Refrigerator

A refrigerator (often called a "fridge" for short) is a mechanical appliance for the storage and preservation of perishable food. The term refrigerator is most commonly applied to the appliance used in the home. It is basically designed as a freezing unit with a compartment referred to as a freezer which shares its refrigeration with another compartment for cold temperatures maintained above freezing. The refrigerator is a relatively modern invention along side of most other kitchen appliances. It replaced the common icebox which had been a household item for almost a century and a half prior, and sometimes is still called by the name "icebox".

Commercial refrigeration 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.

History of development

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 process explained by Michael Faraday. Between the year 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 demonsrated 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. (see the article on refrigeration.)

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 it had to be cut from winter ponds (or mechanically produced), stored centrally until needed, and delivered regularly. (see the article on icebox.)

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 sulphur 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 about a 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 1920’s, 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. 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 1930’s, and freezer units became a little more common and requested during the 1940’s. Home units didn’t go into mass production until after WWII. The 1950’s and 60’s saw technical advances like automatic defrosting and automatic ice making. Developments of the 1970’s and 80’s brought about more efficient refrigerators, and environmental issues banned the use of CFC (freon) refrigerants used in sealed systems.

The impact of the refrigerator on the home

The refrigerator is the most used appliance in the home today. Yet it goes as the unsung invention of the 20th century. It even gains little respect by still being referred to as an “icebox,” but it has gained endearment by being called a “fridge.”

The refrigerator has allowed the modern family to purchase, store, freeze, prepare and preserve food products not generally found available in the natural locale. The reduction of the family garden for fresh produce has been replaced by the grocery store where multiple products can be purchased well ahead of time and retained in the home for future use. Dairy products, meats, fish, and poultry can all be kept refrigerated in the same space within the kitchen.

The refrigerator allows families to consume more salads, fresh fruits and vegetables during meals without having to own a garden or an orchard. Foods from other lands that have been imported by means of refrigeration can be enjoyed in the home due to the capability of in-home 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. Ice cream, a popular commodity of the 20th century, was 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 freezer luxury. Ice on-call 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 in case of emergency.

How it works

Refrigerators work by the use of phase change 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.

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 litres (EUR) or cubic feet (US). Typically the freezer volume is 100 litres (3.53 cubic feet) and the refrigerator 140 litres (4.94 cubic feet), although these values are highly variable.

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.
Integrated.
In-Column refrigerators or freezers: these are built into a tall cabinet in your kitchen furniture. The appliance is built in to your kitchen so that it looks like a normal cupboard. Getting the right size refrigerator is very important when choosing integrated.

Door configuration

Eye level freezer refrigerator (or top mount).
Bottom freezer refrigerator (or bottom mount). The freezer is generally bigger and the refrigerator has two independent motor-compressor units.
French door (or trio). Similar to bottom freezer, but the refrigerator (top) section has two doors that swing outward like a kitchen pantry.
Side-by-side. The unit is divided into two tall compartments, with the freezer on the left and the refrigerator on the right.
Wide-by-side. Similar to side-by-side, but the refrigerator compartment is wider at eye level and becomes narrow at the bottom. Allows the convenience of a side-by-side, but able to fit wider items in the refrigerator. Made popular by Maytag.
Single door. Originally, most units featured only one door, with the freezer compartment located within the larger refrigerator compartment. Beginning in the early 1960s manufacturers began offering units with separate freezer compartments, which gradually took over the market. One-door models, though still manufactured, are now rare in full size. This style is still common with small half-size refrigerators.

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Features

Some newer refrigerators may feature:

An in-door ice caddie, 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. In-door ice caddies are exclusive to side-by-side refrigerators.
Frost-free operation. Over time atmospheric water vapor condenses onto the cooling coils as ice, which can eventually build up into a layer several centimetres thick. This can be removed by emptying the refrigerator and turning it off so that the ice melts. In a refrigerator equipped for frost-free operation, a heater and a thermostat are fitted around the cooling coils. The cooling is periodically switched off (varies between every 6 to 24 hours depending on model) and the heater turned on until the temperature around the coils slightly exceeds the freezing point of water, after which normal cooling is resumed. This melts any ice which has collected around the coils and prevents it from building up.
A cooling zone in the refrigerator door shelves. Air from the freezer section is diverted to the refrigerator door, helping to keep milk or juice in the door shelf colder.
An LCD suggesting what types of food should be stored at what temperatures and the expiration date of the food stored.
A power failure warning, alerting the user to the failure, usually by flashing the 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.
Filter Status Indicator tells user when it's time for a change.
Extras unrelated to refrigeration, such as a television set built into a door, with cable and A/V hookups behind the fridge.

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 very often strictly regulated by municipalities, by mandating the removal of doors, as many children playing hide-and-seek have been asphyxiated while hiding inside a discarded refrigerator.

File:53Philco.jpg

1953 Philco refrigerator ad. Note freezer compartment located within larger refrigerator unit.

Microwave-refrigerator combo

A microwave/refrigerator combo is a freezer, refrigerator and microwave oven combined into a single, compact, energy-efficient unit. The foods can be transferred from one compartment to the other one following a timer to defrost, warm and cook them (with a week program, if necessary). [edit]

Refrigerator Temperature Settings

Temperature settings for refrigerator and freezer compartments are given arbitrary numbers for example (1 through 9, warmest to coldest) by manufacturers, but generally 3 °C (37 °F) is ideal for the refrigerator compartment and -18 °C (0 °F) for the freezer. If you suspect a problem, test the temperatures with a refrigerator or outdoor thermometer.

See Heat pump and Phase change heat pump

Media

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External links

History of the Refrigerator - Gizmohighway Technology Guide
How Refrigerators Work Article by HowStuffWorks
The History of the Refrigerator and Freezers
The History of Sub-Zero Article by Sub-Zero on the History of the Refrigerator
How does a gas-powered fridge actually work (without compressor - using heater to power the heat transfer cycle)