International Journal of Science and Research (IJSR)

ISSN (Online): 2319-7064

Impact Factor (2012): 3.358

A Study on Refrigeration
Poonam Dhankhar
M. Tech, G.J.U.S & T Hissar, Haryana, India

Abstract: Refrigeration is a basic method of food preservation. All the refrigeration methods for food preservation are based on
Reverse Carnot cycle, which explains Adiabatic and Isothermal Expansion and Compression. Basic components used in these cycles are
Evaporator, Compressor, Condenser and Expansion Valve. Generally used cycle is Vapor Compression Cycle. Other cycles are Vapor
Absorption Cycle, Gas Cycle. Other new methods of Refrigeration are Thermoelectric and Magnetic Refrigeration. Various types of
refrigerants are used in these cycles based upon their properties. Commercially Refrigeration is used as preservation method in various
food industries like Dairy and Meat Processing industry.
 
Keywords: Food preservation, reverse carnot cycle, evaporator, compressor, condenser, vapor compression cycle, Thermoelectric and
Magnetic Refrigeration 
 
1. Introduction [1] [4] Englander Frederic Tudor, who became known as the
"Ice King", worked on developing better insulation
Refrigeration is a process in which work is done to remove products for the long distance shipment of ice, especially to
heat from one location to another. Refrigeration has many the tropics.
applications including but not limited to household
refrigerators, industrial freezers, cryogenics, air First refrigeration systems:-  The first known method of
conditioning, and heat pumps. In order to satisfy the Second artificial refrigeration was demonstrated by William Cullen
Law of Thermodynamics, some form of work must be at the University of Glasgow in Scotland in 1756. Cullen
performed to accomplish this. The work is traditionally done used a pump to create a partial vacuum over a container of
by mechanical work but can also be done by magnetism, diethyl ether, which then boiled, absorbing heat from the
laser or other means. Since the turn of the century, there has surrounding air. The experiment even created a small
been steady growth of application of refrigeration in amount of ice, but had no practical application at that time. 
preservation of perishable food products, agriculture and
fishery. In 1758, Benjamin Franklin and John Hadley, professor of
  chemistry at Cambridge University, conducted an
The purpose of refrigeration for food is to retard experiment to explore the principle of evaporation as a
deterioration by micro-organisms, chemical and physical means to rapidly cool an object. Franklin and Hadley
processes. By cooling at temperatures just above freezing it confirmed that evaporation of highly volatile liquids such as
is possible to achieve a limited extension of storage time alcohol and ether could be used to drive down the
which is often sufficient for safe distribution and marketing. temperature of an object past the freezing point of water.
By freezing to temperature as low as -30ᴼC, deterioration They conducted their experiment with the bulb of a mercury
can be slowed down further and this increases the storage thermometer. They lowered the temperature of the
time. Refrigeration has applications in diverse industries, thermometer bulb down to 7 °F (−14 °C) while the ambient
such as manufacturing chemicals, petroleum, refineries, temperature was 65 °F (18 °C). Franklin noted that soon
paper and pulp industries also. after they passed the freezing point of water (32 °F) a thin
  film of ice formed on the surface of the thermometer's bulb
and that the ice mass was about a quarter inch thick when
2. Review of Literature [6] they stopped the experiment upon reaching 7 °F (−14 °C).  
In 1820, the British scientist Michael Faraday liquefied
Ice harvesting:‐  The use of ice to refrigerate and thus
ammonia and other gases by using high pressures and low
preserve food goes back to prehistoric times. Through the temperatures. 
ages, the seasonal harvesting of snow and ice was a regular
practice of most of the ancient cultures: Chinese, Hebrews, An American living in Great Britain, Jacob Perkins,
Greeks, Romans, Persians. Ice and snow were stored in obtained the first patent for a vapor-compression
caves or dugouts lined with straw or other insulating refrigeration system in 1834. In 1842, an American
materials. The Persians stored ice in pits called yakhchals. physician, John Gorrie, designed the first system for
Rationing of the ice allowed the preservation of foods over refrigerating water to produce ice. His system compressed
the warm periods. This practice worked well down through air, then partially cooled the hot compressed air with water
the centuries, with ice houses remaining in use into the before allowing it to expand while doing part of the work
twentieth century. In the 16th century, the discovery of required to drive the air compressor. That isentropic (the
chemical refrigeration was one of the first steps toward process takes place from initiation to completion without an
artificial means of refrigeration. Sodium nitrate or increase or decrease in the entropy of the system, i.e., the
potassium nitrate, when added to water, lowered the water entropy of the system remains constant) expansion cooled
temperature and created a sort of refrigeration bath for the air to a temperature low enough to freeze water and
cooling substances. During the first half of the 19th century, produce ice, or to flow "through a pipe for effecting
ice harvesting became big business in America. New
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 International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Impact Factor (2012): 3.358
refrigeration otherwise" as stated in his patent granted by the frozen foods, fruit and vegetables, and temperature-sensitive
U.S. Patent Office in 1851.Gorrie built a working prototype chemicals. Most modern refrigerators keep the temperature
(A prototype is an early sample or model built to test a between -40 and 20 °C and have a maximum payload of
concept or process or to act as a thing to be replicated or around 24,000 kg gross weight (in Europe). 
learned from), but his system was a commercial failure.
  b) Home and consumer use
Alexander Twining began experimenting with vapor- With the invention of synthetic refrigerants based mostly on
compression refrigeration in 1848 and obtained patents in a chlorofluorocarbon (CFC) chemical, safer refrigerators
1850 and 1853. He is credited with having initiated were possible for home and consumer use. Freon is a
commercial refrigeration in the United States by 1856. trademark of the DuPont Corporation and refers to these
  CFC, and later hydro chlorofluorocarbon (HCFC) and hydro
The first gas absorption refrigeration system using gaseous fluorocarbon (HFC), refrigerants developed in the late
ammonia dissolved in water (referred to as "aqua ammonia") 1920s. These refrigerants were considered at the time to be
was developed by Ferdinand Carré of France in 1859 and less harmful than the commonly used refrigerants of the
patented in 1860. Due to the toxicity of ammonia, such time, including methyl formate, ammonia, methyl chloride,
systems were not developed for use in homes, but were used and sulfur dioxide. The intent was to provide refrigeration
to manufacture ice for sale. equipment for home use without danger: these CFC
  refrigerants answered that need. However, in the 1970s the
Thaddeus Lowe, an American balloonist from the Civil compounds were found to be reacting with atmospheric
War, had experimented over the years with the properties of ozone, an important protection against solar ultraviolet
gases. One of his mainstay enterprises was the high-volume radiation, and their use as a refrigerant worldwide was
production of hydrogen gas. He also held several patents on curtailed in the Montreal Protocol of 1987.
ice making machines. His "Compression Ice Machine"
would revolutionize the cold storage industry. In 1869 he 3. Basic Refrigeration Principle [4] [5]
and other investors purchased an old steamship onto which
they loaded one of Lowe’s refrigeration units and began If you were to place a hot cup of coffee on a table and leave
shipping fresh fruit from New York to the Gulf Coast area, it for a while, the heat in the coffee would be transferred to
and fresh meat from Galveston, Texas back to New York. the materials in contact with the coffee, i.e. the cup, the table
Because of Lowe’s lack of knowledge about shipping, the and the surrounding air. As the heat is transferred, the coffee
business was a costly failure, and it was difficult for the in time cools. Using the same principle, refrigeration works
public to get used to the idea of being able to consume meat by removing heat from a product and transferring that heat
that had been so long out of the packing house. to the outside air.
   
Domestic mechanical refrigerators became available in the Refrigeration is used to cool products. The refrigeration
United States around 1911. system (R) transfers heat from a cooler low-energy reservoir
to a warmer high-energy reservoir 
a) Widespread commercial use
By the 1870s breweries had become the largest users of
commercial refrigeration units, though some still relied on
harvested ice. Though the ice-harvesting industry had grown
immensely by the turn of the 20th century, pollution and
sewage had begun to creep into natural ice making it a
problem in the metropolitan suburbs. Eventually breweries
began to complain of tainted ice. This raised demand for
more modern and consumer-ready refrigeration and ice-
making machines. In 1895, German engineer Carl von
Linde set up a large-scale process for the production of
liquid air and eventually liquid oxygen for use in safe
household refrigerators.
 
  Figure 1: Schematic representation of refrigeration
Refrigerated railroad cars were introduced in the US in the system 
1840s for the short-run transportation of dairy products.    
By 1900, the meat packing houses of Chicago had adopted
4. Refrigeration System Components [5]
ammonia-cycle commercial refrigeration. By 1914, almost
There are five basic components of a refrigeration system,
every location used artificial refrigeration. The big meat
these are: Evaporator, Compressor, Condenser, Expansion
packers, Armour, Swift, and Wilson, had purchased the
Valve and Refrigerant- to conduct the heat from the product.
most expensive units which they installed on train cars and
In order for the refrigeration cycle to operate successfully
in branch houses and storage facilities in the more remote
each component must be present within the refrigeration
distribution areas.It was not until the middle of the 20th
system. 
century that refrigeration units were designed for installation
on tractor-trailer rigs (trucks or Lorries). Refrigerated
vehicles are used to transport perishable goods, such as
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Impact Factor (2012): 3.358
4.1 The Evaporator  Magnetic Refrigeration 
 Other Methods 
The purpose of the evaporator is to remove unwanted heat
from the product, via the liquid refrigerant. The liquid 5.1 Non-cyclic refrigeration 
refrigerant contained within the evaporator is boiling at a
low-pressure. The level of this pressure is determined by two In non-cyclic refrigeration, cooling is accomplished by
factors: melting ice or by subliming dry ice (frozen carbon dioxide).
  These methods are used for small-scale refrigeration such as
 The rate at which the heat is absorbed from the product to in laboratories and workshops, or in portable coolers. Ice
the liquid refrigerant in the evaporator  owes its effectiveness as a cooling agent to its constant
 The rate at which the low-pressure vapour is removed melting point of 0 °C (32 °F). In order to melt, ice must
from the evaporator by the compressor  absorb 333.55 kJ/kg (approx. 144 Btu/lb) of heat. Foodstuffs
 To enable the transfer of heat, the temperature of the maintained at this temperature or slightly above have an
liquid refrigerant must be lower than the temperature of increased storage life. Solid carbon dioxide has no liquid
the product being cooled. Once transferred, the liquid phase at normal atmospheric pressure, so sublimes directly
refrigerant is drawn from the evaporator by the from the solid to vapor phase at a temperature of -78.5 °C (-
compressor via the suction line. When leaving the 109.3 °F), and is therefore effective for maintaining products
evaporator coil the liquid refrigerant is in vapor form.  at low temperatures during the period of sublimation
  (Sublimation refers to the process of transition of a
4.2 The Compressor  substance from the solid phase to the gas phase without
passing through an intermediate liquid phase). Systems such
The purpose of the compressor is to draw the low- as this where the refrigerant evaporates and is vented into
temperature, low-pressure vapour from the evaporator via the atmosphere are known as "total loss refrigeration".
the suction line. When vapour is compressed it rises in  
temperature. Therefore, the compressor transforms the 5.1.1 Ice Refrigeration
vapour from a low-temperature vapor to a high-temperature In this method the ordinary ice is used for keeping the space
vapour, in turn increasing the pressure. The vapor is then at temperature below the surrounding temperature. The
released from the compressor in to the discharge line. temperature of ice is considered to be 0 degree Celsius hence
  it can be used to maintain the temperatures of about 5 to 10
4.3 The Condenser  degree Celsius. To use the ice for refrigerating effect a
closed and insulated chamber is required. On one side of the
The purpose of the condenser is to extract heat from the chamber ice is kept while on the other side there is a space
refrigerant to the outside air. Fans mounted above the which is to be cooled where some material to be cooled can
condenser unit are used to draw air through the condenser be placed. If the temperature below 0 degree Celsius is
coils. The temperature of the high-pressure vapour required, then the mixture of ice and salt is used. This
determines the temperature at which the condensation method of cooling is still being used for cooling the cold
begins. As heat has to flow from the condenser to the air, the drinks, keeping the water chilled in thermos, etc.
condensation temperature must be higher than that of the air;  
usually between - 12°C and -1°C. The high-pressure vapour 5.1.2 Dry ice refrigeration
within the condenser is then cooled to the point where it Dry ice is the solid carbon dioxide having the temperature of
becomes a liquid refrigerant once more, whilst retaining -78 degree Celsius. Dry ice converts directly from solid state
some heat. The liquid refrigerant then flows from the to gaseous; this process is called as sublimation. Dry ice can
condenser in to the liquid line. be pressed into various sizes and shapes as blocks or slabs.
  Dry ice is usually packed in the frozen food cartons along
4.4 The Expansion Valve  with the food that has to be kept frozen for long intervals of
time. When the dry ice gets converted into vapor state it
Within the refrigeration system, the expansion valve is keeps the food frozen. The process of dry ice refrigeration is
located at the end of the liquid line, before the evaporator. now-a-days being used for freezing the food in aircraft
The high-pressure liquid reaches the expansion valve, transportation. The non-cyclic methods of refrigeration can
having come from the condenser. The valve then reduces the be used only in places where small amount of refrigeration is
pressure of the refrigerant as it passes through the orifice, required in places like laboratories, workshops, water
which is located inside the valve. On reducing the pressure, coolers, small old drink shops, small hotels etc.
the temperature of the refrigerant also decreases to a level  
below the surrounding air. This low-pressure, low 5.2 Cyclic Refrigeration [2] 
temperature liquid is then pumped in to the evaporator.
  This consists of a refrigeration cycle, where heat is removed
5. Methods of Refrigeration [4] [6] from a low-temperature space or source and rejected to a
high-temperature sink with the help of external work, and its
Methods of refrigeration can be classified as; inverse, the thermodynamic power cycle. In the power cycle,
  heat is supplied from a high-temperature source to the
 Non-Cyclic  engine, part of the heat being used to produce work and the
 Cyclic   rest being rejected to a low-temperature sink. This satisfies
 Thermoelectric  the second law of thermodynamics.
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A refrigerationn cycle describbes the changees that take pllace in unttil it starts conndensing, andd then condensses the vapor into
thhe refrigerant as it alternateely absorbs annd rejects heaat as it a liiquid by remooving additional heat at constant pressuree and
ciirculates throough a refriggerator. It is also applied to tem
mperature. Bettween points 4 and 5, the liquid refrigeerant
H
HVACR (HVA ACR (Heatingg, Ventilatingg, Air Conditiioning goees through thhe expansion valve (also called a throttle
& Refrigeratiion) refers to technologgy of indooor or valve) where itss pressure abrruptly decreasses, causing flashf
auutomotive envvironmental comfort)
c workk, when desccribing evaaporation andd auto-refrigerration of, typ pically, less than
thhe "process" of o refrigerant flow throughh an HVACR R unit, half of the liquidd.
w
whether it is a packaged
p or split
s system. Heat
H naturally flows  
frrom hot to coold. Work is applied
a to coool a living spaace or Thaat results in a mixture off liquid and vaporv at a loower
sttorage volumee by pumpingg heat from a lower tempeerature tem
mperature andd pressure as shown at point 5. The cold
heeat source intto a higher teemperature heeat sink. Insuulation liquuid-vapor mixxture then travvels through th
he evaporator coil
(TThermal insullation is the reduction off the effects of o the or tubes and is completely vaporized by cooling
c the warm
w
vaarious processses of heat traansfer betweenn objects in thhermal air (from the spaace being refrrigerated) beinng blown by a fan
coontact or in raange of radiattive influencee) is used to reduce
r acrross the evapoorator coil or ttubes. The ressulting refrigeerant
thhe work and energy requiired to achievve and mainttain a vappor returns to the compresssor inlet at pooint 1 to compplete
loower temperaature in the cooled spacce. The opeerating the thermodynam mic cycle. 
prrinciple of the refrigeeration cyclee was desccribed
m
mathematically y by Sadi Carnnot in 1824 ass a heat enginee. The Thee above disscussion is based on th he ideal vaapor-
m common types of refriggeration systeems use the revverse-
most commpression reffrigeration cyycle, and does not take into
R
Rankin vapor-ccompression refrigeration
r c
cycle. acccount real-worrld effects likee frictional pressure drop inn the
  sysstem, slight thermodynam mic irreversib bility during the
C
Cyclic refrigeraation can be classified
c as:  commpression off the refrigerrant vapor, or o non-ideal gas
1. Vapor cyclee, and behhavior (if any)).
2. Gas cycle  

Vapor cycle refrigeration cann further be cllassified as:

V
1. Vapor-comppression refriggeration
2. Vapor-absoorption refrigeration

5.2.1 Vapor-coompression Cycle 

C
T vapor-com
The mpression cyccle is used in
i most houssehold
reefrigerators as
a well as inn many largee commerciaal and
inndustrial refrrigeration syystems. Figure 1 providdes a
scchematic diaggram of the components
c o a typical vapor-
of v
coompression reefrigeration syystem.
 

 
Figuree 2: Temperatture–Entropy diagram 
d

Herre are the varrious processees of vapor compression

c c
cycle
(reffer the figure)):
 
1) Compression n: The vapoors of refrig gerant enter the
compressor and
a get compressed to high pressure and high h
temperature. During this process thee entropy of the
refrigerant iddeally remainns constant and it leaves in
  superheated state.
s
Figurre 1: Vapor coompression reffrigeration  2) Condensatioon: The superrheated refrig gerant then ennters
  the condenseer where it is cooled eitheer by air or water
w
T thermodynnamics of thhe cycle can be analyzed on a
The due to whicch its tempeerature reducces, but presssure
diiagram as shoown in Figurre 2. In this cycle,
c a circuulating remains constant and it getts converted in
nto liquid state.
reefrigerant suchh as Freon ennters the com
mpressor as a vapor.
v 3) Expansion: The liquid refrigerant then enters the
From point 1 too point 2, the vapor is commpressed at constant expansion valve
v or thrrottling valvee where suddden
enntropy and exits the com mpressor as a vapor at a higher
h expansion off the refrigerrant occurs, due
d to whichh its
teemperature, but
b still beloow the vaporr pressure at that temperature and pressuree falls down.. The refrigeerant
teemperature. From point 2 to t point 3 andd on to point 4, the leaves expannsion valve in partially liquid state and
vaapor travels through
t the coondenser whiich cools the vapor partially in gaaseous state.

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4)) Evaporatioon or coolin ng: The paartially liquidd and a generator whicch, on heat adddition, drives off the refrigeerant
partially gaaseous refrigerant at veryy low tempeerature vappor from the high-pressure
h liquid. Somee work is requuired
enters the evaporator
e whhere the substaance to be coooled is by the liquid pum mp but, for a given quantity y of refrigerannt, it
kept. It is here
h where thee refrigerationn effect is prodduced. is much
m smaller than needed bby the compreessor in the vapor
The refrigerrant absorbs the
t heat from the substancee to be commpression cyccle. In an abssorption refrig gerator, a suittable
cooled and gets converted into vapor state.
s commbination of refrigerant
r annd absorbent isi used. The most m
  commmon combinnations are am mmonia (refrig gerant) and water
w
T
This low pressure refrigerant is then absorbed by the (ab
bsorbent), andd water (refrrigerant) and lithium brom mide
coompressor whhere it is compressed agaain and the whole w [ab
bsorbent].
cyycle of refrigeeration repeatts again. The vapor compreession  
cyyclic process is used for reffrigeration in domestic as well
w as Thee various proocesses of thhe vapor abso orption cycle are
coommercial applications. The orddinary houssehold sim
milar to the one o in vapor compression n cycle, only the
reefrigerator is a good exam mple of the application of o this method of comppression of tthe refrigeran nt is differentt. In
cyycle.  vappor absorptionn system amm monia is used as the refrigerrant,
whhich has very high affinity to dissolve in n water. Heree are
varrious processees of vapor abssorption cyclee:
 
1) Compression
C n or absorptioon of the refrrigerant: In vapor
abssorption system m there is no traditional coompressor, insstead
there is absorberr. The absorbber consists of water, calleed as
abssorbent, in which
w the reffrigerant, amm monia, dissollves.
Thiis mixture off water and aammonia is then t pumped and
heaated thus inccrease in tem mperature and d pressure off the
ammmonia occurs. Ammonia leaves the absorber at high h
preessure and highh temperatture. Some work w has too be
proovided to thee pump and hheating is caarried out byy the
steaam. The amoount of electrricity required d by the pum mp is
muuch lesser thann that requiredd by the comprressor hence there t
is lots of saving of electricity, however, the additional source
of heat
h in the forrm of steam haas to be provid ded. 
 
  2) Condensatiion: The rrefrigerant at a pressure and
5.2.2 Vapor ab bsorption cyccle  mperature thenn enters conddenser wheree it is cooledd by
tem
Inn the early years of thee twentieth century,
c the vapor watter and its temmperature and pressure redu uces. 
abbsorption cycle using wateer-ammonia syystems was poopular 3) Expansion:
E T
Thereafter the expansion of refrigerant occcurs
annd widely used.
u After the
t developm ment of the vapor in throttling
t valvve due to whicch the temperaature and presssure
coompression cyycle, the vapoor absorption cycle lost muuch of of the
t ammonia refrigerant
r redduces drasticaally and suddeenly. 
itts importance because of itss low coefficiient of perform
mance 4) Evaporation:
E : Finally the reefrigerant enteers the evaporrator
(aabout one fiftfth of that off the vapor compression cycle).
c whhere it producees the cooling effect. It leav ves the evaporrator
T
Today, the vappor absorptionn cycle is usedd mainly wherre fuel in vapor
v state annd then enters absorber, wh here it is absorrbed
foor heating is available buut electricity is not, such as in by absorbent, water
w and compressed by the pump. This
reecreational veehicles that carry
c LP gas. It is also ussed in proocess repeats again
a and cyclle continues. 
inndustrial envvironments where plentiful waste heat Theere are differeent types absorbents like waterw and lithhium
ovvercomes its inefficiency. 
i broomide that cann be used witth refrigerant ammonia. Thhese
  sysstems are caalled water aabsorption sy ystem or lithhium
broomide absorptiion system.
 
5.2.3 Gas cycle [3] 
Wh hen the workking fluid is a gas that is compressed and
exppanded but dooesn't change pphase, the refr frigeration cyccle is
callled a gas cyccle. Air is most often this working
w fluidd. As
there is no conddensation and evaporation intended in a gas
cyccle, componeents corresponding to thee condenser and
evaaporator in a vapor
v compresssion cycle are the hot and cold
gass-to-gas heat exchangers
e in gas cycles. 

 
 
T absorptionn cycle is sim
The milar to the compression
c cycle,
exxcept for thhe method of raising thee pressure of o the
reefrigerant vappor. In the abssorption systeem, the compressor
iss replaced by an absorber which
w dissolvees the refrigerrant in
a suitable liquid, a liquid pum
mp which raisses the pressurre and

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  5.4 Magnetic refrigeration [1] [6] 
 
Magnetic refrigeration, or adiabatic demagnetization, is a
cooling technology based on the magnetocaloric effect, an
intrinsic property of magnetic solids. The refrigerant is often
a paramagnetic salt, such as cerium magnesium nitrate. The
active magnetic dipoles in this case are those of the electron
shells of the paramagnetic atoms. 

A strong magnetic field is applied to the refrigerant, forcing

its various magnetic dipoles to align and putting these
degrees of freedom of the refrigerant into a state of lowered
entropy. A heat sink then absorbs the heat released by the
refrigerant due to its loss of entropy. Thermal contact with
the heat sink is then broken so that the system is insulated,
  and the magnetic field is switched off. This increases the
The gas cycle is less efficient than the vapor compression heat capacity of the refrigerant, thus decreasing its
cycle. As such the working fluid does not receive and reject temperature below the temperature of the heat sink. Because
heat at constant temperature. In the gas cycle, the few materials exhibit the required properties at room
refrigeration effect is equal to the product of the specific temperature, applications have so far been limited to
heat of the gas and the rise in temperature of the gas in the cryogenics and research. 
low temperature side. Therefore, for the same cooling load, a
gas refrigeration cycle will require a large mass flow rate
and would be bulky.
 
Because of their lower efficiency and larger bulk, air cycle
coolers are not often used nowadays in terrestrial cooling
devices. The air cycle machine is very common, however,
on gas turbine-powered jet aircraft because compressed air is
readily available from the engines' compressor sections.
These jet aircraft's cooling and ventilation units also serve
the purpose of pressurizing the aircraft.
 
5.3 Thermoelectric refrigeration [1] [6] 
 
Thermoelectric cooling uses the Peltier effect to create a heat
flux between the junctions of two different types of
5.5 Other Methods [1] [6] 
materials. This effect is commonly used in camping and
portable coolers and for cooling electronic components and
Other methods of refrigeration include the:- 
small instruments. 
 
5.5.1)Air cycle machine: - An air cycle machine (ACM) is
the refrigeration unit of the environmental control system
(ECS) used in pressurized gas turbine-powered aircrafts. The
Air Cycle cooling process uses air instead of Freon in a gas
cycle 

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5.5.2) The vortex tube: - It is a mechanical device that flow rate. It is important to note that both Coefficient of
separates a compressed gas into hot and cold streams. It has Performance and Performance Factor for a refrigeration
no parts. It is used for spot cooling, when compressed air is system are only defined at specific operating conditions.
available; and  Moving away from those operating conditions can
  dramatically change a system's performance.
5.5.3) Thermo acoustic refrigeration: - Thermo acoustic  
engines are thermo acoustic devices which use high- 7. Assessment of Refrigeration [4]
amplitude sound waves to pump heat from one place to
another. It is using sound waves in a pressurized gas to drive 7.1 TR
heat transfer and heat exchange. 
TR is the cooling effect produced is quantified as tons of
5.5.4)Steam jet cooling: - Steam jet cooling uses a high- refrigeration, also referred to as “chiller tonnage.
pressure jet of steam to cool water or other fluid media. Its
principle is, steam is passed through a vacuum ejector of § TR = Q x Cp x (Ti – To) / 3024 
high efficiency to exhaust a separate, closed vessel which Where Q is mass flow rate of coolant in kg/hr, Cp is coolant
forms part of a cooling water circuit. The partial vacuum in specific heat in kCal /kg deg C,  Ti is inlet temperature of
the vessel causes some of the water to evaporate, thus giving coolant to evaporator (chiller) in 0C,  To is outlet
up heat through evaporative cooling. The chilled water is temperature of coolant from evaporator (chiller) in 0C. 
pumped through the circuit to air coolers, while the 1 TR of refrigeration = 3024 kCal/hr heat rejected
evaporated water from the ejector is recovered in separate  
condensers and returned to the cooling circuit. Steam jet 7.2 Specific Power Consumption 
cooling experienced a wave of popularity during the early
1930s for air conditioning large buildings. Steam ejector The specific power consumption kW/TR is a useful indicator
refrigeration cycles were later supplanted by systems using of the performance of a refrigeration system. By measuring
mechanical compressors. the refrigeration duty performed in TR and the kW inputs,
kW/TR is used as an energy performance indicator. 
6. Unit of refrigeration [6]
7.3 Coefficient of Performance 
The units of refrigeration are always a unit of power.
Domestic and commercial refrigerators may be rated in kJ/s, The theoretical Coefficient of Performance (Carnot), {COP
or Btu/h of cooling. For commercial and industrial (Carnot), a standard measure of refrigeration efficiency of an
refrigeration systems most of the world uses the kilowatt ideal refrigeration system} depends on two key system
(kW) as the basic unit refrigeration. Typically, commercial temperatures:
and industrial refrigeration systems North America are rated  
in Tons of Refrigeration (TR). Historically, one Ton of Evaporator temperature (Te) and Condenser temperature
Refrigeration was defined as the energy removal rate that (Tc)
will freeze one short ton of water at 0 °C (32 °F) in one day.  
This was very important because many early refrigeration COP is given as: COP (Carnot) = Te / (Tc - Te)
systems were in ice houses. The simple unit allowed owners  
of this refrigeration systems measure a days output of ice This expression also indicates that higher COP (Carnot) is
against energy consumption and compare their plant to one achieved with higher evaporator temperatures and lower
down the street. While ice houses make up a much smaller condenser temperatures. But COP (Carnot) is only a ratio of
part of the refrigeration industry than they once did the unit temperatures, and does not take into account the type of
of Tons of Refrigeration has remained in North America. compressor.
The unit's value as historically defined is approximately  
11,958 BTU/hr (3.505 kW) has been redefined to be exactly
Hence the COP normally used in industry is calculated as
12,000 BTU/hr (3.517 kW). 
follows: 
While not truly a unit, a refrigeration system's Coefficient of
Performance (CoP) is very important in determining a  
system's overall efficiency. It is defined as refrigeration where the cooling effect is the difference in enthalpy across
capacity in kW divided by the energy input in kW. While the evaporator and expressed as kW.
CoP is a very simple measure, like the kW, it is typically not  
used for industrial refrigeration in North America. Owners  
and manufacturers of these systems typically use  
Performance Factor. A system's Performance Factor is  
defined as a system's energy input in horsepower divided by  
its refrigeration capacity in Tons of Refrigeration. Both  
Coefficient of Performance and Performance Factor can be  
applied to either the entire system or to system components.  
For example an individual compressor can be rated by  
looking at the energy required to run the compressor versus  
the expected refrigeration capacity based on inlet volume
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8. Common Refrigerants [7] 1)Type of refrigerant used: In vapor compression cycle
liquids like Freon and ammonia are used as the refrigerant.
There are several fluorocarbon refrigerants that have been In the gas cycle the gas like air is used as the refrigerant.
developed for use in VCRC. 2)Heat exchangers: In the vapor compression refrigeration
  cycle condenser and evaporator are the two heat
Dichlorofluoromethane CCl2F2 R12 exchangers where the refrigerant gives up and absorbs
- used for refrigeration systems at higher       heat respectively. The refrigerant undergoes change in
temperature levels typically, water chillers phase in both the heat exchangers. In the gas cycle the
and air conditioning. refrigerant exchanges heat in the heat exchangers, but
has less chlorine, a little better for the CHClF2 R22 there is no phase change of the gas.
environment than R12 and used for lower 3)Efficiency of the cycle: The efficiency of the vapor
temperature applications compression cycle is more than that of the gas cycle. For
tetrafluorethane - no chlorine ,it went into CFH2CF3 R134a producing the same amount of refrigerating effect in the
production in 1991 and acted as replacement
gas cycle, large volume of gas is required; hence the
for R12
Dichlorofluoroethane C2H3FCl2 R141b systems tend to become very large, bulky and expensive,
corrosive and toxic, used in absorption NH3 Ammonia which are not affordable for the domestic applications.
systems 4)Applications: The vapor compression cycle is most
behaves in the supercritical region, low CO2 R744 widely used for the refrigeration purposes. It is used in
efficiency household refrigerators, air-conditioners, water cooler, ice
Combustible propane R290 and ice cream makers, deep freezers, large industrial
refrigeration and air-conditioning systems, etc. Since the
 
size of the gas compression systems is very large, they are
9. How to Choose a Refrigerant [7] not used for the domestic and industrial purposes. They
are used widely in the aircraft air-conditioning systems
Factors needed to be considered are Ozone Depletion since in aircrafts air at very high pressures is available
Potential,  Global Warming Potential,  Combustibility,  readily and there won’t be the need of air compressors.
Thermal Factors.  This makes the air-conditioning system in the aircraft light
 Ozone Depletion Potential:  these  are  chlorinated and weight and less power consuming. The use of air as the
brominated refrigerants, acts as a catalyst to destroy ozone refrigerant in aircraft prevents the dangers of fire of from
molecules  and reduces the natural shielding effect from the flammable refrigerants.
incoming ultra violet B radiation. 
 Global Warming Potential:  Gases that absorb infrared Differences between an absorption refrigeration system and
energy, with a high number of carbon-fluorine bonds and  a VCRC [4] 
generally have a long atmospheric lifetime.  Absorption RS VCRC
 Combustibility: All hydro-carbon fuels, such as propane   The refrigerant is absorbed by an  Vapour is compressed
 Thermal Factors:-The heat of vaporization of the absorbent material to form a between the evaporator
liquid solution. and the condenser.
refrigerant should be high. The higher h(fg), the greater
the refrigerating effect per kg of fluid circulated. The  Heat is added to the process to  Process is driven by work
retrieve the refrigerant vapour
specific heat of the refrigerant should be low. The lower
from the liquid solution.
the specific heat, the less heat it will pick up for a given
 Process is driven by heat  
change in temperature during the throttling or in flow
through the piping and consequently the greater the  
refrigerating effect per kg of refrigerant.  The specific 10. Current Applications of Refrigeration [6]
volume of the refrigerant should be low to minimize the
work required per kg of refrigerant circulated.  Since Probably the most widely used current applications of
evaporation and condenser temperatures are fixed by the refrigeration are for the refrigeration of foodstuffs in homes,
temperatures of the surroundings. Selection is based on restaurants and large storage warehouses. The use of
the suitability of the pressure-temperature relationship of refrigerators in kitchens for the storage of fruits and
the refrigerant  vegetables has permitted the addition of fresh salads to the
 Other factors include:‐  Chemical Stability,  Toxicity,  modern diet year round, and to store fish and meats safely
Cost, Environmental Friendliness,  Does not result in very for long periods.
low pressures in the evaporator (air leakage), Does not  
result in very high pressures in the condenser (refrigerant In commerce and manufacturing, there are many uses for
leakage)  refrigeration. Refrigeration is used to liquefy gases like
oxygen, nitrogen, propane and methane for example. In
The vapor compression cycle is most commonly used for compressed air purification, it is used to condense water
vapor from compressed air to reduce its moisture content. In
refrigeration.  
Comparison of vapor compression and gas compression oil refineries, chemical plants, and petrochemical plants,
refrigerating cycles based on following parameters: [4] refrigeration is used to maintain certain processes at their
required low temperatures (for example, in the alkylation of
 
butenes and butane to produce a high octane gasoline
component). Metal workers use refrigeration to temper steel
and cutlery. In transporting temperature-sensitive foodstuffs
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Impact Factor (2012): 3.358
and other materials by trucks, trains, airplanes and sea-going
vessels, refrigeration is a necessity. 

Dairy products are constantly in need of refrigeration, and it

was only discovered in the past few decades that eggs
needed to be refrigerated during shipment rather than
waiting to be refrigerated after arrival at the grocery store.
Meats, poultry and fish all must be kept in climate-
controlled environments before being sold. Refrigeration
also helps keep fruits and vegetables edible longer. One of
the most influential uses of refrigeration was in the
development of the sushi/sashimi industry in Japan. Prior to
the discovery of refrigeration, many sushi connoisseurs
suffered great morbidity and mortality from diseases such as
hepatitis A However the dangers of unrefrigerated sashimi
was not brought to light for decades due to the lack of
research and healthcare distribution across rural Japan.
Around mid-century, the Zojirushi Corporation based in
Kyoto made breakthroughs in refrigerator designs making
refrigerators cheaper and more accessible for restaurant
proprietors and the general public. 
 
References
[1] Ameen Ahmadul Refrigeration and Air Conditioning
Prentice Hall of India Pvt. Ltd. Publishing company,
New Delhi
[2] Arora, C.P. Refrigeration and Air Conditioning. Second
edition. Tata McGraw-Hill
[3] Publishing Company Ltd. 2000.
[4] Arora, Ramesh Chandra. "Mechanical vapour
compression refrigeration". Refrigeration and Air
Conditioning. New Delhi, India: PHI Learning
[5] Energy Efficiency Guide for Industry in Asia –
www.energyefficiencyasia.org Copyright © United
Nations Environment Programme (year 2006),
Refrigeration & Air conditioning system
[6] www.honeywell.com/refrigeration, An introduction to
Refrigeration.
[7] http://en.wikipedia.org/wiki/Refrigeration
[8] http://educypedia.karadimov.info/library/c6.pdf 

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