20-04-2011, 04:02 PM
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ABSTRACT
Ever growing demand of the refrigeration and air conditioning systems in different disciplines expects major modifications in the working mechanisms, which ultimately influences the Environment. The alternate eco-friendly systems are to be designed to overcome the hazards such as ODP, GWP caused by the mechanical refrigeration systems.
This paper discusses about ‘Magnetic Refrigeration’ which is based on the principle of Magnetocaloric Effect. Magnetic refrigeration systems are an environmentally attractive space cooling and refrigeration alternative that do not use a fluorocarbon working fluid.
The newly introduced Adiabatic Demagnetization Refrigerator which uses cyclic cooling promises a clean, pollution free environment with efficient cooling.
KEY WORDS: - ODP, GWP, Magnetocaloric Effect, Adiabatic demagnetization.
1. Introduction
Man has always had a need for preserving food and it has probably been known for a long time that low temperatures allow fresh food to be kept for long periods of time. The first method that was used was to collect and store natural ice during the winter to be used later during the warmer periods of the year. This low temperature preserving is termed as’ Refrigeration’. Now a days, refrigeration applications at the domestic, commercial, industrial level are becoming an integral part. Our changing lifestyle leads to more demand and supply for refrigeration systems. The entire concept of refrigeration is based upon Thermodynamic theory.
1.1 Mechanical Refrigeration system:
A device that transfers heat from a cold body to a warm body, with the aid of an external energy source is called as a Refrigerator. The invention of Joule-Thomson’s cooling effect (i.e. when a fluid is allowed to expand through a nozzle, it gets cooled) and its combination with compression gave rise to the Mechanical/Vapour compression Refrigeration technology.
In such a system, the low temperature (evaporator) reservoir is the cold body and from where the stored substances get cooled and the high temperature reservoir(condenser) is the hot body ,from where the heat is given off to surroundings. The two main types of refrigeration cycles are the refrigerant absorption process and the vapour compressor refrigeration cycle. The compressor cycle absorbs heat in an evaporator when the refrigerant vaporizes. This vapour is then compressed by a compressor and then condensed at the higher pressure in a condenser while emitting heat. The liquefied refrigerant is then returned to the low pressure evaporator via a pressure reducing expansion device. The refrigerant that was initially used was ammonia and this and other refrigerants such as sulphur dioxide, methyl chloride and carbon dioxide were in common use. The introduction of CFC-compounds (halogenated hydrocarbons, Freon©, etc.) refrigerants that were at that time considered to be harmless to humans, environmentally safe and incombustible .CFC-compounds where further developed and rapidly replaced the previously used refrigerants except ammonia.
2. Refrigerants and the Environment
CFC-compounds have a significant destructive effect on the earth's Ozone layer that protects us from the sun's UV-radiation. CFCs are very stable and can disperse high in the stratosphere where they decompose and form free chlorine. The chlorine then acts as a catalyst that reacts with the Ozone.
A replacement has been sought for R11, trichlorofluorinemethane, R12, dichlorofluoromethane and R502 (R115+R22) in refrigeration application. These compounds are considered to be the most damaging to the ozone layer and are also the refrigerants that have the most widespread use. The two main environment concerns are discussed below.
2.1 Ozone Depletion Potential (ODP)
With growing environment hazards, awareness towards a sustainable development is increasing now. One of the serious threats to the environment is the Stratospheric Ozone Layer Depletion. The stratospheric ozone layer plays a beneficial role by absorbing most of the biologically damaging ultraviolet sunlight called UV-B coming towards the earth. Ozone also plays a key role in the temperature regulation of the Earth’s atmosphere. Recent investigations have shown those human made chemicals are responsible for the observed depletion of ozone layer. The Ozone depleting compounds (CFCs and HCFC) contain reactive gaseous atoms of chlorine or bromine. These atoms when leaked from the refrigeration system cause hazard. Although, these molecules are heavier than the molecules of air, the atmospheric air circulation takes these compounds to the stratosphere over a period of time.CFCs are very stable and can disperse high in the stratosphere where they decompose and form free chlorine. The chlorine then acts as a catalyst that reacts with the ozone. Halon (i.e. chlorine and bromine) molecules of CFCs and HCFCs react very rapidly with ozone via their oxide formation and thus decrease in concentration of stratospheric ozone.
ABSTRACT
Ever growing demand of the refrigeration and air conditioning systems in different disciplines expects major modifications in the working mechanisms, which ultimately influences the Environment. The alternate eco-friendly systems are to be designed to overcome the hazards such as ODP, GWP caused by the mechanical refrigeration systems.
This paper discusses about ‘Magnetic Refrigeration’ which is based on the principle of Magnetocaloric Effect. Magnetic refrigeration systems are an environmentally attractive space cooling and refrigeration alternative that do not use a fluorocarbon working fluid.
The newly introduced Adiabatic Demagnetization Refrigerator which uses cyclic cooling promises a clean, pollution free environment with efficient cooling.
KEY WORDS: - ODP, GWP, Magnetocaloric Effect, Adiabatic demagnetization.
1. Introduction
Man has always had a need for preserving food and it has probably been known for a long time that low temperatures allow fresh food to be kept for long periods of time. The first method that was used was to collect and store natural ice during the winter to be used later during the warmer periods of the year. This low temperature preserving is termed as’ Refrigeration’. Now a days, refrigeration applications at the domestic, commercial, industrial level are becoming an integral part. Our changing lifestyle leads to more demand and supply for refrigeration systems. The entire concept of refrigeration is based upon Thermodynamic theory.
1.1 Mechanical Refrigeration system:
A device that transfers heat from a cold body to a warm body, with the aid of an external energy source is called as a Refrigerator. The invention of Joule-Thomson’s cooling effect (i.e. when a fluid is allowed to expand through a nozzle, it gets cooled) and its combination with compression gave rise to the Mechanical/Vapour compression Refrigeration technology.
In such a system, the low temperature (evaporator) reservoir is the cold body and from where the stored substances get cooled and the high temperature reservoir(condenser) is the hot body ,from where the heat is given off to surroundings. The two main types of refrigeration cycles are the refrigerant absorption process and the vapour compressor refrigeration cycle. The compressor cycle absorbs heat in an evaporator when the refrigerant vaporizes. This vapour is then compressed by a compressor and then condensed at the higher pressure in a condenser while emitting heat. The liquefied refrigerant is then returned to the low pressure evaporator via a pressure reducing expansion device. The refrigerant that was initially used was ammonia and this and other refrigerants such as sulphur dioxide, methyl chloride and carbon dioxide were in common use. The introduction of CFC-compounds (halogenated hydrocarbons, Freon©, etc.) refrigerants that were at that time considered to be harmless to humans, environmentally safe and incombustible .CFC-compounds where further developed and rapidly replaced the previously used refrigerants except ammonia.
2. Refrigerants and the Environment
CFC-compounds have a significant destructive effect on the earth's Ozone layer that protects us from the sun's UV-radiation. CFCs are very stable and can disperse high in the stratosphere where they decompose and form free chlorine. The chlorine then acts as a catalyst that reacts with the Ozone.
A replacement has been sought for R11, trichlorofluorinemethane, R12, dichlorofluoromethane and R502 (R115+R22) in refrigeration application. These compounds are considered to be the most damaging to the ozone layer and are also the refrigerants that have the most widespread use. The two main environment concerns are discussed below.
2.1 Ozone Depletion Potential (ODP)
With growing environment hazards, awareness towards a sustainable development is increasing now. One of the serious threats to the environment is the Stratospheric Ozone Layer Depletion. The stratospheric ozone layer plays a beneficial role by absorbing most of the biologically damaging ultraviolet sunlight called UV-B coming towards the earth. Ozone also plays a key role in the temperature regulation of the Earth’s atmosphere. Recent investigations have shown those human made chemicals are responsible for the observed depletion of ozone layer. The Ozone depleting compounds (CFCs and HCFC) contain reactive gaseous atoms of chlorine or bromine. These atoms when leaked from the refrigeration system cause hazard. Although, these molecules are heavier than the molecules of air, the atmospheric air circulation takes these compounds to the stratosphere over a period of time.CFCs are very stable and can disperse high in the stratosphere where they decompose and form free chlorine. The chlorine then acts as a catalyst that reacts with the ozone. Halon (i.e. chlorine and bromine) molecules of CFCs and HCFCs react very rapidly with ozone via their oxide formation and thus decrease in concentration of stratospheric ozone.
