Refrigerator

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"Fridge" redirects here. For other uses, see Fridge (disambiguation).

A refrigerator with its door open

A refrigerator (often called a "fridge" for short) is a cooling appliance for the storage and preservation of perishable food; food kept in a refrigerator lasts longer than that left at room temperature as the cold inhibits bacterial growth. A refrigerator maintains a cold temperature above the freezing point of water; commonly refrigerators are used in conjunction with freezers, which maintain temperatures below freezing, or a refrigerator may have an integrated freezer compartment. The refrigerator is a relatively modern invention amongst kitchen appliances. It replaced the common icebox which had been a household item for almost a century and a half prior, and is sometimes still called by the name "icebox".

Commercial units, which go by many other names, were in use for almost 40 years prior to the common home models. The fact that they operated with toxic ammonia gas systems made them unsafe for home use. Practical household refrigerators were introduced in the 1920s and gained wider acceptance in the 1930s as prices fell and non-toxic, nonflammable synthetic refrigerants, such as Freon or R-12 refrigerants were introduced.

1 History of development
2 The impact of the refrigerator on the home
3 How a refrigerator works
4 Types
5 Features
6 Fridge alternatives
7 Media
8 References
9 See also
10 External links

[edit] History of development

See also: Timeline of low-temperature technology

The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in the mid 1700s, and relied on the vapor-compression refrigeration process explained by Michael Faraday. 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. In 1850 or 1851, Dr. John Gorrie demonstrated an ice maker. In 1856, James Harrison introduced vapor-compression refrigeration to the brewing and meat packing industries. Other pioneers included Charles Tellier, David Boyle, and Raoul Pictet.

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. 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.^[1]

Marcel Audiffren of France championed the idea of a refrigerating machine for cooling and preserving foods at home, and he received U.S. Patents #551,107 (in 1895) and #898,400 (in 1908, with Albert Sigrun). These patents 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. The first unit was sold in 1911. Audiffren machines were expensive, selling for about $1,000 — about twice as much as an automobile.

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. 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. (A 1922 Model-T Ford cost about $450.) 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.

A monitor style (GE format) refrigerator, more like an icebox with its refrigerating mechanisms on top.

The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927. The compressor assembly, which emitted substantial amount of heat, was placed above the cabinet, and surrounded with a decorative ring. Over 1,000,000 units were produced. This refrigerator used sulfur dioxide refrigerant. Many units are still functional today.

The introduction of freon expanded the refrigerator market during the 1930s, and freezer units became a little more common and requested during the 1940s. Home units did not go into mass production until after WWII. The 1950s and 60s saw technical advances like automatic defrosting and automatic ice making. 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.

[edit] The impact of the refrigerator on the home

Virtually all homes in the developed world have a refrigerator of one kind or another. 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. 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).

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 due to 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. 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.

[edit] How a refrigerator works

Main article: refrigeration

Refrigerators work by the use of heat pumps operating in a refrigeration cycle. 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 freon enters the compressor as a vapor at its boiling point. 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 (also called a throttle 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 vapour returns to the compressor inlet to complete the thermodynamic cycle.

An absorption refrigerator works differently from a compressor refrigerator, and typically runs more quietly.

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

-18 °C (0 °F) (freezer)
0 °C (32 °F) (meats)
4 °C (40 °F) (refrigerator)
10 °C (50 °F) (vegetables)

The capacity of a refrigerator is measured in either liters (EUR) or cubic feet (US). Typically the freezer volume is 100 liters (3.53 cubic feet) and the refrigerator 140 liters (4.94 cubic feet), 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.

[edit] Types

Freestanding;
Counter/cabinet depth: a refrigerator can be approximately 75 cm (30 inches) deep as opposed to approximately 90 cm (35 inches) deep like a normal refrigerator. This allows the unit to be more flush with surrounding cabinets. A counter depth refrigerator tends to come at a steep price premium despite providing less capacity;
Built under: refrigerators and freezers which can be installed under the counter top. Often known as a Bar Fridge, it is used in personal bars as a means to cool beverages;
In-Column refrigerators or freezers: the appliance is built into a tall cabinet in the kitchen so that it looks like a normal cupboard.
A "Mini fridge" or a "micro-fridge" (with an attached compact microwave oven) for use in a college dormitory or efficiency apartment.

[edit] Features

The inside of a refrigerator

Newer refrigerators may include:

Automatic defrosting: In any refrigerator, over time, water vapor in the air condenses onto the cooling coils as frost, eventually building up into a thick layer of ice. This ice acts as an insulator, reducing cooling efficiency. In the past, the ice was removed by periodically emptying the refrigerator and turning it off to let the ice melt, perhaps aided by hot water applied by the user. In a refrigerator equipped for frost-free operation, however, a heater and a thermostat are fitted around the cooling coils. The cooling is periodically switched off (with the period varying between every 6 to 24 hours depending on the model) and the heater is turned on until the temperature around the coils slightly exceeds the freezing point of water, after which normal cooling resumes. This melts any frost which has collected around the coils and prevents ice from building up. Melt water typically drains into a tray at the bottom of the refrigerator from which it is then evaporated by the air flow across the condenser coil.
A power failure warning, alerting the user by flashing a temperature display. 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;
A Status Indicator to notify the user when it is time 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;
An LCD suggesting what types of food should be stored at what temperatures, and the expiration date of the food stored;
Extras unrelated to refrigeration, such as a television set built into a door.

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. Modern refrigerators usually use a refrigerant called HFC-134a (1,2,2,2-tetrafluoroethane) instead of freon, which has no ozone layer depleting properties.

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.^[2]

[edit] Fridge alternatives

Before the invention of the refrigerator, icehouses were used to provide cool storage for most of the year. 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.

[edit] Media

1953 Philco refrigerator ad. Note freezer compartment located within larger refrigerator unit. Units with completely-separate freezer compartments did not become the standard until the mid 1960s.

Theater commercial, electric refrigerator, 1926 (file info)
- Largely graphic commercial for electric refrigerators in general and a refrigerator show, presumably in Pittsburgh, in particular. (7.61 MB, ogg/Theora format).
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