History and Application of Refrigeration

8/8/2019 History and Application of Refrigeration

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Introduction

Refrigeration is the process of removing heat from anenclosed space, or from a substance, and moving it to a placewhere it is unobjectionable. The primary purpose ofrefrigeration is lowering the temperature of the enclosedspace or substance and then maintaining that lower

temperature. The term cooling refers generally to any naturalor artificial process by which heat is dissipated. The process ofartificially producing extreme cold temperatures is referred toas cryogenics.

Cold is the absence of heat, hence in order to decrease atemperature, one "removes heat", rather than "adding cold."In order to satisfy the Second Law of Thermodynamics, someform of work must be performed to accomplish this. Thiswork is traditionally done by mechanical work but can also bedone by magnetism, laser or other means.


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Natural Refrigeration

In olden days refrigeration was achieved by naturalmeans such as the use of ice or evaporative cooling. Inearlier times, ice was either:

Transported from colder regions,

Harvested in winter and stored in ice houses for summeruse or,

Made during night by cooling of water by radiation tostratosphere.


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Art of Ice making by Nocturnal Cooling

The art of making ice by nocturnal cooling wasperfected in India. In this method ice was made bykeeping a thin layer of water in a shallow earthen

tray, and then exposing the tray to the night sky.Compacted hay of about 0.3 m thickness was used asinsulation. The water looses heat by radiation to thestratosphere, which is at around -55C and by early

morning hours the water in the trays freezes to ice.This method of ice production was very popular inIndia.


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Evaporative Cooling

As the name indicates, evaporative cooling is the process of reducing thetemperature of a system by evaporation of water. Human beings perspireand dissipate their metabolic heat by evaporative cooling if the ambienttemperature is more than skin temperature. Animals such as thehippopotamus and buffalo coat themselves with mud for evaporativecooling. Evaporative cooling has been used in India for centuries to obtain

cold water in summer by storing the water in earthen pots. The waterpermeates through the pores of earthen vessel to its outer surface where itevaporates to the surrounding, absorbing its latent heat in part from thevessel, which cools the water. It is said that Patliputra University situatedon the bank of river Ganges used to induce the evaporative-cooled air fromthe river. Suitably located chimneys in the rooms augmented the upwardflow of warm air, which was replaced by cool air. Evaporative cooling by

placing wet straw mats on the windows is also very common in India. Thestraw mat made from khus adds its inherent perfume also to the air.Now-a-days desert coolers are being used in hot and dry areas to providecooling in summer.


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Cooling by Salt Solutions

Certain substances such as common salt, whenadded to water dissolve in water and absorb its heatof solution from water (endothermic process). This

reduces the temperature of the solution (water+salt).Sodium Chloride salt (NaCl) can yield temperaturesup to -20C and Calcium Chloride ((CaCl2 ) up to -50C in properly insulated containers. However, as it

is this process has limited application, as thedissolved salt has to be recovered from its solution byheating.


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Artificial Refrigeration

Refrigeration as it is known these days is producedby artificial means. Though it is very difficult tomake a clear demarcation between natural andartificial refrigeration, it is generally agreed that thehistory of artificial refrigeration began in the year1755, when the Scottish professor William Cullenmade the first refrigerating machine, which couldproduce a small quantity of ice in the laboratory.

Based on the working principle, refrigerationsystems can be classified as vapour compressionsystems, vapour absorption systems, gas cyclesystems etc.


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Vapour Compression RefrigerationSystems

y The basis of modern refrigeration is the ability ofliquids to absorb enormous quantities of heat as they

boil and evaporate.

Apparatus described by Jacob Perkins in his patent specification

of 1834. The refrigerant (ether or other volatile fluid) boils in

evaporator B taking heat from surrounding water in container

A. The pump C draws vapour away and compresses it to higher

pressure at which it can condense to liquids in tubes D, giving

out heat to water in vessel E. Condensed liquid flows throughthe weight loaded valve H, which maintains the difference of

pressure between the condenser and evaporator. The small

pump above H is used for charging the apparatus with

refrigerant.


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If this process of cooling is to be made continuous thevapors have to be recycled by condensation to the liquidstate. The condensation process requires heat rejectionto the surroundings. It can be condensed at atmospheric

temperature by increasing its pressure. The process ofcondensation was learned in the second half ofeighteenth century. U.F. Clouet and G. Monge liquefiedSO2 in 1780 while van Marum and Van Troostwijkliquefied NH3 in 1787. Hence, a compressor is required to

maintain a high pressure so that the evaporating vapourscan condense at a temperature greater than that of thesurroundings


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Perkins machine built by John Hague


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Domestic refrigeration systems

The domestic refrigerator using natural ice (domesticice box) was invented in 1803 and was used foralmost 150 years without much alteration. The

domestic ice box used to be made of wood withsuitable insulation. Ice used to be kept at the top ofthe box, and low temperatures are produced in the

box due to heat transfer from ice by natural

convection.A

drip pan is used to collect the waterformed due to the melting of ice.


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Domestic refrigeration systems

The initial domestic refrigerators used mainly sulphurdioxide as refrigerant.

General Electric Company introduced the firstrefrigerator with a hermetic compressor in 1926.

The domestic refrigerator based on absorption principleas proposed by Platen and Munters, was first made byElectrolux Company in 1931 in Sweden.

In Japan the first mechanical domestic refrigerator was

made in 1924. The first dual temperature (freezer-refrigerator)

domestic refrigerator was introduced in 1939


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Vapour Absorption Refrigeration Systems

y John Leslie in 1810 kept H2SO4 and water in two separate jarsconnected together. H2SO4 has very high affinity for water. It absorbswater vapour and this becomes the principle of removing theevaporated water vapour requiring no compressor or pump. H2SO4 isan absorbent in this system that has to be recycled by heating to get ridof the absorbed water vapour, for continuous operation.


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Steam Jet Refrigeration System

y If water is sprayed into a chamber where a low pressure is maintained, a part ofthe water will evaporate. The enthalpy of evaporation will cool the remainingwater to its saturation temperature at the pressure in the chamber. Obviouslylower temperature will require lower pressure. Water freezes at 0oC hencetemperature lower than 4oC cannot be obtained with water. In this system, high

velocity steam is used to entrain the evaporating water vapour.


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Thermoelectric Refrigeration Systems

y In 1821 the German physicist T.J. Seebeck reported that when two junctions ofdissimilar metals are kept at two different temperatures, an electro motiveforce (emf) is developed, resulting in flow of electric current. The emf producedis found to be proportional to temperature difference. In 1834, a Frenchmen, J.Peltier observed the reverse effect, i.e., cooling and heating of two junctions of

dissimilar materials when direct current is passed through them, the heattransfer rate being proportional to the current .


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Applications

yWidespread commercial use

y Home and consumer use

y Refrigeration is used to liquify gases like oxygen,

nitrogen, propane and methane for example. Incompressed air purification, it is used to condense

water vapor from compressed air to reduce itsmoisture content.

y Dairy products are constantly in need ofrefrigeration


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y www.rogersrefrig.com

y www.wikipedia.org

y inventors.about.com

y www.history-magazine.com


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Documents

History and Application of Refrigeration