Refrigerator

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

“Freezer” redirects here. For machine used to make ice cream, see Ice cream freezer.

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. 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 original name "icebox".

The word freezer is generally used to describe an appliance that keeps foods frozen. Freezers are common as household units for storing food but are also used in commercial settings. Most freezers operate around -18 °C (0 °F). Domestic freezers can be included as a compartment in a refrigerator 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.

Commercial fridge and freezer 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 were introduced.

1 How a refrigerator works
2 Types
3 Features
4 Temperature zones and ratings
5 Media
6 References
7 See also
8 External links

[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 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.

[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 common home 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 (a process known as defrosting). 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. Melt water drops into a small gulley, through a small pipe which drains into a tray on the top of the compressor from which it is then evaporated into the surrounding air by residual heat generated by the operation of the compressor.^[1]
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 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;
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.

Early freezer units accumulated ice crystals around the freezing units. 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 interal 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. 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]

Refrigerators may contain drawers known as 'crispers'. These drawers work primarily by providing less humidity and more humidity.

[edit] Temperature zones and ratings

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.

* : max temperature = -6°C. 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.

[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) — Watch in browser
- 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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