Thursday 19 December 2013

BRIEF HISTORY OF REFRIGERATION

In the past around 4000 years from now, people in India and Egypt are known to produce ice by keeping water in the porous pots outside the home during the night period. The evaporation of water in almost cool dry air and radiative heat transfer between the water and the deep sky that is at a very low temperature (much below the freezing point of ice) caused the formation of ice even though the surrounding air was at a higher temperature than the freezing point of water. There are a few accounts in China about the use of ice around 1000 BC for cooling the beverages. In 4th century A.D., East Indians were producing ice by dissolving salt in water.
Because of the very small amount of production, the aforesaid methods were not feasible for commercial applications. Natural ice is limited to certain regions, therefore, the absence of good quality insulation systems in those days forced the man to develop methods to produce ice artificially. Out of many pioneers’ work on refrigeration side, a few are presented here. In 1790 the first British Patent was obtained by Thomas Hariss and John Long. In 1834 Jacob Perkins developed a hand operated refrigeration system using ether as the working fluid (Figure 1.5). Ether vapor was sucked by the hand operated compressor and then high temperature and pressure ether vapor was condensed in the water cooled chamber that served as the condenser. Liquid ether was finally throttled to the lower pressure, which was then evaporated in a chamber called evaporator, A. With the evaporation, temperature of the water surrounding the evaporator fell down and finally the ice was formed. In this system, either was used again and again in the cyclic process with negligible wastage.


The first American patent of a cold air machine to produce ice in order to cure people suffering from high fever was obtained by Dr. John Gorrie of Florida in 1851. In 1860, instead of air or ether, Dr. James Harrison of Australia used sulfuric ether. This was the world’s first installation of refrigeration machine for brewery. In 1861, Dr. Alexander Kirk of England constructed a cold air machine similar to that of Dr. Gorrie. In hismachine, air was compressed by a reciprocating compressor driven by a steam engine running on coal.
In the 19th century, there was remarkable development of refrigeration systems to replace natural ice by artificial ice producing machines. In the beginning of the 20th century, large sized refrigeration machines were developed. In 1904 in the New York Stock Exchange, about 450 ton cooling machine was installed. In Germany, people used air conditioning in theater. Around 1911 the compressors with speed between 100 to 300 rpm were developed. In 1915, the first two-stage modern compressor was developed.
To meet the demand for ice during the civil war, Ferdinand Carre of the USA developed a vapor-absorption refrigeration system (Figure 1.6) using ammonia and water. Carre’s system consisted of an evaporator, an absorber, a pump, a generator, a condenser and an expansion device. The evaporated vapor is absorbed by the week ammonia-water mixture in the absorber yielding strong aqua ammonia. The pump delivers this strong solution into generator where heat transfer from a burner separates ammonia vapor and the weak ammonia returns to the absorber. On the other hand the ammonia vapor condenses in the condenser before being throttled. The throttled liquid ammonia enters the evaporator resulting in completion of the cyclic process.


      Until about 1920s the development in refrigeration system was restricted to the refinement in the cold-air machines and vapor-compression systems. After 1920s, there has been extensive diversification in the growth of refrigeration systems leading to new developments such as vortex tube, thermoelectric, pulse-tube, steam-jet, centrifugal compression systems, etc. The most important development can be the invention of new refrigerants which were chlorfluoro hydrocarbons. This development occurred in 1930 in GE Corporation of USA at a time when Refrigeration industry had begun to stagnate on the use of NH3 SO2 as refrigerant. The chlorfluor carbons offered the advantages of best refrigerants and were proven non-toxic substances in comparison with NH3 and SO2 Other developments took place due to special requirements to utilize waste heat or low grade energy or materials of specific properties for thermoelectric effect. Owing to the likelihood of energy crisis in the future, many commercial units have been developed that utilizes waste heat or solar energy                                                                                                                                                                                             



difference b/w refrigeration and air conditioning

Air-conditioning is a process that simultaneously conditions air; distributes it combined with the outdoor
air to the conditioned space; and at the same time controls and maintains the required space’s temperature,
humidity, air movement, air cleanliness, sound level, and pressure differential within predetermined
limits for the health and comfort of the occupants, for product processing, or both.

Refrigeration is the cooling effect of the process of extracting heat from a lower temperature heat source,
a substance or cooling medium, and transferring it to a higher temperature heat sink, probably atmospheric
air and surface water, to maintain the temperature of the heat source below that of the surroundings.

refrigeration system, removing heat from closed space.

GEOMETRY/STRUCTURE:
Refrigerant, compressor, expansion valve (flow control device), evaporator, condenser, pipes and tubes.
Skematic of Compression Refrigeration System

EXPLANATION OF HOW IT WORKS/ IS USED:
Refrigerant flows through the compressor, which raises the pressure of the refrigerant. Next the refrigerant flows through the condenser, where it condenses from vapor form to liquid form, giving off heat in the process. The heat given off is what makes the condenser "hot to the touch." After the condenser, the refrigerant goes through the expansion valve, where it experiences a pressure drop. Finally, the refrigerant goes to the evaporator. The refrigerant draws heat from the evaporator which causes the regrigerant to vaporize. The evaporator draws heat from the region that is to be cooled. The vaporized refrigerant goes back to the compressor to restart the cycle.
More Detail:
Compressor: Of the reciprocating, rotary, and centrifugal compressors, the most popular among domestic or smaller power commercial refrigeration is the reciprocating. The reciprocating compressor is similar to an automobile engine. A piston is driven by a motor to "suck in" and compress the refrigerant in a cylinder. As the piston moves down into the cylinder (increasing the volume of the cylinder), it "sucks" the refrigerant from the evaporator. The intake valve closes when the refrigerant pressure inside the cylinder reaches that of the pressure in the evaporator. When the piston hits the point of maximum downard displacement, it compresses the refrigerant on the upstroke. The refrigerant is pushed through the exhaust valve into the condenser. Both the intake and exhaust valves are designed so that the flow of the refrigerant only travels in one direction through the system.
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Diagram of Compressor (Belt Driven In This Instance)

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Detail of Compressor Valve Function

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Components of Compresion Refrigeration In A Dorm Refrigerator
Condenser: The condenser removes heat given off during the liquefication of vaporized refrigerant. Heat is given off as the temperature drops to condensation temperature. Then, more heat (specifically the latent heat of condensation) is released as the refrigerant liquefies. There are air-cooled and water-cooled condensers, named for their condensing medium. The more popular is the air-cooled condenser. The condensers consist of tubes with external fins. The refrigerant is forced through the condenser. In order to remove as much heat as possible, the tubes are arranged to maximize surface area. Fans are often used to increase air flow by forcing air over the surfaces, thus increasing the condenser capability to give off heat.
Evaporator: This is the part of the refrigeration system that is doing the actual cooling. Because its function is to absorb heat into the refrigeration system (from where you don't want it), the evaporator is placed in the area to be cooled. The refrigerant is let into and measured by a flow control device, and eventually released to the compressor. The evaporator consists of finned tubes, which absorbs heat from the air blown through a coil by a fan. Fins and tubes are made of metals with high thermal conductivity to maximize heat transfer. The refrigerant vaporizes from the heat it absorbs heat in the evaporator.
Flow control device (expansion valve): This controls the flow of the liquid refrigerant into the evaporator. Control devices usually are thermostatic, meaning that they are responsive to the temperature of the refrigerant.

DOMINANT PHYSICS:

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