to store fish and meats safely
for long periods.
In commerce and manufacturing, there are many uses for
refrigeration. Refrigeration is used to liquefy gases like
oxygen, nitrogen, propane and methane for example. In
compressed air purification, it is used to condense water
vapor from compressed air to reduce its moisture content. In
oil refineries, chemical plants, and petrochemical plants,
refrigeration is used to maintain certain processes at their
required low temperatures (for example, in the alkylation of
butenes and butane to produce a high octane gasoline
component). Metal workers use refrigeration to temper steel
and cutlery. In transporting temperature-sensitive foodstuffs
Paper ID: 020132041 1219