Refrigerators and Freezers
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Wikipedia-Article "Refrigerators"
Refrigeration (from the Latin frigus, frost) is generally the cooling of a body by the transfer of a portion of its heat away from it. Applications include conservation, especially of food, and lowering the temperature of drinks to one that is more agreeable for consumption. Domestic refrigerators are common in kitchens, with separate sections or separate machines for cooling and freezing.
Cooling of something hot is often done by means of material at ambient temperature, for example the fan cooling of computer equipment.
Where temperatures below that of any available natural cooling agent are required, refrigerators are used to produce the required cooling effect by taking in heat at low temperatures and rejecting it at temperatures somewhat above that of the natural cooling agent, which is generally water or air. The function of a refrigerating machine, therefore, is to take in heat at a low temperature and reject it at a higher one, using external energy to drive the process. A refrigerator is effectively a heat pump, a heat engine running in reverse. It is also possible to use eutectic salts.
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Thermodynamics of refrigerators
Most home and automotive refrigerators qualify as phase change heat pumps. They convert a refrigerant from gas to liquid and back again by compression in a refrigeration cycle. In principle, any endothermic process could be used provided it is balanced by an exothermic in another physical location so that it can operate in a cycle. For example, absorption of gaseous ammonia into water is used in most gas absorption refrigerators, and the Einstein refrigerator is a version of this which contains no moving parts — the cooling effect in this case coming from the heat absorbed by the ammonia when it evaporates from the water.
Other processes which have been used on a small scale include the Peltier effect for thermoelectric cooling.
History of refrigeration
- Ice houses
- Making of ice cream
- Refrigeration by well water
Development of the first refrigerators
Many countries can claim to be the home of the inventor of the refrigerator, as the technology was developed over a period of time all over the world using different types of technology and for different purposes. Claimants to the name of inventor include Oliver Evans (USA), Jacob Perkins (USA and England), John Gorrie (USA), Alexander Catlin Twining (USA), James Harrison and Thomas Mort (Australia) and Carl von Linde (Germany). One of the first uses of "home" refrigeration was at Biltmore Estate in Asheville, North Carolina, USA, installed around 1895 [1], while in commercial refrigeration the Vestey Brothers opened one of the first refrigerated cold stores in London the same year.
The gas absorption refrigerator, which cools by the use of a source of heat, was invented in Sweden by Baltzar von Platen in 1922. [2] It was later manufactured by Electrolux and Servel. Today it is used in homes that are not connected to the electrical grid, and in recreational vehicles.
Technology
- Chlorofluorocarbons (CFCs) (Freon)
- Liquefied gases
- Heat pump
- Heat pipe
- Thermoelectric cooling
- Sonic refrigeration
- Magnetic refrigeration
Culture and commerce
Refrigerated trucks (or simply refrigerators) are used to transport perishable goods, such as, for instance, frozen foods, fruit and vegetables, and temperature-sensitive chemicals. Most modern refrigerators keep temperature -40...+20 °C and have a maximum payload of around 24 000 kg. gross weight (in Europe). Surprisingly, refrigerated trucks are most wanted in winter, when there is a significant demand to transport chemicals under relatively high (+10...+20 °C) temperature.
- Food hygiene
- Ready meals
- Cook/chill
- Ice cream vans
- Air conditioning
- HVAC
Science
- approaching absolute zero
- Cryogenics and cryocoolers
- Superconductivity
- Superfluidity
Speculative uses of refrigeration
See also
- Refrigerant
- Einstein refrigerator
- Free cooling
- Heat pump
- Home appliances : Domestic refrigerator
- Icyball
- Refrigerator car
- Thermodynamics
- Timeline of low-temperature technology
- James Harrison (1816 - 1893) Australian pioneer in the field of mechanical refrigeration.
- Zeer pot
External links
Wikipedia-Article "Freezers"
A refrigerator (often shortened to fridge) is an electrical appliance that uses refrigeration to help preserve food. A domestic refrigerator is present in 99.5% of American homes. It works using 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 dual compartment was introduced commercially by General Electric in 1939. Some refrigerators are now divided into four zones for the storage of 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 litres (or cubic feet). Typically the freezer volume is 100 litres (this will vary) and the refrigerator 140 litres.
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Types
- Freestanding
- Counter/cabinet depth: a refrigerator can be approximately 30 inches deep as opposed to approximately 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 alcholic 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 situation
- 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-compressors.
- 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 manufactuers began offering units with separate freezer compartments, which gradually took over the market. One-door models, though still manufactured, are now rare.
Features
Some newer refrigerators may feature:
- An LCD suggesting what types of food should be stored at what temperatures and the expiration date of the food stored.
- Filter Status Indicator tells you when it's time for a change.
- An in-door ice caddie, which relocates the icemaker storage to the freezer door and saves approximately 2 cubic feet (60 L) of usable freezer space. It is also removable, and helps to prevent icemaker clogging. In-door ice caddies are exclusive to side-by-side refrigerators.
- 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.
- 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.
- 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.
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.
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 transfered from one compartment to the other one following a timer to defrost, warm and cook them (with a week program, if necessary).
History
Although ice houses have been used for thousands of years to provide a source of ice in summer, the first common domestic refrigeration was in the form of ice boxes in the latter years of the 19th Century. As the ice melted it was replaced with ice bought from commercial manufacturers.
In 1856, using the principle of vapour compression, Australian James Harrison produced the world's first practical refrigerator. He was commissioned by a brewery to build a machine that cooled beer.
In 1857, the first refrigerated railway car was introduced by the Chicago meatpacking industry, to prevent spoilage during shipping. In 1866, the first refrigerated railway car to carry fruit was built by Parker Earle of Illinois. The car was used to ship strawberries on the Illinois Central Railroad.
The first domestic refrigerator was apparently manufactured in 1913 by Fred W. Wolf Jnr. in Chicago, and called the DOMELRE (DOMestic ELectric REfrigerator). It was not commercially successful, that distinction apparently going to the Kelvinator Company. This company was formed in May 1916 as the Electro-Automatic Refrigerating Company by Edmund J. Copeland and an industrialist, Arnold H. Gross. The company was renamed within two months to the Kelvinator Company and produced their first model shortly afterwards. Like most of their modern descendents, this refrigerator cooled using a phase change heat pump.
The first refrigerators were of the "remote" type, essentially an upgrade of an existing ice box with the installation of a cooling unit in it, but the motor, compressor and condenser installed either beside it or in the basement. The first self-contained refrigerators were not manufactured until 1925.
The earliest units used toxic refrigerants, typically ammonia (R-717), sulfur dioxide (R-764), or methyl chloride (R-40) as their refrigerant.
The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927. The compressor assembly, which produced substantial 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.
In the early 1920s the industry grew considerably, with some other manufacturers using absorption of ammonia in water instead of liquifying a gas through compression to achieve the phase change. However, these were not very successful, largely because of public prejudice against ammonia as a refrigerant. Today they are used in homes that are not connected to the electric grid, and in recreational vehicles because they can be efficiently powered using a heat source rather than an electric motor.
It was not until 1931 that Dupont produced commercial quantities of R-12, the first refrigerant which was neither toxic nor flammable.
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 37 degrees F is ideal for the refrigerator compartment and 0 degrees F for the freezer. If you suspect a problem, test the temperatures with a refrigerator or outdoor thermometer.
How it works
See Heat pump and Phase change heat pump
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See also
- Gas absorption refrigerator
- Microwave refrigerator combo
- Acoustic refrigeration
- Side-by-side
- Ice and water dispenser
- Ice cube tray
- Defrost (manual, frost free)
- Chiller
- Reversible door
- Compressor
- Sub-Zero Refrigerator
- Thermostat
- Drawers
- Thaw
- Rack (for eggs, bottles,...)
- Star rating
- Noise (dB(A))
- Stainless steel
- Bisque
- Timer
- LED
External links
- Do-it-yourself Appliance Repair Forums Forums by Fixitnow.com Samurai Appliance Repair Man
- History of the Refrigerator - Gizmohighway Technology Guide
- How Refrigerators Work Article by RepairClinic
- Question & Answer Forums Forums by Applianceblog.com
- 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)