A typical American refrigerator with its door open

A refrigerator (often called a "fridge" for short) is a cooling appliance comprising a thermally insulated compartment and a mechanism to transfer heat from it to the external environment, cooling the contents to a temperature below ambient. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer Refrigerators are extensively used to store foods which deteriorate at ambient temperatures; spoilage from bacterial growth and other processes is much slower at low temperatures. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have A device described as a "refrigerator" maintains a temperature a few degrees above the freezing point of water; a similar device which maintains a temperature below the freezing point of water is called a "freezer". Freezing Point (Chinese 冰點 Bīngdiǎn is a news journal in the People's Republic of China which has been the subject of controversy over its criticism The refrigerator is a relatively modern invention amongst kitchen appliances. Home appliances are electrical/mechanical Appliances which accomplish some Household functions such as Cooking or cleaning. It replaced the common icebox which had been placed outside for almost a century and a half prior, and is sometimes still called by the original name "icebox". An Icebox was the common appliance for providing Refrigeration in the home before safe refrigerants made compact mechanical Refrigerators useful

Freezers keep their contents frozen. They are used both in households and for commercial use. Most freezers operate at around -18 °C (0 °F). Domestic freezers can be included as a compartment in a refrigerator, sharing the same mechanism or with a separate mechanism, or can be standalone units. Domestic freezers are generally upright units, resembling refrigerators, or chests, resembling upright units laid on their backs. Many modern freezers come with an icemaker. An icemaker is a device often found inside a Freezer that is used to make Ice.

Commercial fridge and freezer units, which go by many other names, were in use for almost 40 years prior to the common home models. They used toxic ammonia gas systems, making them unsafe for home use. Practical household refrigerators were introduced in 1915 and gained wider acceptance in the United States in the 1930s as prices fell and non-toxic, non-flammable synthetic refrigerants such as Freon or R-12 were introduced. A refrigerant is a compound used in a heat cycle that undergoes a Phase change from a Gas to a Liquid and back Freon is DuPont 's trade name for its odorless colorless nonflammable and noncorrosive Chlorofluorocarbon and Hydrochlorofluorocarbon Refrigerants It is notable that while 60% of households in the US owned a refrigerator by the 1930s, it was not until 40 years later, in the 1970s, that the refrigerator achieved a similar level of penetration in the United Kingdom. ^[1]

History of the refrigerator

See also: Timeline of low-temperature technology

Before the invention of the refrigerator, icehouses were used to provide cool storage for most of the year. Timeline of low-temperature Technology and Cryogenic technology ( Refrigeration down to (–150 °C –238 °F or 123 K and Ice houses were buildings used to store Ice throughout the year prior to the invention of the Refrigerator. Placed near freshwater lakes or packed with snow and ice during the winter, they were once very common. Using the environment to cool foodstuffs is still common today. On mountainsides run off from melting snow higher up is a convenient way to cool drinks, and during the winter months simply placing one's milk outside one's window is sufficient to greatly extend its useful life.

The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in 1748. William Cullen ( 15 April 1710 – 5 February 1790) was a Scottish doctor and Chemist. The University of Glasgow (Oilthigh Ghlaschu was founded in 1451 in Glasgow, Scotland and along with its contemporary institutions the University of St Andrews Between 1805, when Oliver Evans designed the first refrigeration machine that used vapor instead of liquid, and 1902 when Willis Haviland Carrier demonstrated the first air conditioner, scores of inventors contributed many small advances in cooling machinery. Oliver Evans ( 13 September, 1755 &ndash 15 April, 1819) was a United States Inventor. Willis Haviland Carrier ( November 26, 1876 – October 7, 1950) was an Engineer and Inventor, and is known as the An air conditioner is an Appliance, System, or mechanism designed to extract Heat from an area via a Refrigeration cycle In 1850 or 1851, Dr. John Gorrie demonstrated an ice maker. John Gorrie, ( October 3, 1802 &ndash June 29, 1855) physician scientist inventor and humanitarian is considered the father of In 1857, Australian James Harrison introduced vapor-compression refrigeration to the brewing and meat packing industries. James Harrison may refer to James Harrison (priest (died 1602 James Harrison (justice (fl The absorption refrigerator was invented by Baltzar von Platen and Carl Munters in 1922, while they were still students at the Royal Institute of Technology in Stockholm, Sweden. Baltzar von Platen can refer to Baltzar von Platen (1766-1829 Swedish naval officer and statesman Baltzar von Platen (1804-1875, Swedish The Royal Institute of Technology or Kungliga Tekniska högskolan ( KTH) is a University in Stockholm, Sweden. ('stɔkhɔlm is Sweden 's Capital and its largest City. It is the site of the national Swedish government, the parliament, and the It became a worldwide success and was commercialized by Electrolux. Other pioneers included Charles Tellier, David Boyle, and Raoul Pictet. Charles Tellier (1828-1913 was a French engineer born in Paris. David Boyle may refer to David Boyle 1st Earl of Glasgow (166-1733 Scottish nobleman David Boyle (author, economics author and journalist Raoul-Pierre Pictet ( 4 April 1846 &ndash 27 July 1929) was a Swiss Physicist and the first person to liquefy nitrogen

A Monitor-style (General Electric format) refrigerator, more like an icebox with its refrigerating mechanisms on top.

At the start of the 20th Century, about half of households in the United States relied on melting ice (and an icebox) to keep food cold, while the remaining half had no cooled storage at all. An Icebox was the common appliance for providing Refrigeration in the home before safe refrigerants made compact mechanical Refrigerators useful The ice used for household storage was expensive because ice had to be cut from winter ponds (or mechanically produced), stored centrally until needed, and delivered regularly.

In a few exceptional cases, mechanical refrigeration systems had been adapted by the start of the 20th century for use in the homes of the very wealthy, and might be used for cooling both living and food storage areas. One early system was installed at the mansion of Walter Pierce, an oil company executive. ^[2]

Marcel Audiffren of France championed the idea of a refrigerating machine for cooling and preserving foods at home. Marcel Audiffren, was a French priest physicist and inventor who promoted the residential Refrigerator. His U. S. patents, issued in 1895 and 1908, were purchased by the American Audiffren Refrigerating Machine Company. Machines based on Audiffren's sulfur dioxide process were manufactured by General Electric in Fort Wayne, Indiana and marketed by the Johns-Manville company. Fort Wayne is a City in northeastern Indiana, United States and the County seat of Allen Johns-Manville is an American corporation based in Denver Colorado[http //www The first unit was sold in 1911. Audiffren machines were expensive, selling for about $1,000 — about twice as much as an automobile cost at the time.

General Electric sought to develop refrigerators of its own, and in 1915 the first Guardian unit was assembled in a back yard wash house as a predecessor to the Frigidaire. Frigidaire is a major US Appliance company owned by Electrolux. In 1916 Kelvinator and Servel came out with two units among a field of competing models. This number increased to 200 by 1920. In 1918, Kelvinator had a model with automatic controls.

These home units usually required the installation of the mechanical parts, motor and compressor, in the basement or an adjacent room while the cold box was located in the kitchen. There was a 1922 model that consisted of a wooden cold box, water-cooled compressor, an ice cube tray and a 9 cubic foot compartment for $714. Water cooling is a method of Heat removal from components As opposed to Air cooling, Water is used as the heat transmitter O'Shea Jackson (born June 15 1969 better known by his Stage name Ice Cube, is an American Actor, Screenwriter, producer, and The cubic foot is an imperial and US customary (non- metric) unit of Volume, used in the United States Canada and the United Kingdom (A 1922 Model-T Ford cost about $450. The Ford Model T (colloquially known as the Tin Lizzie and also the Flivver) was an Automobile produced by Henry Ford 's Ford ) In 1923 Frigidaire introduced the first self-contained unit. About this same time porcelain covered metal cabinets began to appear. Ice cube trays were introduced more and more during the 1920s; up to this time freezing was not a function of the modern refrigerator.

The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927. A monitor was a type of relatively small Warship which was neither fast nor strongly armoured but carried disproportionately large guns and was used by some navies The compressor assembly, which emitted a substantial amount of heat, was placed above the cabinet, and surrounded with a decorative ring. Over 1,000,000 units were produced. These refrigerators used either sulfur dioxide or methyl formate as a refrigerant. Methyl formate, also called methyl methanoate, is the methyl Ester of Formic acid. Many units are still functional today.

Older U. S. refrigerator model, with freezer compartment

The introduction of freon expanded the refrigerator market during the 1930s, and freezer units became a little more common and requested during the 1940s. Freon is DuPont 's trade name for its odorless colorless nonflammable and noncorrosive Chlorofluorocarbon and Hydrochlorofluorocarbon Refrigerants Home units did not go into mass production until after WWII. The 1950s and 1960s saw technical advances like automatic defrosting and automatic ice making. Defrosting is a procedure performed periodically on Refrigerators and Freezers to maintain their operating efficiency Developments of the 1970s and 80s brought about more efficient refrigerators, and environmental issues banned the use of CFC (freon) refrigerants used in sealed systems.

Early refrigerator models (1916 and on) featured a cold compartment for ice cube trays. Successful processing of fresh vegetables through freezing began in the late 1920s by the Postum Company (the forerunner of General Foods) which had acquired the technology when it bought the rights to Clarence Birdseye’s successful fresh freezing methods. General Foods Corporation was a company whose direct predecessor was established in the USA by Charles William Post ( October 26, 1854 - Clarence Frank Birdseye II ( December 9, 1886 - October 7, 1956) was an American Inventor who is considered the founder

The first successful example of the benefits of frozen foods occurred when General Foods heiress Marjorie Merriweather Post (then wife of Joseph E. Davies, United States Ambassador to the Soviet Union ) deployed commercial grade freezers to Spasso House (US Embassy) in Moscow in advance of the Davies’ arrival. Marjorie Merriweather Post aka Marjorie Merriweather Post Close Hutton Davies May ( March 15 1887 – September 12 1973) was a leading Joseph Edward Davies ( November 29[[ 876]]- May 9[[ 958]] was the second Ambassador to represent the United States in the Soviet Union The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 Moscow (Москва́ romanised: Moskvá, IPA: see also other names) is the Capital and the largest city of Post, fearful of the food processing safety observed in the USSR, then fully stocked the freezers with product processed from General Foods Birdseye unit. The frozen food stores allowed the Davies’ to lavishly entertain and serve fresh frozen foods that would otherwise be out of season. Upon returning from Moscow, Post (who resumed her maiden name after divorcing Davies) directed General Foods to market frozen product to upscale restaurants.

Introduction of home freezer units occurred in the United States in 1940, and frozen foods began to make the transition from luxury to necessity.

Energy Efficiency

A frost-free units uses a blower fan to keep moisture out of the unit. It also has a heating coil beneath the evaporator that periodically heats the freezer compartment and melts any ice buildup. Some units also have heaters in the side of the door to keep the unit from "weeping. " Manual defrost units are available in used-appliance shops or by special order.

Refrigerators used to consume more energy than any other home appliance, but in the last twenty years great strides have been made to make refrigerators more energy efficient. In the early 90s a competition was held among the major manufacturers to encourage energy efficiency. Current models that are Energy Star qualified use 50 percent less energy than models made before 1993. Energy Star is an international standard for energy efficient Consumer products ^[3] The most energy-efficient unit made in the US is designed to run on 12 or 110 volts, and consumes about half a kilowatt-hour per day. [1] But even ordinary units are quite efficient; some smaller units use little more than one kilowatt-hour per day. Larger units, especially those with large freezers and icemakers, may use as much as 4 kwh per day.

How a refrigerator works

Main article: Refrigeration

Refrigerators work by the use of heat pumps operating in a refrigeration cycle. Refrigeration is the process of removing Heat from an enclosed space or from a substance and moving it to a place where it is unobjectionable A heat pump is a machine or device that moves Heat from one location (the 'source' to another location (the 'sink' or 'heat sink' using work. An industrial refrigerator is simply a refrigerator used in an industrial setting, usually in a restaurant or supermarket. They may consist of either a cooling compartment only (a larger refrigerator) or a freezing compartment only (a freezer) or contain both. The industry has nicknames for these units as well sometimes referring to them as a “cold box” or a “walk-in. ” The dual compartment was introduced commercially by General Electric in 1939.

The vapor compression cycle is used in most household refrigerators. In this cycle, a circulating refrigerant such as R134a enters the compressor as a vapor at its boiling point. A refrigerant is a compound used in a heat cycle that undergoes a Phase change from a Gas to a Liquid and back The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid The vapor is compressed and exits the compressor as a superheated vapor. The superheated vapor travels through part of the condenser which removes the superheat by cooling the vapor. The vapor travels through the remainder of the condenser and is condensed into a liquid at its boiling point. The saturated liquid refrigerant passes through the expansion valve where its pressure abruptly decreases. The decrease in pressure results in the flash evaporation and auto-refrigeration of a portion of the liquid (typically, less than half of the liquid flashes). The cold and partially vaporized refrigerant travels through the coil or tubes in the evaporator. There, a fan circulates room air across the coil or tubes, and the refrigerant is totally vaporized, extracting heat from the air which is then returned to the food compartment. The refrigerant vapor returns to the compressor inlet to complete the thermodynamic cycle. A thermodynamic cycle is a series of Thermodynamic processes which returns a system to its initial state

An absorption refrigerator works differently from a compressor refrigerator, using a source of heat, and typically runs more quietly. The absorption refrigerator is a Refrigerator that utilizes a heat source (e In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature

The Peltier effect uses electricity directly to pump heat; refrigerators using this effect are sometimes used for camping, or where noise is not acceptable. The thermoelectric effect is the direct conversion of temperature differences to electric Voltage and vice versa They are totally silent, but less energy-efficient than other methods.

Other alternatives to the vapor-compression cycle but not in current use include thermionic, vortex tube, air cycle, magnetic cooling, Stirling cycle, Malone refrigeration, acoustic cooling, pulse tube and water cycle systems. For the term 'vortex-tube' used in Fluid dynamics please see Vorticity The vortex tube, also known as the Ranque-Hilsch vortex A Stirling engine is a closed-cycle regenerative Heat engine with a Gaseous working fluid ^[4]

Types of domestic refrigerators

Household refrigerator output in 2000

Domestic refrigerators and freezers for food storage are made in a range of sizes. Amongst the smallest is a 4 L Peltier fridge advertised as being able to hold 6 cans of beer. Beer is the world's oldest and most widely consumed Alcoholic beverage and the third most popular drink overall after water and tea A large domestic fridge stands as tall as a person and may be about 1 m wide with a capacity of 600 L. Some models for small households fit under kitchen work surfaces, usually about 86 cm high. The household is the basic unit of analysis in many Social, Microeconomic and Government models Fridges may be combined with freezers, either stacked with fridge or freezer above, below, or side by side. A fridge without a true freezer may have a small compartment to make ice. Freezers may have drawers to store food in, or they may have no divisions (chest freezers).

Fridges and freezers may be free-standing, or built into a kitchen.

Compressor refrigerators are by far the most common type; they make a noticeable noise. Absorption or Peltier units are used where quiet running is required; Peltier coolers are used in the smallest refrigerators as they have no bulky mechanism.

Compressor and Peltier refrigerators are invariably powered by electricity; absorption units can in principle be designed to be powered by any heat source. Gas-only and dual power gas/electricity units are available.

Refrigeration units for commercial and for non-food use are made in a huge range of sizes and styles.

Many Koreans store kimchi in a kimchi refrigerator (hangul: 김치냉장고) that is specifically designed with precise controls to keep different varieties of kimchi at optimal temperatures for various stages of fermentation and also for longer storage than in regular refrigerators. The Korean people are an East Asian Ethnic group. Most Koreans speak the Korean language. Kimchi, also spelled gimchi or kimchee, is a traditional Korean fermented dish made of vegetables with varied seasonings most commonly referring to Kimchi Refrigerator is a storage-specific Refrigerator for Kimchi only

Impact on lifestyle

The invention of the refrigerator has allowed the modern family to purchase, store, freeze, prepare and preserve food products in a fresh state for much longer periods of time than was previously possible. For the majority of families without a sizeable garden in which to grow vegetables and raise livestock, the advent of the refrigerator along with the modern supermarket led to a vastly more varied diet and improved health resulting from improved nutrition. Customer divider barjpg|thumb|In supermarkets sellers periodically change prices for classes of goods in response to market conditions rather than negotiating the price of each good Nutrition (also called nourishment or aliment) is the provision to cells and Organisms of the materials necessary (in the form of food to support Dairy products, meats, fish, poultry and vegetables can all be kept refrigerated in the same space within the kitchen (although raw meat should be kept separate from other foodstuffs for reasons of hygiene). Dairy products are generally defined as Foodstuffs produced from Milk. In modern English usage meat most often refers to Animal tissue used as food mostly Skeletal muscle and associated Fat, but it may also refer Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Poultry is the category of Domesticated Birds which some humans keep for the purpose of collecting their eggs, or kill for their Meat and/or The term " vegetable " generally means the edible parts of Plants The definition of the word is traditional rather than Scientific, however Hygiene refers to practices associated with ensuring good health and cleanliness

The refrigerator allows families to consume more salads, fresh fruits and vegetables during meals without having to own a garden or an orchard. Exotic foodstuffs from far-off countries that have been imported by means of refrigeration can be enjoyed in the home because of the availability of domestic refrigeration.

The luxury of freezing allows households to purchase more foods in bulk that can be eaten at leisure while the bulk purchase provides cost savings (see economies of scale). Ice cream, a popular commodity of the 20th century, was previously only available by traveling long distances to where the product was made fresh and had to be eaten on the spot. Ice cream or ice-cream (originally iced cream) is a frozen dessert made from Dairy products such as Milk and Cream, combined Now it is a practically ubiquitous food item. Ice on-demand not only adds to the enjoyment of cold drinks, but is useful in first-aid applications, not to mention cold packs that can be kept frozen for picnics or in case of emergency. First aid is the provision of initial care for an Illness or Injury.

Features

The inside of a common U. S. home refrigerator

Newer refrigerators may include:

• Frost-free refrigeration;
• A power failure warning, alerting the user by flashing a temperature display. Certain Bibcocks (sillcocks are also known as frost frees. A frost free (also called Auto-defrost or no-frost Refrigerator The maximum temperature reached during the power failure may be displayed, along with information on whether the frozen food has defrosted or may contain harmful bacteria;
• Chilled water and ice available from an in-door station, so the door need not be opened;
• Cabinet rollers that allow the refigerator to be easily rolled around for easier cleaning;
• Adjustable shelves and trays that can be moved around to suit the user;
• A Status Indicator to notify the user when it is time to change the water filter;
• An in-door ice caddy, which relocates the ice-maker storage to the freezer door and saves approximately 60 litres (about 2 cubic feet) of usable freezer space. It is also removable, and helps to prevent ice-maker clogging;
• A cooling zone in the refrigerator door shelves. Air from the freezer section is diverted to the refrigerator door, to better cool milk or juice stored in the door shelf;

• Extras unrelated to refrigeration, such as a television set, radio, or DVD player built into a door. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. This page relates to a Hardware device used to play DVDs For the Apple Software program, see DVD Player (Apple.

• Automatic ice makers/water coolers. Some even have dispensers allowing dispensing without opening the door.

Early freezer units accumulated ice crystals around the freezing units. Ice crystals - small crystalline form of Ice including hexagonal columns hexagonal plates dendritic crystals and Diamond dust. This was a result of humidity introduced into the units when the doors to the freezer were opened. This build up of frost required periodic thawing of the units to maintain their efficiency. Advances in frost-free refrigeration eliminating the thawing task were introduced in the 1950s. Also, early units featured freezer compartments located within the larger refrigerator, and accessed by opening the refrigerator door, and then the smaller internal freezer door; units featuring entirely separate freezer compartment were introduced in the early 1960s, becoming the industry standard by the middle of that decade.

Later advances included automatic ice units and self compartmentalized freezing units.

An increasingly important environmental concern is the disposal of old refrigerators - initially because of the freon coolant damaging the ozone layer, but as the older generation of refrigerators disappears it is the destruction of CFC-bearing insulation which causes concern. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 Modern refrigerators usually use a refrigerant called HFC-134a (1,2,2,2-tetrafluoroethane), which has no ozone layer depleting properties, instead of freon.

Disposal of discarded refrigerators is regulated, often mandating the removal of doors: children playing hide-and-seek have been asphyxiated while hiding inside a discarded refrigerator. This was particularly true for the older models that had latching doors. More modern units use a magnetic door gasket to hold the door sealed but can actually be pushed open from the inside. However, children can be unwittingly harmed by hiding inside any discarded refrigerator. ^[5]

Temperature zones and ratings

Commercial for electric refrigerators in Pittsburgh, USA, 1926

Some refrigerators are now divided into four zones to store different types of food:

• -18 °C (0 °F) (freezer)
• 0 °C (32 °F) (meats)
• 5 °C (40 °F) (refrigerator)
• 10 °C (50 °F) (vegetables)

The capacity of a refrigerator is measured in either litres or cubic feet (US). Typically the volume of a combined fridge-freezer is split to 100 litres (3. 53 cubic feet) for the freezer and 140 litres (4. 94 cubic feet) for the refrigerator, although these values are highly variable.

Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers (for example, 1 through 9, warmest to coldest) by manufacturers, but generally 2 to 8 °C (36 to 46 °F) is ideal for the refrigerator compartment and -18 °C (0 °F) for the freezer. Some refrigerators require a certain external temperature (60 °F) to run properly. This can be an issue when placing a refrigerator in an unfinished area such as a garage.

European freezers, and refrigerators with a freezer compartment, have a four star rating system to grade freezers. Stars are often used as symbols for classification purposes They are used by reviewers for ranking things such as movies TV shows restaurants and hotels

• *  : max temperature = -6°C. The Celsius Temperature scale was previously known as the centigrade scale. Maximum storage time for frozen food is 1 week
• **  : max temperature = -12°C. Maximum storage time for frozen food is 1 month
• ***  : max temperature = -18°C. Maximum storage time for frozen food is 3 months
• *(***) : max temperature = -18°C. Maximum storage time for frozen food is up to 12 months

Although both the three and four star ratings specify the same maximum temperature of -18°C, only a four star freezer is intended to be used for freezing fresh food. Three (or fewer) stars are used for frozen food compartments which are only suitable for storing frozen food; introducing fresh food into such a compartment is likely to result in unacceptable temperature rises.

See also

• Energy Star
• Star rating
• Thermoacoustic refrigeration
• Thermoelectric cooling

Notes and references

External links

• Refrigeration History
• The History of the Refrigerator and Freezers
• How does a gas-powered fridge actually work (without compressor - using heater to power the heat transfer cycle) Archived Page
• Elert, Glenn. Refrigerators. The Physics Hypertextbook.
• How Refrigerators Work Article by HowStuffWorks
• Refrigerators, Canada Science and Technology Museum
• How Refrigerators Work and What goes wrong with them Article by Apwagner. The Canada Science and Technology Museum ( Musée des sciences et de la technologie du Canada) is located in Ottawa, Ontario, Canada on St com