Refrigerator

A typical refrigerator with its door open

A refrigerator is a cooling apparatus. The common household appliance (often called a "fridge" for short) comprises a thermally insulated compartment and a heat pump—chemical or mechanical means—to transfer heat from it to the external environment (i.e., the room in which it is located), cooling the contents to a temperature below ambient. Cooling is a popular food storage technique in developed countries and works by decreasing the reproduction rate of bacteria. The device is thus used to reduce the rate of spoilage of foodstuffs. A device described as a "refrigerator" maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F)[1]. A similar device which maintains a temperature below the freezing point of water is called a "freezer". The refrigerator is a relatively modern invention among kitchen appliances. It replaced the icebox, which had been a common household appliance for almost a century and a half prior. For this reason, a refrigerator is sometimes referred to as an "icebox".

Contents

Freezer

Freezer units are used in households and in industry and commerce. Most freezers operate around 0 °F (−18 °C). Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers are generally upright units resembling refrigerators, or chests resembling upright units laid on their side. Many upright modern freezers come with an ice dispenser built into their door.

Commercial and domestic refrigerators

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 gas systems, which occasionally leaked, 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. 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.[2]

Styles of Refrigerators

Most Americans still have the traditional freezer top and refrigerator on the bottom, this has been the basic style since the 1940s.

In the 1950s refrigerators were white, but in the 1960s through present designers and manufacturers put color into refrigerators. In the 1960s people had pink colors, in the 1970s colors were green, almond. In the 1980s, black colors were viewed as luxurious. In the late 1990s, stainless steel became stylish.

Also many refrigerators could be blended into the cabinetry of the kitchen with panels that could slide over the doors for a built-in look. This cost money, because the doors have to be modified.

Today's popular colors are:

Popular Styles:

The basic home refrigerator weighs 200-450 lbs, but the Sub Zero weighs 875 lbs and requires 4 delivery men to deliver the appliance. The cost of a refrigerator can cost between $400.00 for a basic type to $7,000 for a Sub Zero type.

History

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

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. Natural means are still used to cool foods today. On mountainsides, runoff from melting snow is a convenient way to cool drinks, and during the winter one can keep milk fresh much longer just by keeping it outdoors.

In the 11th century, the Persian physicist and chemist Ibn Sina (Avicenna) invented the refrigerated coil, which condenses aromatic vapours.[3][4] This was a breakthrough in distillation technology and he made use of it in his steam distillation process, which requires refrigerated tubing, to produce essential oils.[5]

The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow in 1748. Between 1805, when Oliver Evans designed the first refrigeration machine that used vapour 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-home refrigeration became a reality in 1834 with the invention of the cooling compression system by the American inventor Jacob Perkins.[6] In 1850 or 1851, Dr. John Gorrie demonstrated an ice maker.

In 1857, Australian James Harrison developed the world first practical ice making machine and refrigeration system, and it was used in the brewing and meat packing industries of Geelong, Victoria. Ferdinand Carré of France developed a somewhat more complex system in 1859. Unlike earlier compression-compression machines, which used air as a coolant, Carré's equipment contained rapidly expanding ammonia. 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. It became a worldwide success and was commercialized by Electrolux. Other pioneers included Charles Tellier, David Boyle, and Raoul Pictet. Carl von Linde was the first to patent and make a practical and compact refrigerator.

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 (0.25 m3) compartment, and cost $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 an auxiliary function of the modern refrigerator.

The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927, so-called because of its resemblance to the gun turret on the ironclad warship USS Monitor of the 1860s. The compressor assembly, which emitted a great deal of heat, was placed above the cabinet, and surrounded with a decorative ring. Over a million units were produced. As the refrigerating medium, these refrigerators used either sulfur dioxide, which is corrosive to the eyes and may cause loss of vision, painful skin burns and lesions, or methyl formate, which is highly flammable, harmful to the eyes, and toxic if inhaled or ingested. Many of these units are still functional today. These cooling systems cannot legally be recharged with the hazardous original refrigerants if they leak or break down.

The introduction of Freon in the 1920s expanded the refrigerator market during the 1930s and provided a safer, low-toxicity alternative to previously used refrigerants. Separate freezers became common during the 1940s, the popular term at the time for the unit was a "deep freeze". These devices, or "appliances", did not go into mass production for use in the home until after World War II. The 1950s and 1960s saw technical advances like automatic defrosting and automatic ice making. More efficient refrigerators were developed in the 1970s and 1980s, even though environmental issues led to the banning of very effective (Freon) refrigerants. Early refrigerator models (from 1916) had a cold compartment for ice cube trays. From the late 1920s fresh vegetables were successfully processed through freezing 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.

The first successful application 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 in Spaso House, the US Embassy in Moscow, in advance of the Davies’ arrival. Post, fearful of the USSR's food processing safety standards, fully stocked the freezers with products from General Foods' Birdseye unit. The frozen food stores allowed the Davies to entertain lavishly 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.

Home freezers as separate compartments (larger than necessary just for ice cubes), or as separate units, were introduced in the United States in 1940. Frozen foods, previously a luxury item, began to be commonplace.

General technical explanation

Main article: Refrigeration
Vapor Compression Cycle: 1) Condenser, 2) Expansion valve, 3) Evaporator unit, 4) Compressor
An Embraco compressor and fan-assisted condenser coil

A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as low-pressure vapor at or slightly above the temperature of the refrigerator interior. The vapor is compressed and exits the compressor as high-pressure superheated vapor. The superheated vapor travels under pressure through coils or tubes comprising "the condenser", which are passively cooled by exposure to air in the room. The condenser cools the vapor, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant is forced through a metering or throttling device, also known as an expansion valve (essentially a constriction) to an area of much lower pressure. The sudden decrease in pressure results in explosive-like flash evaporation of a portion (typically about half) of the liquid. The latent heat absorbed by this flash evaporation is drawn mostly from adjacent still-liquid refrigerant, a phenomenon known as "auto-refrigeration". This cold and partially vaporized refrigerant continues through the coils or tubes of the evaporator unit. A fan blows air from the refrigerator or freezer compartment ("box air") across these coils or tubes and the refrigerant completely vaporizes, drawing further latent heat from the box air. This cooled air is returned to the refrigerator or freezer compartment, and so keeps the box air cold. Note that the cool air in the refrigerator or freezer is still warmer than the refrigerant in the evaporator. Refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle.

An absorption refrigerator works differently from a compressor refrigerator, using a source of heat, such as combustion of liquefied petroleum gas, solar thermal energy or an electric heating element. These heat sources are much quieter than the compressor motor in a typical refrigerator. A fan or pump might be the only mechanical moving parts; reliance on convection is considered impractical.

The Peltier effect uses electricity to pump heat directly; this type of refrigerator is sometimes used for camping, or where noise is not acceptable. They can be totally silent (if they don't include a fan for air circulation) but are less energy-efficient than other methods.

Other uses of an absorption refrigerator (or "chiller") include large systems used in office buildings or complexes such as hospitals and universities. These large systems are used to chill a brine solution that is circulated through the building.

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.[7]

Features

The inside of a typical western home refrigerator

Newer refrigerators may include:

Water and Ice Dispensing became available in the 1970s. Also most refrigerators have icemakers built-in so the user doesn't have to use ice trays. Some refrigerators have water chillers and water filtration systems.

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 frost buildup required periodic thawing ("defrosting") of the units to maintain their efficiency. Manual Defrost (referred to as Cyclic) units are still available. Advances in automatic defrosting eliminating the thawing task were introduced in the 1950s, but are not universal, due to energy performance and cost. These units utilized a counter, that only defrosted the freezer compartment (Freezer Chest) when a specific number of door openings had been made. The units were just a small timer combined with an electrical heater wire which heated the freezer's walls for a short amount of time to remove all traces of frost/frosting. 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 an entirely separate freezer compartment were introduced in the early 1960s, becoming the industry standard by the middle of that decade. These older freezer compartments were the main cooling body of the refrigerator, and only maintained a temperature of around -6°C, which is suitable for keeping food for a week.

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 (1,1,1,2-Tetrafluoroethane), which does not deplete the ozone layer, 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 discarded refrigerators, particularly older models with latching doors. More modern units use a magnetic door gasket which holds the door sealed but can be pushed open from the inside. This gasket was invented by Herman C. Ells Sr. But children can still come to harm if they hide in a discarded refrigerator.[8]

Types of domestic refrigerators

Household refrigerator output in 2000

Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest is a 4 L Peltier fridge advertised as being able to hold 6 cans of beer. 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. Fridges may be combined with freezers, either stacked with fridge or freezer above, below, or side by side. A fridge without a frozen food storage compartment may have a small section just to make ice cubes. 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.

Energy efficiency

An auto-defrost unit 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 1990s 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.[12] The most energy-efficient unit made in the US is designed to run on 120 or 110 volts, and consumes about half a kilowatt-hour per day.[13] But even ordinary units are quite efficient; some smaller units use less than 0.5 kilowatt-hour per day. Larger units, especially those with large freezers and icemakers, may use as much as 4 kW·h per day.

Many older refrigerators can be made more efficient, with new door seals, thermostat, and insulation. A program in the eastern states of Australia called the 'Phoenix Fridge' refurbished older refrigerators (making them more efficient) and distributed them to low income families. This is a very good example of recycling

Among the different styles of refrigerators, top-freezer models are more efficient than bottom-freezer models of the same capacity, which are in turn more efficient than side-freezer models. Models with through-the-door ice units are less efficient than those without.[14] Dr. Tom Chalko in Australia has developed an external thermostat to convert any chest freezer into a chest fridge using only about 0.1kWh per day—the amount of energy used by a 100 watt light bulb in one hour.[15] A similar device is manufactured by Johnson Controls.[16] Scientists at Oxford University have reconstructed a refrigerator invented in 1930 by Leó Szilárd and Albert Einstein in their efforts to replace current technologies with energy efficient green technology. The Einstein refrigerator operates without electricity and uses no moving parts or greenhouse gases.[17]

Impact on lifestyle

The refrigerator allows the modern family to keep food fresh for much longer than before. This, along with the modern supermarket, allows most families, without a sizeable garden in which to grow vegetables and raise animals, a vastly more varied diet and improved health resulting from improved nutrition. Dairy products, meats, fish, poultry and vegetables can 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 lets people eat more salads, fresh fruits and vegetables, 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 domestic refrigeration.

Freezers allow households to buy food in bulk: it can be eaten at leisure, and bulk purchase saves money. Ice cream, a popular commodity of the 20th century, could previously only be obtained by traveling long distances to where the product was made fresh, and had to be eaten on the spot. Now it is a common food item. Ice on demand not only adds to the enjoyment of cold drinks, but is useful for first-aid, and for cold packs that can be kept frozen for picnics or in case of emergency.

Temperature zones and ratings

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

The capacity of a refrigerator is measured in either litres or cubic feet. 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 by manufacturers (for example, 1 through 9, warmest to coldest), but generally 3 to 5 °C (37 to 41 °F)[18] is ideal for the refrigerator compartment and −18 °C (−0 °F) for the freezer. Some refrigerators are required to be within certain external temperature parameters to run properly. This can be an issue when placing units 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.

Although both the three and four star ratings specify the same minimum 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. Most European Refrigerators include a Moist Cold Fridge section (which does require defrosting at irregular intervals) and a Frost Free Freezer section, to keep frozen food frost free.

Non-food use

Refrigerators have many other uses. Examples include laboratories, for storing samples awaiting analysis, and morgues, for storing corpses.

Recycling

Old refrigerators have been adapted to create low cost passive solar water heating systems.[19] Also, many refrigerators have been refurbished for low-income families in eastern Australia via the Phoenix fridge program (see energy efficiency)

See also

Notes and references

  1. ↑ http://www.bbc.co.uk/bloom/actions/fridgefreezertips.shtml
  2. ↑ Jstor.org: Household appliances and the use of time: the United States and Britain since the 1920s
  3. ↑ Pitman, Vicki (2004). Aromatherapy: A Practical Approach. Nelson Thornes. p. xi. ISBN 0748773460. 
  4. ↑ Myers, Richard (2003). The Basics of Chemistry. Greenwood Publishing Group. p. 14. ISBN 0313316643. 
  5. ↑ Marlene Ericksen (2000), Healing with Aromatherapy, p. 9, McGraw-Hill, ISBN 0658003828
  6. ↑ Who Invented the Refrigerator
  7. ↑ IIFIIR.org
  8. ↑ Adams, Cecil (2005). "Is it impossible to open a refrigerator door from the inside?". http://www.straightdope.com/columns/050304.html. Retrieved 2006-08-31. 
  9. ↑ Thermal mass refrigerators
  10. ↑ Solar refrigerators for developing world
  11. ↑ Magnetic refrigerators
  12. ↑ "Refrigerators & Freezers". Energy Star. http://www.energystar.gov/index.cfm?c=refrig.pr_refrigerators. 
  13. ↑ Humboldt.edu
  14. ↑ "What's more energy efficient, a refrigerator with a top-mounted freezers, bottom-mounted freezer, or a side-by-side?". Energy Star. http://energystar.custhelp.com/cgi-bin/energystar.cfg/php/enduser/std_adp.php?p_faqid=4912. 
  15. ↑ MTbest.net "A fridge that takes only 0.1 kWh a day?". http://mtbest.net/chest_fridge.pdf MTbest.net. 
  16. ↑ Kegman.net
  17. ↑ "Albert Einstein Refrigerator"
  18. ↑ http://www.bbc.co.uk/bloom/actions/fridgefreezertips.shtml
  19. ↑ "More ways to recycle old refrigerators into low cost solar water heaters". Mother Earth News. 1978 January. http://www.motherearthnews.com/Do-It-Yourself/1978-01-01/More-Ways-to-Recycle-Old-Refrigerators-into-Low-Cost-Solar-Water-Heaters.aspx. Retrieved 2009-10-13. 

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