Eliza-Rose Dang | Engineering Studies | 19/03/18

Refrigerator

0 | P A G E

Contents1.0 Introduction 22.0 History of the Refrigerator

2 2.1 Technological developments

2.2 Improving Functionality2.3 Methods of operation2.4 Societal Changes

3.0 Impact of the Refrigerator5

3.1 The Individual3.2 Society3.3 The Environment

4.0 Components of a Refrigerator8

4.1 The Condenser4.1.1 Image4.1.2 Materials4.1.3 Forming Process4.1.4 Mechanical Properties

4.2 The Evaporator4.2.1 Image4.2.2 Materials4.2.3 Forming Process

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4.2.4 Mechanical Properties4.3 The Compressor

4.3.1 Image4.3.2 Materials4.3.3 Forming Process4.3.4 Mechanical Properties

5.0 Operation of a Refrigerator5.1 Defrost System

5.1.1 Defrost Cycle5.1.2 Cooling Cycle

5.2 Control Functions6.0 Engineers

6.1 Type of Engineer6.2 Contribution to the invention of the Refrigerator6.3 Engineering courses in Australia

7.0 Orthogonal Drawing8.0 References

1.0 IntroductionRefrigeration is the process of removing heat from an enclosed space or

from a substance to lower its temperature. It is the process of heat transfer against the natural flow of heat which is from high to low temperature. A household refrigerator has been referred to as one of the greatest unsung inventions. Professor Benjamin Nagengast of the Hector Research Institute quotes “The household refrigerator changed the way people ate and socially affected the household. They were no longer dependent on ice delivery and they didn’t have to make provisions for it like leaving a key or the door open.”

Refrigeration has developed into something that is reliable and inexpensive enough for widespread ownership and use. Modern refrigeration has improved peoples diet, lifestyle and the concept of freshness.

The refrigerator mainly uses three main components, the evaporator, condenser and compressor. The refrigerant (HFC’s) start in the compressor which

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compressors the gas and then move through the condenser coils where it condenses the gas into a liquid, and heat is dissipated through the air. It then passes through the expansion valve before entering the evaporator coils where it turns back into a cooler liquid and circulates through the refrigeration unit and cools down the substances inside.

This report consists of the Historical developments of the refrigerator, impacts of the refrigerator on individuals, society and the environment. It also explains the three main components of a refrigerator and the electronic operations of the refrigerator including the cycles and the function controls and the types of engineers involved in creating the refrigerator. This is then finished with an orthogonal drawing with three different views (top, front, right).

2.0 History of the Refrigerator

2.1 Technological DevelopmentsIce was the primary means of refrigeration until the 19th century. Many of the western countries used ice boxes or ice chests were used to keep foods fresh. They a double layered box, made from a wood, usually mahogany, on the outer layer of the box, then the inner layer was made from a metal sheet, usually zinc or tin with about 9-10cm of space in between the two layers. This space was filled with finely powdered charcoal, well-packed together to provide insulation. They then later started to use other materials such as, fur, pelt, hair, cork, wool, felt and asbestos. The insulation process for ice-boxes had not yet been standardised. This rendered the ice-box heat proof. Then a lump of ice between 2-3kg was placed on a shelf at the top of the ice box with a pipe that ran from the top of the unit to the bottom that allowed the water to drip down to a tray underneath the ice-box. The ice tray had to be emptied daily. This allowed the ice to be kept for 24 – 36 hours. There were shelves inside the ice box so that dishes, bowls and pitchers could be placed in the ice-box.

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This is a diagram of an ice-box with the compartment for ice at the top and the simple interior.

A simple diagram showing the basic way a refrigerator works

The first attempt at the modern, artificial refrigerator took place at the University of Glasgow in Scotland by William Cullen in 1748. He revived the Indian-Egyptian practice of freezing liquid through evaporation, although he accelerated this process by boiling ethyl ether, (“a pleasant-smelling colourless volatile liquid that is highly flammable. It is used as an anaesthetic and as a solvent or intermediate in industrial processes”) into a partial vacuum. This was simply the first experiment in the history of inventing the modern refrigerator. In the year 1805, American inventor, Oliver Evans designed the first refrigerator that used vapour instead of liquid to cool. His machine was based on a closed cycle of compressed ether, this was the first effort of using a simple vapour instead of vaporising liquid. Evan’s machine never developed beyond the prototype stage.

In 1844 and American doctor, John Gorrie, built a very similar machine to Evan’s prototype, to provide ice for the hospital in which he worked, and to cool down the air for yellow fever patients. His machine compressed air that was next to the machine cooled with water. The cooled air was then routed into an engine cylinder and as it re-expanded, it’s temperature dropped enough so that ice could be made. In 1857, Australian inventor James Harrison invented the first ice making machine used for food purposes such as meat-packing and brewing.

Then in 1859, the same concept was made more complex by inventor Ferdinand Carre. This new system didn’t use compressed air to cool but instead used ammonia as a coolant. The use of ammonia represented an advance because of it expands more rapidly than water and can thus absorb more heat from its environment. The refrigerator he invented operated by means of a cycle, in which the refrigerant (ammonia) was absorbed in a liquid (water and ammonia) that was then heated. This caused the refrigerant to evaporate, thereby creating a cooling effect, then after the refrigerant was condensed the cycle could then be repeated. Carre’s machine sold extremely well. These components remain the basis of modern refrigeration today.

Later in 1876, a German engineer Carl Von Linden, established to process of liquifying gas, which is a crucial aspect of refrigeration technology. In 1927 the first widely used refrigeration system was released in 1927 by General Electric.

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Sketch of Dr John Gorrie’s mechanical ice machine

Advertisement for the first refrigerator released by General Electric in 1927

2.2 Improving FunctionalityThe functionality of the Refrigeration has improved significantly over the past 150 years. The first attempt at modern refrigeration used liquid. They evaporated the liquid which would then created a freezing effect, which created the first artificial ice. This was then improved upon by many other inventors and engineers, where they started to compress air, which was cooled with water and moved into an engine cylinder and as the cooled air re-expanded it temperature dropped enough so that ice could be made.

Modern Refrigeration companies are now concerned with aesthetics and functionality. Early refrigerators resembled ice-boxes with wooden bodies and simple interiors. Issues that are now important to a consumer are increased food storage, greater cooling capacity, improved appearance, reduced energy consumption, lower noise level and lower cost. All refrigerators were made with enamelled metal, stylistic features and interiors were designed with convenience in mind, by the 1930’s. In 1933, the first door shelves were patented by the company Crosley. By the 1940’s freezer compartments had a mechanical release, ice trays, butter trays with a higher temperature to keep the butter spreadable, rust proof shelving, left and right hand opening doors, utility shelves for bottles and meat trays and vegetable drawers.

2.3 Methods of OperationThe primary means of refrigeration today is generated through the rapid expansion of that gases. The gas first evaporates at an extremely low temperature creating freezing temperatures inside the refrigerator. Then the liquid is then rapidly vaporised through a compressor. The expanding vapour then uses kinetic energy, which draws the energy away from the immediate area, the gas then loses energy and therefore cools down the gas. This then continues in a constant cycle.

There have been many different refrigerants used previously. The first refrigerant used was Ethel ether which was used by boiling the into a partial vacuum. Then followed using a simple vapour, instead of vapouring a liquid. Different engineers also tried compressed air. Using ammonia as a refrigerant had the most success during the late 19th and early 20th century. Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is a colourless gas with a pungent smell. Ammonia poses several problems, however it posed as a very effective coolant. It was very poisonous when

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General Electric refrigerator from the 1940’s

leaked and caused many deaths during the early 20th century. It then very quickly disappeared from refrigeration after synthetic alternatives were invented in the 1920’s.

The most well know of these was Chlorofluorocarbons (CFC’s) patented by Du Pont under the name Freon. They were made by adjusting the methane molecule, substituting the two chlorine atoms and two fluorine atoms for four hydrogen atoms. The gas was then widely used because of its low boiling point, viscosity and surface tension which rendered it the ideal refrigerant. Scientists then later realised the environmental impact this had on the ozone layer and the UN is currently trying the phase out the manufacturing of CFC’s. The current gas being used in refrigerators is hydrofluorocarbons (HFC’s), although this isn’t doing damage to the ozone layer it does have other environmental impacts that the US government is trying to phase down the production of HFC’s.

2.4 Societal changesAll throughout history until the late 19th century, the means of refrigeration was through using snow or ice. This ice was either found locally or sourced from the mountains. People would then dig holes in the ground and lined them with wood or straw then packed the snow or ice into the hole. Then they started using ice-boxes, but this still required that ice be delivered to households regularly. This still was not convenient for families and in 1890 there was a shortage of natural ice, which fast forwarded the invention of refrigerators as they needed to quickly find a mechanical means of making ice. Refrigerators were the by-product of a desire to create ice commercially with a growing interest to ship fresh produce overseas. In the United States, in 1923 ice boxes outsold refrigerators but by 1944 refrigerators were outselling ice boxes in a ratio of two to one.

3.0 Impacts of the Refrigerator3.1 The Individual

The use of ice in the home was rapidly growing and by the 1920’s a refrigerator was an essential piece of kitchen furniture. In 1921, 5000 mechanical refrigerators were manufactured in the United states, then ten year later that number grew past one million and just six years after that nearly six million refrigerators were being manufactured every year. By

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At a 1925 ice harvest in Maine, men separated the cut ice

1950, more than 90% of urban homes and 80% of American farms owned a refrigerator.

Refrigerators provided convenience to individuals and families globally. No longer were people dependent on ice delivery daily and they were no longer having to make provisions for the ice like leaving their house open or leaving a key. It also provided a change in diet for people. Suddenly people were able to eat a wider variety of foods and keep them fresher for longer. Before refrigeration peoples diet consisted mainly of bread and slated meats, but the invention of refrigeration meant that people were able to diversify their diet and eat different foods, like, fresh meat, fish, milk, fruits and vegetables. Before mechanical refrigeration food preservation used the time-tested methods: salting, smoking, spicing, drying and pickling, but none of these methods were able to prevent rapid spoilage.

3.2 SocietyRefrigeration had a very significant impact on society, it provided economy growth, grew major cities, reformed industries and allowed for the widespread distribution of fresh foods. Refrigeration became an industry itself, and it tore down the barriers of climate and seasons.

The main industries that refrigeration changes were the brewing and meat packing industries. Refrigeration allowed breweries to create a uniform beer all year round. They were first industry to use mechanical refrigeration on a commercial scale. By 1891 every brewery had refrigerating machines.

By 1914, every meat packing plant had refrigerators that used the ammonia compression system, these refrigerators had a capacity of 90 000 tonnes. They were essential for the distribution of perishable foods on a widespread scale. Curing meat was now all year round as animals could be brought to the market at any time and meat quality also drastically improved.

Many other industries also caught on to use refrigerators. Metal working used them to temper cutlery and tools, iron production, removing moisture and to blast their furnaces. The other industries that started using refrigeration are: oil refineries, textile mills, paper, drugs, soap, glue, shoe polish, perfume, celluloid, photographic materials, fur and woollen goods, nurseries and florists, morgues, sugar mills, chocolate factories, bakeries, tea companies, hospitality and in defence using them in munitions factories.

By 1860, refrigerated transport was limited to seafood and dairy products. A refrigerated railroad car was invented and patented by J.B.Sutherland from Detroit, Michigan. He designed and insulated car with ice bunkers. Air came into the car from the top, passed through the bunkers and circulated

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An example of the early refrigerated rail road car (1870)

through the car by use of gravity. The use of the controlled hanging flaps that created differences in air temperature. The cars created the ability for people to distribute regional fresh produce into major cities, which helps to create healthier diets for the general population.

3.3 The Environment

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Mechanical refrigeration had a very significant impact on the environment. Early mechanical refrigerators used ammonia, a highly toxic gas. A series of

fatal accidents in both the home and workplace in the 1920’s, which then

encouraged researchers to find another alternative refrigerant. This then lead them to develop the gas Freon, also known as Chlorofluorocarbons (CFC’s). this extremely stable, chemically inert, non-toxic and non-flammable gas was used by all refrigerator companies. They were used until the 1980’s when it was brought to public attention that they had a

devastating affect on the ozone layer. Researchers than had to develop a non-toxic, environmentally friendly alternative. They came up with Hydrofluorocarbons (HFC’s) are currently being used as refrigerants. HFC’s now pose a rapidly growing climate threat. They emit heat trapping gases during manufacturing, leakage and disposal. HFC’s are safer for the ozone layer but not necessarily for the planet, they’re nearly 10 000 times as potent as carbon dioxide. “Though HFC’s currently represent a small fraction of the total greenhouse gas emissions, their global warming potential is very high, and their emissions could rise even up to 40% of annual carbon dioxide emissions by the middle of the century if society

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The graph (above) shows the predicted levels of Hydrofluorocarbons in the atmosphere by 2030 showing it in million metric tons of carbon dioxide

continues,” Steiner said in a keynote address at the meeting. HFC’s contribute the greenhouse effect in the globe and the emissions could double by 2020 and triple by 2030, according to US data. The United States is currently trying to find a safer alternative. Propane is the newly approved refrigerant in replacement of HFC’s.

4.0 Components of a Refrigerator4.1 Condenser

Component/Image Materials Forming Processes

Properties

Condenser: the compressor compresses the gas refrigerant through the condensing coils and condenses it to a liquid. Heat is dissipated through the atmosphere.

Condensers are the heat exchangers of the refrigerators. They are usually made of iron or copper tubes in a serpentine shape and welded together with properly spaced iron wires. There are three main types of condensers, The Evaporative Type:It is housed inside a steel housing with four feet, the gas discharges through the top of the unit.The Air-cooled Type: They are housed inside a steel unit with an open top and bottom, cooled by natural circulation of the air.The Water-cooled type: The coils are housed inside a cylinder, water enters through the inlet

The evaporator is welded together with properly spaced iron wires. The welding method used to form the pipes is Gas or Oxy Acetylene Welding and Cutting. This consists of mixing acetylene gas and oxygen to create a flame capable of melting steels. This method is most commonly used for brazing softer metals. The wires are folded into a serpentine U shape to allow for the cross flow of air through and around the coils.

There are many mechanical properties of the condenser. The pipes have good tensile and creep properties making them adequately ductile, with a high rupture strength. They also have a good fatigue and corrosion fatigue behaviour. The pipes also have a good fracture strength and impact strength to avoid fast fracture.They also have many physical properties that make them suitable to a refrigerator. The pipes have a high transfer heat rate as they require a high thermal conductivity.

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pipe, circulates around the coils and discharges towards the outlet pipe.

4.2 EvaporatorComponent/Image Materials Forming

ProcessesProperties

Evaporator: they absorb the heat inside the refrigerator and change the liquid refrigerant into gas.

Evaporators are made from coils of aluminium tubing, they can usually be found at the back or under the refrigerator compartment. The aluminium coils absorb the heat inside the refrigerator, it changes the liquid refrigerant into gas. The coils are classified into two types, the flooded type and the dry type:The Flooded Type: this type uses the accumulator above the coil to store the refrigerant in the form of the liquid. The Dry type:

Evaporators are made through a serpentine U-Shape that moves through finned aluminium. The Serpentine shape would have been formed in a similar way to the condenser, using the welding method Gas or Oxy Acetylene Welding and Cutting. With aluminium being a softer metal, this would have provided a suitable welding method for the serpentine shape of the coils. The fins are shaped around the coils and they are connected to the back piece of the evaporator is made

There are many useful thermal properties of Evaporators that make them suitable for use in a refrigerator. Like the condenser the pipes would have a good fracture strength and impact strength to avoid fast fracture. They would also have good corrosion and fatigue properties which would help them to avoid fast fracture. The evaporators would also have good thermal properties,

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This type is a system that only allows enough liquid refrigerant mist to enter the coils, and to be completely evaporated when it reaches the end of the tube.

from aluminium and the metal is moulded into poles that are welded into a frame where the fins are the placed horizontally along each of the poles.

including thermal conductivity to allow for heat transfer within the unit.

4.3 CompressorComponent/Image Materials Forming

ProcessesProperties

Compressor: they are referred to as the “heart” of the refrigerator. The compressor circulates the refrigerant gas to perform the refrigeration cycle repeatedly

The outside of the compressor has a steel or titanium casing. For a high-performance compressor, the materials that it is made from need to be light weight with an increased strength and increased strength and stiffness. Inside the casing there is an electric motor, a cylinder piston, a crankshaft, connecting rod, intake and exhaust valves and a ceramic terminal block. Each compressor also contains about 500mL of Capella Oil. Capella oil is used is refrigerators as it has a low wax content, low moisture content and it is chemically stable in the presence of

The suction copper tube of a compressor has a large diameter and the discharge tube has a smaller diameter. Some compressors have two extra copper tubes on the lower side of the compressor and they are the oil cooling tubes. There are three rubber brushings in each compressor, they are the vibration dumpers and decrease the noise pollution from the refrigerator. The outside of the compressor is welded or screwed together to prevent any heat or cool air from escaping and the inside is made in such a way that provides energy efficiency and noise reduction.

The compressor is sealed air tight which would prevent any air or gas from escaping the unit while it is being compressed. They have a very tough and strong outer shell to prevent it from fast fracture. The outer shell of the compressor also has good stiffness from the metal. The outer shell also has good corrosion and fatigue properties to prevent the stress from breaking the shell.

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refrigerants.

5.0 Operation of a RefrigeratorThere are two main components of the in a refrigerator defrost system. There is the defrost cycle and the cooling cycle. These cycles ensure that the frost-free system works seamlessly. The most common control is a mechanical defrost timer which will open and close through several electrical contacts. Each of the contacts can be referred to as a simple light switch, but instead of a light one connects the defrost switch on and the other is off.

5.1 Defrost System5.1.1 Defrost Cycle

In the defrost cycle the timer eventually switches into defrost mode and will then supply power to the defrost heaters that has accumulated on the evaporator. The cold control will remain closed but since the defrost timer is no longer feeding power to that circuit, the compressor does not run. Once the defrost limit switch detects a set temperature it opens the circuit to the defrost heaters, turning them off. The timer will then remain in the defrost cycle until the timer then return to cooling mode.

5.1.2 Cooling Cycle

During the cooling cycle the defrost timer closes a contact to the compressor circuit so that it will run. The circuit to the defrost heater is then open. When the timer returns to the cooling cycle, the compressor will start to run, the defrost limit switch will stay open until it is reset by cold temperatures. Once the colder temperature is reached, the defrost limit switch closes (defrost thermostat). When the defrost timer advances into the defrost cycle the limit defrost switch will already be closed and will then allow the power to be supplied to the defrost heater to melt any frost that has developed on the evaporator coil.

5.2 Control FunctionsIn today’s digital age there are many intellectual control functions that can be found in a refrigerator. It is the inevitable trend for home appliances. The

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The diagram above shows the electronic circuitry of the defrost cycle

The diagram above shows the electronic circuitry of the cooling cycle

controller of the variable frequency of the can adjust some rotating components including the motor in the compressor, to best fit the customer and environmental condition. There are now sensor-less control circuits and machine codes for a refrigerant compressor, power supply and transformer with power factor correction, ability to defence of electromagnetic interference and some analogue sensors or communication. These better control methods could serve with higher performance and behave friendly for a wider range of consumers with household appliances.

There are inputs for the defrost control method. The input signals are coming from the temperature transducers, electro switches like doors or function bottoms, and timer for defrosting or adaptive control. The output signals regulate suitable actions for the compressor, chilled flow electro damper and defrosting heater. The amplitude of these control systems is decided following consumer’s capability.

The defrost control method is the determination of the starting time and defrosting duration for an electric heater below the evaporator in the freezer compartment. There are many ways to judge the starting time for defrosting. Different types of sensors inside the evaporator to detect frost thickness or temperature difference between frost and fins. The frost’s formation is very complicated, and this is a simple method by the regular defrosting cycle usually consumes more energy than necessary. The flowchart below shows the control sequence for each component associated with the defrosting process including the compressor, motor of the evaporator, timer and defrosting electric heater.

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The flow chart (right) shows the defrost control method for a refrigerator

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Another function control is the door opening control method. When a refrigerator door is open, moist, warm air enters the refrigerator compartment and will also increase the heat load in comparison to a closed refrigerator. If it is open for more than half a minute, it will start to affect the freshness of the stored food. The refrigerator will need additional cooling capability to cope with the additional heat load. As doors are open for a long time, action of door switches will start the clock inside the controller and judge the compressors speed to provide available cooling capacity. For the door opening control method a switch will detect the door opening status. To prevent thermal entrance a circulation fan in compartments will stop as the door is open. The controller will then start to calculate door opening time and regulates the necessary running speed and corresponding frequency for inverter-controlled compressor. The highest speed should be maintained to overcome continuous thermal entrance. After the door has been closed the fan motor will then resume and the door opening time will be reset to zero. For some refrigerators an alarm or voice function is built-in the confirm the doors being closed after using. The flowchart below shows the function of the door opening control method.

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The flow chart (right) shows the Door opening control method for a refrigerator

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The final control method is the frozen food storage temperature control method. For some fixed frequency types of refrigerators and freezers the frozen food storage temperature is maintained by turning on/off for a compressor from the criteria of freezing

temperature difference (DTf) between setting value of the compartment bottom Tfs and the actual value read by Tf inside the freezer compartment. They generally used a pre-defined methodology to maintain constant temperature and to also reduce the cycling loss. It is important to have a functional relationship between the DTf and the compressor rotation frequency (Fz), this was established during the products development as

Fz=f (DTf ). The controller sends out a signal following this relationship to the driver of the compressor then the suitable rotation speed can then be calculated and achieved. For different operation conditions a variable speed compressor will implement different control functions for customers.

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6.0 Engineers involved in making the RefrigeratorThere are many different types of engineers involved in making a refrigerator. The first is an Electrical engineer. The electrical engineer would have contributed to the making of the electrical components of the refrigerator. Many refrigerators ow also contain an electrical component which allows the refrigerator to run on electricity. There are many electoral engineering courses in Australia. The University of New South Wales in Sydney, offer multiple courses in Electrical Engineering, the main one is an Engineering(Hons)/Master of Engineering in Electrical Engineering.

Another type of engineer that would have contributed to the making of a refrigerator is a Thermal Engineer which is a sub-discipline of Mechanical Engineering. Thermal Engineers would have contributed to the outer structure or the refrigerator, this means they would have helped to make the shell of the refrigerator as this would have needed to have thermal properties. There are very few courses in Australia that offer a degree in Thermal Engineering. At RMIT Melbourne a double degree can be studied of a Bachelor of Engineering(Hons)/advanced manufacturing and mechatronics.

7.0 Orthogonal Drawing: Expansion Valve

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The flow chart (right) shows the Frozen food storage temperature control method for a refrigerator

8.0 ReferencesAdrimaal.D.M & Bullard.C.W 1993, Heat Transfer in Refrigerator Condensers and Evaporators. viewed 16 March 2018. < https://www.ideals.illinois.edu/bitstream/handle/2142/9750/TR048.pdf >

Advameg 2018, Refrigerator. viewed 9 March 2018 < http://www.madehow.com/Volume-1/Refrigerator.html >

Bachelor of Engineering (Adv Manufacturing and Mechatronics) (Honours), 2018. RMIT University. viewed 15 March 2018 < https://www.rmit.edu.au/study-with-us/levels-of-study/undergraduate-study/honours-degrees/bh068 >

Bellis.M 2006. The History of the Refrigerator and Freezers. viewed 19 Feb 2018, < http://theinventors.org/library/inventors/blrefrigerator.htm >

Bellis.M 2017. The History of the Refrigerator and Freezers. viewed 19 Feb 2018, < https://www.thoughtco.com/history-of-refrigerator-and-freezers-4072564 >

Brain.M & Elliot.S 2018, How Refrigerators Work, viewed 22 Feb 2018. < https://home.howstuffworks.com/refrigerator2.htm >

Chang.W, Liu.D, Chen.S & Wu.N 2004, The Components and Control Methods for Implementation of Inverter-Controlled Refrigerators/Freezers, Energy and Resource Laboratories (ERL). Industrial Technology and Research Institute (ITRI),viewed 9 March 2018 < https://docs.lib.purdue.edu/cgi/viewcontent.cgi?referer=https://www.google.com.au/&httpsredir=1&article=1695&context=irac >

Capella® WF. 2018, Chevron Marine Lubricant. viewed 17 March 2018. < http://www.chevronmarineproducts.com/en_UK/products/pds-product-details/capella-wf-pds.html >

Electrical Engineering (Hons), 2018, UNSW Sydney. viewed 15 March 2018 < https://www.futurestudents.unsw.edu.au/degreetool/engineering/electrical-engineering-hons >

Ether Definition. 2018, Oxford Dictionary. viewed 11 March 2018, < https://en.oxforddictionaries.com/definition/ether >

Evaporator for a Refrigerator and the Method for the production thereof, 2014, United States Patent. viewed 18 March 2018. < https://patentimages.storage.googleapis.com/c2/fd/ca/116dcdf2c8f55a/US8701749.pdf >

Hertzman.P 2016, The Refrigerator Revolution. Dublin Gastronomy Symposium. viewed 11 March 2018. < https://arrow.dit.ie/cgi/viewcontent.cgi?referer=https://www.google.com.au/&httpsredir=1&article=1093&context=dgs >

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Institutions offering Engineering. 2018. viewed 23 Feb 2018. < https://www.hotcoursesabroad.com/study/training-degrees/australia/chemical-engineering-courses/loc/9/cgory/yc.1-4/sin/ct/programs.html >

Jester.H 2015. Refrigeration Changed ... Everything. viewed 23 Feb 2018, < http://web.colby.edu/humanslashnature/2015/10/06/refrigeration-changed-everything/ >

Khemani.H 2016, How Does A Refrigerator Work: Components of the Refrigeration Cycle. viewed 22 Feb 2018, < http://www.brighthubengineering.com/hvac/856-how-does-a-refrigerator-work-components-of-the-refrigeration-cycle/ >

Krasner-Khait.B The impact of Refrigeration. viewed 23 Feb 2018. < https://www.history-magazine.com/refrig.html >

Koch.W 2015, Why Your Fridge Pollutes and How it's Changing. viewed 23 Feb 2018, < https://news.nationalgeographic.com/news/energy/2015/03/150306-why-your-fridge-pollutes-and-how-its-changing/ >

Major Appliances, Major History - the Refrigerator & Freezer, 2018. viewed 19 Feb 2018. < https://www.partselect.com/JustForFun/Major-History-The-Refrigerator-And-Freezer.aspx >

O'Niell.D 2018, How does a frost free refrigerator's defrost system work? Appliance 411 Information. viewed 18 March 2018, < http://www.appliance411.com/faq/howdefrostworks.shtml >

Refrigerator Components, Freezer Components. 2009. viewed 22 Feb 2018, < https://www.air-conditioning-and-refrigeration.com/Refrigerator-components.html >

Rodriguez.P 1997, Selection of Materials for Heat Exchangers. Indira Gandhi Center for Atomic Research. viewed 11 March 2018, < http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/29/000/29000411.pdf  >

Sforza.N 2018, How Does a Refrigerator Work? viewed 22 Feb 2018, < https://www.realsimple.com/food-recipes/tools-products/appliances/how-does-refrigerator-work >

Smith.C 2018, Domestic Refrigeration & Refrigerators. viewed 19 Feb 2018, < https://collections.museumvictoria.com.au/articles/710 >

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