Air conditioner

Refrigerator (popular as FRIDGE) is a device or an appliance consisting a thermally insulated room and a methodology to drive out heat from the appliance to the external environment, there by cooling the contents in the appliance to a temperature below normal or ambient. Refrigerators are widely used to store foods which are spoiled at normal temperatures. Bacteria and other food spoiling organisms can’t survive below a certain degree of temperature. A typical fridge contains two compartments, one where the temperature is above the freezing point of water and the second where the temperature is below the freezing point and is known as FREEZER. Before fridges, iceboxes were traditionally used to store food, meat, and fruits.
In olden days, ice houses used to provide cold storage facility for different kinds of foods. These ice houses were first used in Iran. The ice houses were placed near fresh water lakes or packed with snow and ice. Usage of the environment to cool foods is still seen in some places. During winter, placing foods or meat or milk in the snow outside the window will increase the usefulness of the item. William Cullen demonstrated the first known artificial refrigeration process at the University of Glasgow in 1748. He used the vapor compression cycle explained by Michael Faraday. In between the 19th and 20th century, Oliver Evans designed the first refrigeration machine using vapor instead of liquid, Willis Haviland Carrier exhibited the first air conditioner and many other inventors contributed a lot to the development of air cooling machinery. Dr. John Gorrie in 1851 demonstrated an ice maker. Australian James Harrison commenced vapor compression systems for meat packing and breweries industries. In 1922, Carl Munters and Baltzar Von Platen invented absorption refrigeration and was later commercialized successfully by Electrolux.
A fridge works with the help of heat pumps working in a refrigeration cycle. Vapor compression cycle is used mostly in house hold fridges. A circulating refrigerant enters the compressor as vapor at its boiling point. The vapor is then compressed and it exits the compressor as a super heated vapor, which travels through the condenser and removes the heat by cooling the vapor. The vapor also travels through the remaining part of the condenser which condenses into a liquid at its boiling point. This liquid refrigerant passes through the expansion valve which decreases its pressure and it results in the flash evaporation and auto-refrigeration of the liquid (generally only half of the liquid flashes). The partially vaporized refrigerant travels through the tubes of the evaporator. In the evaporator, a fan circulates air across the tube which vaporizes the refrigerant by extracting heat from air which is returned to the food storage. The refrigerant vapor then returns to the compressor inlet which completes the thermodynamic cycle.
An absorption refrigerator is different from a vapor compressor system where heat is used as a source and runs quieter than the later. The peltier effect uses electricity to pump heat. These systems are used where noise is not preferable like camping, but not as energy efficient as other methods.
Some of the typical features of a fridge are automatic defrosting where vapor in the air condenses into frost which builds up into a thick layer of ice. This acts as an insulator, reducing the cooling efficiency of the fridge. So, modern fridges are fitted such that after a certain period of time, a thermostat prompts the fridge to shut off for a certain time there by avoiding the formation of frost ice. Chilled water and ice from an in-door store avoids opening the door frequently. Adjustable shelves and trays for convenient and customized usage of the space. A Cooling zone in the refrigerator door tray to divert air from the freezer zone to the refrigerator door. A status indicator which notifies the time to change the filters. Maximum temperature reached during power failure can be displayed and also information related to foods that contain harmful bacteria. Modern advancements include automatic ice units, self compartmentalized freezer units, multi doored fridges, some extras like radio, DVD player, oven and a television fitted with the fridge