refrigeration/Mechanical/Part2

Refrigeration

Refrigeration involves the cooling of bodies and fluids to levels that are below those of the surroundings. Refrigeration involves two processes, one is the absorption of heat at lower temperature, and the other is the rejection of heat to higher temperatures.

When the refrigeration was invented, the sole purpose of this phenomenon then was to produce ice, which would then be used for mainly preserving food, cooling beverages, and refrigerated transport. Today, refrigeration has found many other uses that it is now an essential feature of life. Without refrigeration, the basic fabric of life would be significantly affected. Indeed, in the modern life refrigeration plays an indispensible role. Because of the refrigerator’s contribution, the expiration time of foods can be carried forward; it is now possible to keep fresh foods beyond their typical expiration dates (Hundy, et al 16). Suffice it to say that the refrigeration is one of the most valuable processes in homes today. These magical equipments are craftily made to turn on after every five minutes to keep everything therein cold. Without refrigeration, there would be huge chunks of food that would be going to waste every day.

There are four major application of refrigeration. The four areas are equally important. These are: food processing and preservation; chemical and process industries and special applications.

Food processing and preservation feature of refrigeration also involves distribution. This application integrates the storage of vegetables and raw fruits. Some bacteria cause degradation of food, while enzymatic processing effect on vegetables and fruits case them to ripen more. The refrigerators’ create a law temperature that reduces the growth of these bacteria and enzymatic processes reducing spoilage while improving the food’s shelf life.

The other application of refrigeration involves chemical and process industries. Industries such as petrochemical plants, petroleum refineries and paper pulp industries require extremely large cooling capacities (Chhandra 365). The main application of refrigeration in these key industries involves several fundamental categories. These are separation of gases, condensation of gases, and solidification of solute and dehumidification of air.

The other application of refrigeration involves special application. Apart from the chemical uses, this category looks at other broader applications such as construction units, manufacturing processes and applications in medicine among others. Others in this special category of refrigeration uses include cold treatment of metals, ice skating links, ice manufacture and desolation of water.

The ideal Carnot cycle is a refrigeration cycle that frequently employs constant temperatures external heat source as well as heat sinks. The Carnot cycle is a process where a substance, which in this case is the refrigerant, circulates through four devices. The objective here is to transport heat out of the refrigerator and dumping it into the kitchen. A schematic of the ideal Carnot cycle is illustrated below. In this process, the refrigerant can be an ideal gas which has a constant specific heat; this could for instance be helium (“The Reversal Ideal.”).

Figure 1: Schematic of the Carnot refrigeration cycle

Source: “The Reversal Ideal.” N.d. 2 March, 2014. http://www.eng.fsu.edu/~dommelen/quantum/style_a/qsrev.html

Stability of the refrigerant is very critical because of a number of reasons. The use of an impure refrigerant causes some interrelated changes that collectively compromise the operation, performance, longevity as well as the safety of the system. As such, chemical and thermal stability of the refrigerant is an important consideration in selecting the refrigerant in the refrigeration system.

The trend of using flammable refrigerants seems to be on the rise. There is need to follow for strict procedures and standards when using flammable refrigerants. These refrigerants include hydrocarbons that are being used in both small integrated systems and larger ones as well.

Refrigerant used in food preservation and air conditioning must be non-toxic and non-corrosive in nature. This factor should be considered because these will come into contact with the lives dependent on the system. Refrigerants would negatively affect human health is they were corrosive and toxic in nature.

These two characteristics introduce the issue of environmental considerations of choosing a refrigerant. The two deal with the effect that the refrigerant on the ozone layer and the contribution it has on global warming.

Ammonia remains the most commonly used refrigerant. It is also the most trusted. Ammonia offers some key advantages when used as refrigerant. It is environmentally compatible, has better thermodynamic qualities and has a recognizable odor which makes it its most critical asset. Other industrial refrigerants do not have an odor meaning that if there was a leak it would go undetected.

These refrigerants have proved to be safe and effective becoming the most used refrigerants today. The completely halogenated hydrocarbons are referred to as chlorofluorocarbons (CFCs). In CFC, all hydrogen atoms are substituted with chlorine and fluorine atoms(Chhandra 366).Halogenated hydrocarbons have no negative effect on the atmosphere.

	Cost	Availability	Environmental impact	Performance	Safety	Stability	Toxicity and corrosiveness	Flammability
Ammonia	Low	Highly available	Environmentally compatible	High performance	Safe to use but toxic	Offers stability	Toxic	Not flammable
hydrocarbons	Low		Harmless to ozone layer	Offers great performance	Not harmful		Non corrosive	Highly flammable
CO2	Low	Readily available	Harmless to ozone	Low efficiency	Very safe	excellent stability	Non toxic and non corrosive	Non flammable

The refrigerant that would be best for automobile must combine a number of factors. It must be non flammable, non toxic and have limited impact on the ozone layer and environment in general. The possibility that bets guaranteed this is carbon dioxide. Carbon dioxide is a safe, non-flammable and non-toxic alternative to ammonia and Halogenated hydrocarbons. The reason why CFC would not be appropriate is its serious threat to the environment. When studies on the substance found out that CFC released into the atmosphere tends to accumulate in the stratosphere. This had a depleting effect on the ozone layer. However, CFC is both non corrosive and non toxic. Ammonia is environmentally compatible but it is a toxic gas. As such, the most appropriate refrigeration for an automotive air-conditioning system would be carbon dioxide. Carbon dioxide provided a sustainable solution to automotive air-conditioning system. Indeed, many next generation advances in this area are increasingly experimenting with CO2 in the automotive air conditioning. Sustainability comes with the consideration that this process will involve recycling waste CO2 and using it as a natural refrigerant, therefore turning the problem of CO2 into a workable solution.

Works Cited

Hundy, G.H, Trott, A.R., and Welch, T.C. Refrigeration and Air Conditioning. 4th Edition. Oxford, UK: Elsevier

Chhabra, Raj P. CRC Handbook of Thermal Engineers. New York, CRC Press.

“The Reversal Ideal.” N.d. 2 March, 2014. http://www.eng.fsu.edu/~dommelen/quantum/style_a/qsrev.html

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