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An Introduction to RefrigerationHow Refrigeration Processes Improve the Quality of Life
Refrigerators and air conditioners owe their performance to the thermodynamic process known as the refrigeration cycle.
On a hot summer day, not much can beat an ice-cold drink or the blast from an air conditioner. These pleasures are possible through the principles of refrigeration. Before modern refrigeration systems were available, people were limited in their methods to keep things cool. Freezing foods for preservation was only possible in winter, when ambient temperatures were below the freezing point. Historical Refrigeration MethodsIce harvesting has been seasonally practiced for thousands of years by many cultures. Ice was cut from lake surfaces and stored in heavily insulated buildings, caves, or pits dug into the ground. Straw was commonly used as an insulator around the blocks of ice. Household insulated “iceboxes” were the precursor to modern refrigerators. The earliest forms of artificial refrigeration were chemical processes. Certain chemicals, when added to water, reduced the temperature of the water, and items could be cooled by immersing them in this water bath. Modern Refrigeration MethodsThe most commonly used form of refrigeration is a thermodynamic process where heat is removed from a heat source and transferred to a heat sink. In the case of a household refrigerator, the interior space of the refrigerator is the heat source, and the air outside of the refrigerator is the heat sink. To achieve the effect of cooling a space to temperatures below ambient temperatures, certain components are required, and the components must be combined in a specific order to achieve the cooling effect. This type of refrigeration is known as a vapor-compression cycle and has a four-step thermal cycle:
Through this cycle, a refrigeration system can continue to remove heat from a space until the performance limits of the refrigerant and the refrigerator components are reached. Other types of refrigeration methods include the vapor absorption cycle using water-ammonia systems, the gas cycle, which is similar to the vapor-compression cycle except the refrigerant remains in a gaseous phase throughout the cycle; thermoelectric refrigeration, and magnetic refrigeration. These methods are generally not suitable for household or industrial use, although they have their own niche applications. RefrigerantsRefrigeration systems use specific compounds called refrigerants as working fluids. Refrigerants have the capability of absorbing heat from its surroundings while at a low temperature and pressure and expelling heat while at a high temperature and pressure. During the 1980s, it was found that many compounds used as refrigerants were contributing to the degradation of the Earth’s ozone layer. The primary culprit was chlorofluorocarbons (CFCs), which were extremely damaging when released into the atmosphere. Currently, many household refrigerators and air conditioning systems use R-22 also known as Freon. R-22 is a hydrochlorofluorocarbon (HCFC). HCFC’s are much less damaging to the ozone layer than CFCs, but their handling, recycling, and disposal are highly regulated to reduce the chances of these refrigerants from being released into the atmosphere. Refrigeration processes allow for the safe storage and preservation of food and allow people to live and work in comfortable conditions when outdoor temperatures are high.
The copyright of the article An Introduction to Refrigeration in Mechanical Engineering is owned by Susan Kristoff. Permission to republish An Introduction to Refrigeration in print or online must be granted by the author in writing.
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