Refrigeration_and_Air_conditioning_03-08-23[1] short.pdf

a precise pdf on refrigeration and air conditioning

1. Welcome
REFRIGERATION
&
AIR CONDITIONING
(PCC-ME –504/21)
5
th
Semester
LTP-3 0 0 Sessional –25 Marks
Credits-03 Theory -75 Marks
Exam Duration: 3 Hours

2. Syllabus Refrigeration
•Pre-Requisite: Thermodynamics
•Successive: Air Conditioning Equipments, Estimation and Design of RAC
Plants
•Course Objectives:
•The objective of studying this course is to describe the refrigerants,
analyze refrigeration systems & various controls, estimation of the heating
& cooling load and design air conditioning systems.
•Course Outcomes (COs): At the end of the course, the student shall be
able to:
•CO 1-Classify the refrigerants and analyze the various conventional
refrigeration systems.
•CO 2-Describe the refrigeration systems other than the conventional
refrigeration systems.
•CO3-Analyze the different psychometric processes & evaluate cooling and
heating loads.
•CO 4-Illustrate the different devices used in RAC systems.

3. Course contents
•Unit 1
•Basic of Refrigeration and Air refrigeration: Methods of refrigeration, Industrial
Refrigeration; Unit of refrigeration; Coefficient of performance (COP) Refrigerants-Definition,
Classification, Nomenclature, Desirable properties, Comparative study, secondary
refrigerants, Introduction to eco-friendly new Refrigerants and their analysis Refrigerants
mixtures: properties and characteristics -Ozone depletion and global warming issues. Air
Refrigeration Systems: Brayton refrigeration or the Bell Coleman air refrigeration cycle; Air-
craft refrigeration systems, Simple cooling and Simple evaporative types, Boot strap and Boot
strap evaporative types, Regenerative type and Reduced Ambient type system, comparison of
different air refrigeration systems, advantages and disadvantages of air refrigeration cycle,
Actual air conditioning system with controls, Numerical Problems (7)
•Unit 2
•VapourCompression Refrigeration: VC cycle on P-V, T-S and PH diagrams; Effects of
operating conditions on COP; Cooling and superheating; Comparison of VC cycle with Air
Refrigeration cycle. Super critical vapourcompression cycle. Multistage VapourCompression
(VC) Refrigeration Systems: Necessity of compound compression, Compound VC cycle,
Multistage compression with flash inter-cooling and / or water inter-cooling; systems with
individual or multiple expansion valves; Production of low temperatures: Introduction to
Cryogenics, Multistage refrigeration system, Two and three stage cascade systems. Numerical
Problems. (7) Course Contents:

4. •Unit 3
•Other Refrigeration Systems: Vapour Absorption Systems, Practical
Ammonia Absorption System, COP of the Absorption System, Lithium
Bromide-Water Absorption Refrigeration Systems and Electrolux
Refrigeration system, Solar energy (Solar Concentrator) based absorption
refrigeration systems, Vapour jet, thermoelectric and Vortex tube
refrigeration, Relative merits and demerits, Applications. (5)
•Unit 4
•Psychometric & Air Conditioning Processes: Properties of moist Air, Gibbs
Dalton law, Specific humidity, Degree of saturation, Relative humidity,
Enthalpy, Humid specific heat, Wet bulb temp., Thermodynamics wet bulb
temp, Psychometric chart; Psychometric of air-conditioning processes,
Psychometric processes in air washer, Numerical Problems. (5)

5. •Unit 5
•Heating and cooling load calculation for HVAC system design: Outside
and inside design conditions; Sources of cooling load and heating load,
Heat transfer through structure, Solar radiation, Electrical appliances,
Infiltration and ventilation, Heat generation inside conditioned space;
Comfort and industrial air conditioning, Load calculations and Heat
pumps, Numerical Problems. (6)
•Unit 6
•Equipment selection for HVAC system: Air distribution system; Basic of
Duct systems design; Filters; Refrigerant piping; Design of summer air-
conditioning and Winter air conditioning systems; Temperature sensors,
Pressure sensors, Humidity sensors, Actuators, Safety controls;
Accessories, Different types of compressor used in refrigeration. (6)

6. •Recommended/ Reference Books:
•1. Refrigeration & Air conditioning –R.C. Jordan and G.B. Priester, Prentice Hall of
India.
•2. Refrigeration & Air conditioning –C.P. Arora, TMH, New Delhi.
•3. A course in Refrigeration & Air Conditioning –Arora & Domkundwar, Dhanpat Rai
& sons.
•4. Refrigeration & Air conditioning –W.F. Stocker and J.W. Jones, TMH, New Delhi.
•5. Refrigeration & Air conditioning-Manohar Prasad Wiley Estern limited, New
Delhi.
•6. Refrigeration and Air Conditioning by D.S.Kumar, S.K.Kataria & Sons, New Delhi

7. Unit 1
•SCIENCE OF PROVIDING AND MAINTAING
THE LOW TEMPERATURE THAN THAT OF
SURROUNDING.
•DEVELOPMENT OF TEMPERATURE
DIFFERANTIALS.
•CONTROLS ONLY TEMPERATURE NOT OTHER
FACTORS LIKE HUMIDITY ETC.
•SCIENCE UTILISES SEVERAL METHODS FOR
LOW TEMPERATURE PRODUCTION.

8. Continued
•Ice Refrigeration
•Evaporative Refrigeration
•Vapor Refrigeration systems
•Vapor Absorption Refrigeration System
•Steam-jet Refrigeration systems
•Refrigeration by Using Liquid Gases
•Dry Ice Refrigeration

9. Unit of Refrigeration
•Mechanical equipment power generally given in
•H.P.
•Electrical power generally given in Kw or MW.
• Similarly unit of Refrigeration is “Ton of Refrigeration”.
• A ton of refrigeration is defined as the quantity of heat required to be removed
from one ton of ice within the 24 hours when the initial condition of water is zero
degrees centigrade, because same cooling effect will be given by melting the same ice
and denoted by TR.
•Hence
• 1x 2,000 lb x144 Btu / lb
•1TR= --------------------------------
• 24 hr
• =12,000 Btu / hr =200 Btu / min
• 12,000Btu/hr
• = --------------≈ 50 kcal/ min
• 3.968
• =12,000x 1.055 kJ =3.517 kW

10. HEAT ENGINE, HEAT PUMP AND REFRIGERATING MACHINE
•Systems having thermodynamic importance
are classified in the two classes:-
•Work developing systems.
All types of engines producing power using
the thermal energy, Heat Engines.
•Work absorbing systems.
Compressors, Refrigerators and Heat pumps

11. COP of Refrigerator
COP= Heat Extracted (Q)/ Work done(W)
Theoretical COP= Q/W
COP=1/Ƞ
COP always >1
Relative COP= Actual COP/ Theoretical
COP

12. Heat Engine, Heat Pump, and Refrigerator 2
12
2
Q
QQ
E
Q
W
SuppliedHeat
DoneW ork
EngineHeat



 12
1
1
QQ
Q
W
Q
C OP
R
re fr ige r ator


 11
Re
12
1
12
22





fr ige r ator
P
PumpHe at
C OP
QQ
Q
QQ
Q
W
Q
EPRorC OP

13. Heat Engine, Heat Pump and refrigerator
•For Heat Pump TS ,i.e. source temperature will be
atmospheric temperature and sink temperature
•TA will be room temperature.
•*Heat pump is a reverse of Refrigerator.
•*Heat pump extract the heat from atmosphere
and supply the same to the space to be heated.
•*All the above cycles are the thermodynamic
systems and based on the reversed carnot cycle
except heat engine which is based on carnot
cycle.

14. Performance of a system:-
•------------------------------------
•Heat supplied by the source = Q
•Temperature of source = TS
•Amount of work done by the engine =W
•Heat rejected by the engine to the sink =q
•Temperature of the sink =TA
η=1-(T
A/T
S)
η=W/Q
Engine
ThentheratioW/Qistheknownastheefficiencyof
Heatenginedenotedby“η”

15. Refrigerator and Heat pump
•*REFRIGERATOR:-
•C.O.P.=Q
1/ W
R
•C.O.P=TS/(TS-TA)
Interest is to maintain the low temperature by extracting the
maximum heat with minimum work input, hence ratio is
known as “co-efficient of performance” C.O.P.
•HEAT PUMP:-Interest is to extract heat from the atmosphere
and supply the same to the space to be heated. QS is heat
supplied to the room.
•COP= Q
2/W
P
•COP=T
A/(T
S-T
A)

17. Eco-friendly Refrigerants

18. History Of Refrigeration
•Refrigeration relates to the cooling of air or liquids, thus providing lower
temperature to preserve food, cool beverages, make ice and for many
other .
•Most evidence indicate that the Chinese were the first to store natural ice
and snow to cool wine and other delicacies.
•Ancient people of India and Egypt cooled liquids in porous earthen jars.
•In 1834, Jacob Perkins, an American, developed a closed refrigeration
system using liquid expansion and then compression to produce cooling.
He used Ether as refrigerant, in a hand-operated compressor, a water-
cooled condenser and an evaporator in liquid cooler.

19. Refrigerantion Principle
•Modern refrigeration and air-conditioning
equipment is dominated by vapour compression
refrigeration technology built upon the
thermodynamic principles of the reverse Carnot
cycle.
•Refrigerant Changes phases during cooling and used
again and again.

20. What is a Refrigerant
•Refrigerants are used as working substances in a Refrigeration
systems.
•Fluids suitable for refrigeration purposes can be classified into
primary and secondary refrigerants.
•Primary refrigerants are those fluids, which are used directly
as working fluids, for example in vapour compression and
vapour absorption refrigeration systems.
•These fluids provide refrigeration by undergoing a phase
change process in the evaporator.
•Secondary refrigerants are those liquids, which are used for
transporting thermal energy from one location to other.
Secondary refrigerants are also known under the name brines
or antifreezes

21. What is ChloroFloroCarcons
•Today’s refrigerants are predominantly from a
group of compounds called halocarbons
(halogenated hydrocarbons) or specifically
fluorocarbons.
•Chlorofluorocarbons were first developed by
General Motor’s researchers in the 1920’s and
commercialized by Dupont as “Freons”.

22. Halocarbon Refrigerants
•Halocarbon Refrigerant are all synthetically
produced and were developed as the Freon
family of refrigerants.
Examples :
–CFC’s : R11, R12, R113, R114, R115

23. Freon Group Refrigerants Application and ODP
Values
Refrigerant AreasofApplication ODP
CFC11(R11)
CFC12(R12
)
CFC13(R13)
CFC113(R113
)
CFC114(R114
)
BlendofR22
and R115
(R502)
Air-conditioningSystemsrangingfrom200to
2000tonsincapacity.Itisusedwherelow
freezingpointandnon-corrosivepropertiesare
important.
Itisusedformostoftheapplications.Air-
conditioningplants,refrigerators,freezers,ice-
creamcabinets,watercoolers,windowair-
conditioners,automobileairconditioners.
Forlowtemprefrigerationupto–90Cin
cascadesystem
Smalltomediumair-conditioningsystemand
industrialcooling
Inhouseholdrefrigeratorsandinlargeindustrial
cooling
Frozenfoodice-creamdisplaycasesand
warehousesandfoodfreezingplants.An
excellentgenerallowtemprefrigerant
1.0
1.0
1.0
1.07
0.8
0.34

24. What is Ozone Layer
•Ozone is an isotope of oxygen with three atoms
instead of normal two. It is naturally occurring gas
which is created by high energy radiation from the
Sun.
•The greatest concentration of ozone are found from
12 km to 50 km above the earth forming a layer in
the stratosphere which is called the ozone layer.
•This layer, which forms a semi-permeable blanket,
protects the earth by reducing the intensity of
harmful ultra-violet (UV) radiation from the sun.

25. Ozone Layer Depletion
•In the early70’s,scientists Sherwood Roland and
Mario Molina at the University of California at Irvine
were the first to discover the loss of ozone in
stratosphere while investigating the ozone layer from
highflying aircraft and spacecraft.
•They postulated the theory that exceptionally stable
chlorine containing fluorocarbons could, overtime,
migrate to the upper reaches of the atmosphere and
be broken by the intense radiation and release
chlorine atoms responsible for catalytic ozone
depletion.

26. OZONE LAYER DEPLETION
•N0RMAL REACTION
•O
2= O + O
•O
2+ O = O
3
•But CFC refrigerants leaked during the manufacturing and normal operation or at
the time of servicing or repair, mix with surrounding air and rise to troposphere
and then into stratosphere due to normal wind or storm. The Ultraviolet rays act
on CFC releasing Cl atom, which retards the normal reaction:
•RETARDED REACTION
•O
3 = O
2+ O
•CCL
2F
2= CCLF
2+ CL
•O
3+ CL = CLO + O
2
•O + CLO = CL + O
2

27. Harmful consequences of ozone
depletion
•For Humans Increase in
•skin cancer
•snow blindness
•cataracts
• Less immunity to
•infectious diseases
•malaria
•herpes
•For plants
•smaller size
•lower yield
•increased toxicity
•altered form
•
•For marine life
•Reduced
•plankton
•juvenile fish
•larval crabs and shrimps

28. MONTREAL PROTOCOL
•SIGNED IN 1987 UNDER THE ‘UNEP’, AFTER MUCH DISCUSSIONS
•MORE THAN 170 COUNTRIES HAVE RATIFIED
•INDIA RATIFIED ON SEPT 17,1992
•ONE OF MOST SUCCESSFUL EXAMPLE OF INTERNATIONAL COOPERATION
IN UN HISTORY

29. Montréal Protocol-Control Schedule
ozone depleting
substance
developed countriesdeveloping countries
CFCs phased out end of
1995
total phase out by
2010
halons phased out end of
1993
total phase out by
2010
HCFCs total phase out by
2020
total phase out by
2040

30. CFC Phase-out in India
•What is to be phased out?
•CFC-11, CFC-12 &CFC-113a.
•How much and when?
•Year1999 22,588 MT
• 2005 11,294 MT
• 2010 o MT
•How to achieve the target?
•Production is controlled through a production quota allocated to each producer
every year. The Ozone Cell conducts audits twice a year to monitor the
production.
•How much has been Phaseout?CFC has been completely phased out as on1st
August, 2008

31. Vapor compression refrigeration
System
•In 1834 an American inventor named Jacob Perkins
obtained the first patent for a vapor-compression
refrigeration system, it used ether in a vapor
compression cycle.
•Joule-Thomson (Kelvin) expansion
•Low pressure (1.5atm) low temperature (-10 to
+15℃) inside
•High pressure (7.5atm) high temperature (+15 to
+40℃) outside

32. Components
•Refrigerant
•Evaporator/Chiller
•Compressor
•Condenser
•Receiver
•Thermostatic
expansion valve (TXV)

33. Circulation of Refrigerant
•Compressor
cold vapor from the evaporator is compressed, raising it temperature and boiling point
adiabatic compression
T, b.p. ~ P
work done on the gas
•Condenser
hot vapor from the compressor condenses outside the cold box, releasing latent heat
isothermal, isobaric condensation (horizontal line on PV diagram)
high temperature
T (hot)
latent heat of vaporization Q(hot)
•Expansionvalve (throttling valve)
hot liquid from the condenser is depressurized, lowering its temperature and boiling point
adiabatic, isochoric expansion (vertical line on PV diagram)
T, b.p. ~ P
no work done W=0
•Evaporator
cold liquid from the expansion valve boils inside the cold box, absorbing latent heat
isothermal, isobaric boiling (horizontal line on PV diagram)
low temperature
T (cold)
latent heat of vaporization Q(cold)

34. Importance of Refrigerant
•The thermodynamic efficiency of a refrigeration system
depends mainly on its operating temperatures.
•However, important practical issues such as the system
design, size, initial and operating costs, safety, reliability, and
serviceability etc. depend very much on the type of
refrigerant selected for a given application.
•Due to several environmental issues such as ozone layer
depletion and global warming and their relation to the various
refrigerants used, the selection of suitable refrigerant has
become one of the most important issues in recent times.

35. Refrigerant selection criteria
•Selection of refrigerant for a particular
application is based on the following
requirements:
–i. Thermodynamic and thermo-physical properties
–ii. Environmental and safety properties
–Iii. Economics

36. Thermodynamic and thermo-physical
properties
•The requirements are:
•a) Suction pressure: At a given evaporator temperature, the saturation
pressure should be above atmospheric for prevention of air or moisture
ingress into the system and ease of leak detection. Higher suction
pressure is better as it leads to smaller compressor displacement
•b) Discharge pressure: At a given condenser temperature, the discharge
pressure should be as small as possible to allow light-weight construction
of compressor, condenser etc.
•c) Pressure ratio: Should be as small as possible for high volumetric
efficiency and low power consumption
•d) Latent heat of vaporization: Should be as large as possible so that the
required mass flow rate per unit cooling capacity will be small

37. Thermodynamic and thermo-physical
properties
•In addition to the above properties; the following properties are also
important:
•e) Isentropic index of compression: Should be as small as possible so that
the temperature rise during compression will be small
•f) Liquid specific heat: Should be small so that degree of subcooling will be
large leading to smaller amount of flash gas at evaporator inlet
•g) Vapour specific heat: Should be large so that the degree of
superheating will be small
•h) Thermal conductivity: Thermal conductivity in both liquid as well as
vapour phase should be high for higher heat transfer coefficients
•i) Viscosity: Viscosity should be small in both liquid and vapour phases for
smaller frictional pressure drops
•The thermodynamic properties are interrelated and mainly depend on
normal boiling point, critical temperature, molecular weight and structure.

38. HalocarbonRefrigerants
•Halocarbon Refrigerant are all synthetically
produced and were developed as the Freon
family of refrigerants.
Examples :
–CFC’s : R11, R12, R113, R114, R115
–HCFC’s : R22, R123
–HFC’s : R134a, R404a, R407C, R410a

39. F Gas Stakeholder Group, 14th October 2009 Slide 39
HFCs
•Remain a popular choice
–especially for R22 phase out
•Good efforts at improving leakage
performance
–e.g. Real Zero project
•Interest in R407A to replace R404A
–50% reduction in GWP

41. HCFC
•Transitional compounds with low ODP
•Partially halogenated compounds of
hydrocarbon
•Remaining hydrogen atom allows Hydrolysis
and can be absorbed.
•R22, R123

42. HCFC
•Production frozen at 1996 level
•35% cut by 2005,65% by 2010
•90% by 2015,100 % by 2030
•10 year grace period for developing countries.

43. R22
•ODP-0.05, GWP-1700
•R22 has 40% more refrigerating capacity
•Higher pressure and discharge temp and not suitable
for low temp application
•Extensively used in commercial air-conditioning and
frozen food storage and display cases

44. HFC
•Zero ODP as no chlorine atom contains only
Hydrogen and Flurodine
•Very small GWP values
•No phase out date in Montreal Protocol
•R134a and R152 a –Very popular refrigerants
•HFC refrigerants are costly refrigerants

45. R134a
•ODP-0, GWP-1300
•Used as a substitute for R12 and to a limited
range for R22
•Good performance in medium and high temp
application
•Toxicity is very low
•Not miscible with mineral oil

46. Hydrocarbon
•Very promising non-halogenated organic compounds
•With no ODP and very small GWP values
•Their efficiency is slightly better than other leading
alternative refrigerants
•They are fully compatible with lubricating oils
conventionally used with CFC12.

47. Hydrocarbon Refrigerants
•Extraordinary reliability-The most convincing argument is the reliability of
the hydrocarbon system because of fewer compressor failures.
•But most of the hydrocarbons are highly flammable and require additional
safety precaution during its use as refrigerants.
•Virtually no refrigerant losses
•Hydrocarbons have been used since the beginning of the century and now
being considered as long term solutions to environmental problems,

48. F Gas Stakeholder Group, 14th October 2009 Slide 48
Hydrocarbons
•Dominant in domestic market like household
refrigerators and freezers
•Growing use in very small commercial systemslike
car air-conditioning system
•Examples: R170, Ethane, C
2H
6
R290 , Propane C
3H
3
R600, Butane, C
4H
10
R600a, Isobutane, C
4H
10
Blends of the above Gases

49. R 600a
•ODP-0,GWP-3
•Higher boiling point hence lower evaporator
pressure
•Discharge temp is lowest
•Very good compatibility with mineral oil

50. Flammability
•Approximate auto ignition temperatures
•R22 630 ºC
•R12 750 ºC
•R134a 740 ºC
•R290 465 ºC
•R600a 470 ºC
•

51. Modifications of Electrical Equipment
•Replaced with solid state equivalents
•Sealed to ensure that any sparks do not come
into contact with leaking gas
•Relocated to a position where the component
would not come into contact with leaking gas

52. Modifications of Electrical Equipment
•Faulty components.
•Poor, corroded, loose, or dirty electrical
connections.
•Missing or broken insulation which could
cause arcing/sparks.
•Friction sparks, like a metal fan blade hitting a
metal enclosure.

53. Carbon Dioxide
•Zero ODP & GWP
•Non Flammable, Non toxic
•Inexpensive and widely available
•Its high operating pressure provides potential for
system size and weight reducing potential.
•Drawbacks:
•Operating pressure (high side) : 80 bars
•Low efficiency

54. Ammonia –A Natural Refrigerant
Ammonia is produced in a natural way by human beings and
animals; 17 grams/day for humans.
Natural production 3000 million tons/year
Production in factories120 million tons/year
Used in refrigeration 6 million tons/year

55. Ammonia as Refrigerant
•ODP = 0
•GWP = 0
•Excellent thermodynamic characteristics: small molecular
mass, large latent heat, large vapour density and excellent
heat transfer characteristics
•High critical temperature (132C) : highly efficient cycles at
high condensing temperatures
•Its smell causes leaks to be detected and fixed before reaching
dangerous concentration
•Relatively Low price

56. Some Drawbacks of Ammonia as
Refrigerant
•Toxic
•Flammable ( 16 –28% concentration )
•Not compatible with copper
•Temperature on discharge side of compressor
is higher compared to other refrigerants

57. Water
•Zero ODP & GWP
•Water as refrigerant is used in absorption
system .New developing technology has
created space for it for use in compression
cycles also.
•But higher than normal working pressure
in the system can be a factor in restricted
use of water as refrigerant

58. Application of New Eco-friendly Refrigerants
•Application HFCs used Possible Eco-friendly refrigerant
•
•Domestic refrigeration R134a,R152a HC600a and blends
•Commercial refrigeration R134a,R404A,R407C HC blends,NH
3,CO
2**
•Cold storage ,food processing
•And industrial refrigeration R134a,R404A,R507A NH
3,HCs,CO
2**
•Unitary air conditioners R410A,R407C CO
2, HC s
•Centralized AC (chillers) R134a,R410A,R407C NH
3,HCs,CO
2,water **
•Transport refrigeration R134a,R404A CO
2,
•Mobile air conditioner R134a CO
2,HCs
•Heat pumps R134a,R152a,R404A NH
3,HCs,CO
2,water **
• R407C,R410A

59. General Safety measures for refrigerating
plants
•Reduction of refrigerant contents:
–Components with reduced contents
–Indirect systems with secondary refrigerant: distinction between
generation and transport of cold
•Scheduled maintenance and leak testing
•Governmental surveillance –Refrigerant Audits for
systems operating with HFC’s. Recovery, Stock of used refrigerants,
Recycling of refrigerants.
•For the Netherlands, the combined measures resulted in a leak rate
reduction of 35% (1995) to 8% (2001) for R22-systems

60. Survey Of Refrigerants
Refrigerant Group Atmospheri
c life
ODP GWP
R11 CFC 130 1 4000
R12 CFC 130 1 8500
R22 HCFC 15 .05 1500
R134a HFC 16 0 1300
R404a HFC 16 0 3260
R410a HFC 16 0 1720
R507 HFC 130 1 3300
R717 NH3 - 0 0
R744 CO
2 - 0 1
R290 HC < 1 0 8
R600a HC < 1 0 8

62. Environmental Effects of
Refrigerants
Global warming :
Refrigerants directly contributing to global warming
when released to the atmosphere
Indirect contribution based on the energy
consumption of among others the compressors ( CO
2
produced by power stations )

63. Conclusions
•In the aftermath of the Montreal protocole HFC’s have
predominantly replaced CFC’s and HCFC’s in RAC equipment.
•Due to their high GWP, HFC’s are not a good replacement
solution.
•The solution are the natural refrigerants :
Ammonia, Hydrocarbons and Carbon dioxide
•System need to have low TEWI factor
•High efficiency with ammonia and lower power consumption
with hydrocarbons

64. T-H diagram for water

68. Refrigerants
A “refrigerant” is nothing but a heat-carrying medium, which absorbs heat from a low
temperature compartment and liberates into environment by executing a simple cycle
(i.e. compression, condensation, expansion and evaporation).
•The natural ice and mixture of ice and salt were first refrigerants
•VCRS has used following as refrigerants during the past
Ether
Ammonia
Sulphur dioxide
Methyl chloride
Carbon dioxide etc
•Presently refrigerants used are
Chlorofluorocarbons (CFCs) Contains atoms of carbon, chlorine, and fluorine
Halo-carbon compounds (Freon family), now phased pout
Hydro-carbon compounds (Ethane, propane etc.)

69. What should be the desirable properties of an ideal
refrigerant?
An ideal refrigerant should have following
properties:-
1. Low boiling point.
2. High latent heat of evaporation.
3. low specific heat.
4. high critical temperature.
5. low specific volume of vapor.
6. Non-corrosive.
7. Non-flammable &non-explosive.
8. non-toxic etc.

70. Classification Of Refrigerants
The refrigerants may be broadly
classified into:-
I. Primary refrigerants
II.. Secondary Refrigerants.
The Primary refrigerants may be
further divided into four
subgroups:
-
1. Halo-carbon refrigerants e.g. R-11,
R-12, R-115 etc.
2. Azeotrope refrigerants e.g. R-500,
R-502 ,R-505 etc.
3. Inorganic refrigerants. e.g. R-717
(ammonia), R-118 (Water)
4. Hydro-carbon refrigerants e.g. R-
170 (ethane) etc.

71. Halo-Carbon Refrigerants/ Compounds/Organic refrigerants
•ASHRAE has identified 42 halo carbon refrigerants, but few are in use.
•These are synthetically produced and were developed as family of Freon
refrigerants and may contain one or more of three halogens-chlorine,
fluorine and bromine.
•Thehalogensare agroupin periodic tableconsisting of five chemically
relatedelements: fluorine(F), chlorine(Cl),bromine(Br),iodine(I),
andastatine(At).
•The name "halogen" means "salt-producing". When halogens react with
metals, they produce a wide range of salts, includingcalcium fluoride,
sodium chloride(common table salt),silver bromideandpotassium iodide.
•Freon is trade mark of E.I. Du Pont De Numours and Co. America.
•Most of halo carbons nowadays are available from other manufactures
under the trade names, such as Genetron, Isotron etc.
•First halo carbon refrigerant R-12 was developed by Dr. Thomas Midgley
in 1930.

73. R11
•Trichlorofluoromethane,also
calledfreon-11,CFC-11,orR-11,is
aCFC.Itisacolorless,faintly
ethereal,stable,nontoxic,non-
flammbleandsweetish-smelling
liquidthatboilsaroundroom
temperature.
•Other names:
Trichlorofluoromethane
Fluorotrichloromethane
Fluorochloroform
Freon 11
CFC 11
R 11
Arcton 9
Freon 11A
Freon 11B
Freon HE
Freon MF
•Now phased out
•Alternate refrigerant: R-123 (HCFC)
Properties
Chemical formula CCl3F
Molar mass 137.36g·mol
−1
Appearance Colorless liquid/gas
Odor nearly odorless
Density 1.494 g/cm
3
Melting point −110.48°C (−166.86°F;
162.67K)
Boiling point 23.77°C (74.79°F;
296.92K)
Solubility in water1.1 g/L (at 20 °C)
Latent heat (at -15OC)195KJ/Kg
Vapor pressure 89 kPa at 20 °C
131 kPa at 30 °C

74. R12
Dichlorodifluoromethane is a colorless gas usually sold under the brand name Freon-12,
and a chlorofluorocarbon halomethane used as a refrigerant and aerosol spray
propellant
The best replacement for R12 is considered to be R-134a. The chemical name of R134a
is tetrafluoroethane and it chemical formula is CF3CH2F.
It is a hydrofluorocarbon (HFC) and has zero ozone depletion causing potential and very
low greenhouse effect.
R-134a is nonflammable and non-explosive and has good chemical stability though it
has some affinity towards moisture.

75. R 22 (Chlorodifluoromethane)
Chlorodifluoromethaneordifluoromonochloromethaneis
ahydrochlorofluorocarbon(HCFC). This colorless gas is better known asHCFC-22,
orR-22, orCHClF.
It is commonly used as apropellantandrefrigerant.
These applications are being phased out indeveloped countriesdue to the
compound'sozone depletion potential(ODP) and highglobal warming potential(GWP),
although global use of R-22 continues to increase because of high demand
indeveloping countries.
R-22 is often used as an alternative to the highly ozone-depletingCFC-11andCFC-12,
because of its relatively low ozone depletion potential of 0.055,among the lowest
forchlorine-containinghaloalkanes.
However, even this lower ozone depletion potential is no longer considered acceptable.

76. R 134a (1,1,1,2-Tetrafluoroethane)
R134a is also known as Tetrafluoroethane (CF3CH2F) from the family of HFC
refrigerant.
With the discovery of the damaging effect of CFCs and HCFCs refrigerants to the ozone
layer, the HFC family of refrigerant has been widely used as their replacement.
It is now being used as a replacement for R-12 CFC refrigerant in the area of centrifugal,
rotary screw, scroll and reciprocating compresssors. It is safe for normal handling as it is
non-toxic, non-flammable and non-corrosive.
Currently it is also being widely used in the air conditioning system in newer automotive
vehicles. The manufacturing industry use it in plastic foam blowing. Pharmaceuticals
industry use it as a propellant.

77. Nomenclature of refrigerants
•The Refrigerants are designated by R
•R is followed by two digits or three digits number, say for example R-11 or R-717
•Two digit number refrigerant is Methane based
•Three digit number refrigerant is Ethane based
•First digit on RHS indicates No. of ‘F’ atoms, denoted by ‘q’
•Second digit from RHS indicates one more than No. of ‘H’ atoms, denoted by ‘n’
•Third digit from RHS indicates one less than No. of ‘C” atoms, denoted by ‘m’
•The general chemical formula for any refrigerant is
•C
mH
nCl
pF
q
•Such that n+p+q=2m+2
•And ‘p’ is no. of Cl atoms
•Refrigerant is designated as R-(m-1)(n+1)(q)

78. Blends & Mixtures
•Limited no of pure refrigerants with low ODP
& GWP values
•To try a mixture of pure refrigerants to meet
specific requirement
•Blends are made up of two or more single
component refrigerants.
•One of two situations will occur, depending on
how strongly the different molecules are
attracted to each other:
•

79. Azeotropic Refrigerants
•Blend behaves like a single component refrigerant.
•Azeotropic mixture is a chemical mixture in which there with liquids having a
constantboiling point.
•This is because the vapour of the liquid mixture has the same composition as the
liquid mixture.
•A stable mixture of two or several refrigerants whose vapour and liquid phases
retain identical compositions over a wide range of temperatures.
•Vapour composition= Liquid composition
•Examples : R-500 : 73.8% R12 and 26.2% R152
R-502 : 8.8% R22 and 51.2% R115
R-503 : 40.1% R23 and 59.9% R13

80. Zeotropic Refrigerants
•Blend that behaves like a mixture of the individual
components.
•Vapour composition≠Liquid composition
•A zeotropic mixture is one whose composition in
liquid phase differs to that in vapour phase.
•Zeotropic refrigerants therefore do not boil at
constant temperatures unlike azeotropic refrigerants.
•Examples :R404a : R125/143a/134a (44%,52%,4%)
R407c : R32/125/134a (23%, 25%, 52%)
R410a : R32/125 (50%, 50%)
R413a : R600a/218/134a (3%, 9%, 88%)

81. Thekey differencebetween azeotropic
and zeotropic mixture is thatdew
pointand bubble point of an
azeotropic mixture intersect whereas
dew point and bubble point of a
zeotropic mixture are distinguishable.
The terms azeotropic and zeotropic
mixtures are highly related to each other
since they have opposite properties to
each other. Therefore, they have
different dew and bubble curve
characteristics as well.
Difference

82. Inorganic Refrigerants
•Were in use before invention of halo carbon
refrigerants, but in still use due to inherent
some properties
•Carbon Dioxide
•Water
•Ammonia
•Air
•Sulphur dioxide

83. Ammonia (R-717)
•Ammonia: Used where toxicity is secondary in reciprocating compressions.
Used in absorption systems. Condensers made of iron or steel as it attacks
the copper and bronze in presence of moisture.
•Poisonous, if large quantity inhaled, lesser quantity irritates, somewhat
flammable, explosive with certain quantity of air, Uses: Cold storages, ice
plant, milk plant, beer manufacture, ice cream manufacture, food freezing
plants etc. ODP = 0
•GWP = 0
•Excellent thermodynamic characteristics: small molecular mass, large
latent heat, large vapour density and excellent heat transfer
characteristics
•High critical temperature (132
O
C) : highly efficient cycles at high
condensing temperatures
•Its smell causes leaks to be detected and fixed before reaching dangerous
concentration
•Relatively Low price

84. Air (R-729)
Air: Dry air used as refrigerant in air crafts
To understand why air refrigeration cycle is used in aviation vehicles / aircraft you need
to understand the advantages of air refrigeration cycle which are
1. The refrigerant used namely air is cheap and easily available.
2. There is no danger of fire or toxic effects due to leakages.
3. The weight to tonne of refrigeration ratio is less as compared to other systems
Air doesn't change it's phase throughout the cycle i.e., remains in gaseous phase,
therefore the heat carrying capacity per kg of air is very small as compared to other
cycle in refrigeration. So it is obsolete and only use in air flight.
Air refrigeration cycle used in aircraft because,
Availability of high pressure air.
Due to light weight and low volume of the equipment.

85. Sulphur dioxide (R-764)
Sulfur dioxideorsulphur dioxide(British English) is thechemical compoundwith the
formulaSO
2.
It is a toxicgasresponsible for the smell of burntmatches.
It is released naturally byvolcanic activityand is produced as a by-product of copper
extraction and the burning offossil fuelscontaminated with sulfur compounds.
This is produced by combustion of sulphur in air.
In formers years , widely used in household and small commercial units.
Boiling point= -10
O
C
h
fg(at -15
O
C)= 396 KJ/kg
Stable refrigerant, Non flammable and non-explosive
Unpleasant and irritating odour
Not injurious to food, used as ripener and preservative of foods
In presence of moisture, it is corrosive

86. Water R-118
Principle use of water is as ice.
Due to high freezing temperature of water can not be used in VCRS.
It is used as refrigerant vapour in some absorption systems.
Steam jet.
Carbon dioxide R-744)
The principle refrigeration use of carbon dioxide is same as that of dry ice.
The boiling point is extremely low (-73.6
O
C).
Due to its high operating pressure, compressor is very small for same RE.
Due to low efficiecy, seldom used in household units. Used in ships.

87. Atranscritical cycleis athermodynamic cyclewhere the working fluid goes through
bothSubcriticalandsupercriticalstates. This is often the case whencarbon dioxide,
CO
2, is therefrigerant.
Transcritical cycle
P-h diagrams: (a)
Subcritical cycle and
(b) Transcritical
cycle.

88. Hal-carbon or
organic
refrigerants
Are chloro-
fluoro
derivatives of
methane and
ethane.
Chloro-fluro-
carbon
Fully
halogenated
with chlorine
atoms in the
molecules
CFC R-11, R-11, R-
113, R-114
and R-115
Hydro-chloro-
fluoro-carbon
Contains
hydrogen
atom
HCFC R-22, R-123
Hydro-fluoro-
carbon
Contain no
chlorine atom
HFC R-134a, R-
152a
HydrocarbonContain no
chlorine and
fluorine
atoms
HC R-290, R-600a
Brief about Refrigerants

89. Presence of fluorine atom in molecule of refrigerant makes them physiologically more
favourable.
Cl atom is responsible for depletion of ozone layer. CFCs are more responsible. Have
highest ODP. Also responsible for Global warming.
Ozone layer depletion (ODP)
One Cl atom can destroy 10
5
molecules of ozone.
Relative ability of a substance to deplete the ozone layer is called ODP.
CFCs are worst and their ODP=1
HCFC have relatively low ODP, R-22=0.05, R-123=0.02
HFC do not cause any ozone depletion, R-134a=0
Montreal Protocol, 1987, India became part in 1992.
Global warming potential (GWP)
Global warming means the increase in average temperature of earth.
Causes are increase in CO
2concentration, NO
2emission and use of CFC refrigerants.
The ability of a substance to contribute to global warming is measured by the global
warming potential (GWP).
Some halocarbon have a very high GWP. For example R-22=100 CO
2=1

90. • SIGNED IN 1987 UNDER THE ‘UNEP’, AFTER MUCH DISCUSSIONS
• MORE THAN 170 COUNTRIES HAVE RATIFIED
• INDIA RATIFIED ON SEPT 17,1992
• ONE OF MOST SUCCESSFUL EXAMPLE OF INTERNATIONAL COOPERATION IN
UN HISTORY
MONTREAL PROTOCOL
Montréal Protocol-Control Schedule
ozone
depleting
substance
developed
countries
developing
countries
CFCs phased out
end of 1995
total phase
out by 2010
halons phased out
end of 1993
total phase
out by 2010
HCFCs total phase
out by 2020
total phase
out by 2040

91. ECO-FRIENDLY REFRIGERANTSHCFC
R22,R124
HFC
R134a,R152a
NATURAL REFRIGERANT
NH3, HC'S
CFC
ALTERNATIVES.

92. Environmental and safety properties
•At present the environment friendliness of the refrigerant is a
major factor in deciding the usefulness of a particular
refrigerant. The important environmental and safety
properties are:
•a) Ozone Depletion Potential (ODP): According to the
Montreal protocol, the ODP of refrigerants should be zero,
i.e., they should be non-ozone depleting substances.
Refrigerants having non-zero ODP have either already been
phased-out (e.g. R 11, R 12) or will be phased-out in near-
future(e.g. R22). Since ODP depends mainly on the presence
of chlorine or bromine in the molecules, refrigerants having
either chlorine (i.e., CFCs and HCFCs) or bromine cannot be
used under the new regulations

93. Environmental Effects of
Refrigerants
Global warming :
Refrigerants directly contributing to global warming
when released to the atmosphere
Indirect contribution based on the energy
consumption of among others the compressors ( CO
2
produced by power stations )

94. Environmental and safety properties
•b) Global Warming Potential (GWP): Refrigerants should have
as low a GWP value as possible to minimize the problem of
global warming. Refrigerants with zero ODP but a high value
of GWP (e.g. R134a) are likely to be regulated in future.
•c) Total Equivalent Warming Index (TEWI): The factor TEWI
considers both direct (due to release into atmosphere) and
indirect (through energy consumption) contributions of
refrigerants to global warming. Naturally, refrigerants with as
a low a value of TEWI are preferable from global warming
point of view.

95. Environmental and safety properties
•d) Toxicity: Ideally, refrigerants used in a refrigeration system should be non-toxic.
Toxicity is a relative term, which becomes meaningful only when the degree of
concentration and time of exposure required to produce harmful effects are
specified. Some fluids are toxic even in small concentrations. Some fluids are
mildly toxic, i.e., they are dangerous only when the concentration is large and
duration of exposure is long. In general the degree of hazard depends on:
–-Amount of refrigerant used vs total space
–-Type of occupancy
–-Presence of open flames
–-Odor of refrigerant, and
–-Maintenance condition

96. Environmental and safety properties
•e) Flammability: The refrigerants should preferably be non-
flammable and non-explosive. For flammable refrigerants
special precautions should be taken to avoid accidents.
•f) Chemical stability: The refrigerants should be chemically
stable as long as they are inside the refrigeration system.
•g) Compatibility with common materials of construction (both
metals and non-metals)
•h) Miscibility with lubricating oils: Oil separators have to be
used if the refrigerant is not miscible with lubricating oil (e.g.
ammonia). Refrigerants that are completely miscible with oils
are easier to handle(R12).

97. Environmental and safety properties
•Ease of leak detection: In the event of leakage
of refrigerant from the system, it should be
easy to detect the leaks.
Economic properties:
•The refrigerant used should preferably be
inexpensive and easily available.

98. Classification of refrigerants
Refrigerant
Number
Name Composition or chemical
formula
Safety classification
(mass percentage)
INORGANIC COMPOUND
R-717 ammonia NH
3 B2
R-718 water H
2O A1
R-744 carbon dioxide CO
2 A1
ORGANIC COMPOUND
Hydrocarbons
R-290 propane CH
3CH
2CH
3 A3
R-600 butane CH
3CH
2CH
2CH
3 A3
R-600a isobutane CH(CH
3)
2CH
3 A3
R-1270 propylene CH
3CH=CH
2 A3
Hydrofluorocarbons(HFCs)
R-32 difluoromethane CH
2F
2 A2
R-125 pentafluoroethane CHF
2CF
3 A1
R-134a 1,1,1,2-tetrafluoroethane CH
2FCF
3 A1
R-143a 1,1,1-trifluoroethane CH
3CF
3 A2
R-152a 1,1-difluoroethane CH
3CHF
2 A2
Azeotropic mixtures
R-502 R22/R115 (48.8/51.2) A1
R-507 R125/R143a (50/50) A1
Zeotropic mixtures
R-404A R125/R143a/R134a
(44/52/4)
A1
R-407C R32/R125/R134a
(23/25/52)
A1
R-410A R32/R125 (50/50) A1

99. Type Profile Application
R-134aReplace R-12 in most applications. Good performance in medium temperature
applications ; household refrigerators; car air
conditioning systems; heat pumps; chillers;
transport refrigeration; commercial cooling.
R-245faReplacement of R-123. Chillers, heat transfer fluid.
R-404ANear azeotropic refrigerant containing R-125,
R-143a and R-134a (44/52/4% by weight).
Cold-storage cells; supermarket display cases;
ice machines; replacement for R-502 in
transport refrigeration; retrofit of existing R-
502-installations
R-407AZeotropic refrigerant containing R-32, R-125
and R-134a (20/40/40 weight-%).
Close replacement of R-22 in commercial
refrigeration applications.Possible
replacement for R-404A in supermarket chill
and low temperature systems.
R-407CZeotropic refrigerant containing R-32, R-125
and R-134a (23/25/52 weight-%).
New air-conditioning units or replacement for
R-22 in existing installations; heat-pumps;
industrial and commercial cooling.
Designation and safety classification of refrigerants

100. continued
R-407FZeotropic refrigerant containing R-32, R-125
and R-134a (30/30/40 weight-%).
Close replacement of R-22 in commercial
refrigeration applications. Possible
replacement for R-404A in supermarket
medium and low temperature systems.
R-410ANear azeotropic refrigerant containing R-32
and R-125 (50/50 by weight).
Substitute for R-22 ; air-conditioning units;
heat pumps; cold storage; industrial and
commercial refrigeration; substitution of R-
13B1 in low temperature application
R-417BContains R-125, R-134a and Butane R-600
(79/18.25/2.75 weight-%).
R-22 substitute.
R-422AContains R-125, R-134a and IsobutaneR-600a
(85.1/11.5/3.4 weight-%).
R404A replacement very similar properties;
R502 retrofit refrigerant.
R-422DContains R-125, R-134a and Isobutane R-600a
(65.1/31.5/3.4 weight-%).
R-22 substitue.
R-427AContains R-32, R-125, R-134a and R-143a
(15/25/50/10 weight-%).
R-22 subsitute.
R-507Azeotropic refrigerant containing R-125 and
R-143a (50/50% by weight).
Cold-storage cells; supermarket display cases;
ice machines; replacement for R-502 in
refrigerated transport; replacement for R-502;
retrofit of existing R-502-installations.

101. Refrigeration Application
RefrigerationapplicationShort description
Typical HFCs used
Domestic Refrigeration
Appliances used for keeping food in
dwelling units.
HFC-134a
Commercial Refrigeration
Holding and displaying frozen and
fresh food in retail outlets
R 404A, R 507, HFC-134a
Food Processing and Cold
Storage
Equipment to preserve, process and
store food from its source to the
wholesale distribution point
R410A, R407C, R 507, HFC-134a
Industrial Refrigeration
Large equipment, typically 25 kW to
30 MW, used for chemical processing,
cold storage, food processing and
district heating and cooling
HFC-134a, R-404A, R-507
Transport Refrigeration
Equipment to preserve and store
goods, primarily foodstuffs, during
transport by road, rail, air and sea
R410A, R407C, HFC-134a

102. Eco-friendly refrigerants
Chlorofluorocarbons (CFCs)
These are refrigerants that contain Chlorine, Fluorine and Carbon. They were developed
in the 1930's and were used in a variety of industrial, commercial, household and
automotive applications. They were ideal for commercial, household, and automotive
use due to the fact that they are non-toxic, non-flammable, and non-reactive with other
chemical compounds. In 1973 however, it was discovered that the Chlorine atom in the
CFC's unfortunately is a catalyst for ozone depletion. Basically the Cl atom rips away the
extra oxygen atom in the ozone compound. Since 1987 their use has been prohibited by
the Montreal Protocol.
Hydrochlorofluorocarbons (HCFCs)
These are refrigerants that contain Hydrogen, Chlorine, Fluorine, and Carbon. They
have only about 10% of the ozone depleting potential as CFCs. They are energy-
efficient, low-in-toxicity, cost effective and can be used safely. They have allowed the
CFCs consumption of the world to fall by about 75%. Unfortunately HCFCs are Green
house gases,despite their very low atmospheric concentrations

103. Hydrofluorocarbons (HFC's).
These are refrigerants containing Hydrogen, Fluorine, and Carbon. Therefore they do
not contain any ozone depleting Chlorine. Besides containing no ozone depleting
elements they usually have an even lower global warming potential than HCFCs.
Unfortunately they are targets of the Kyoto_Protocolbecause they have activity in an
entirely different realm of greenhouse gases.

104. Retofitting
Retrofittingrefers to the addition of new technology or features to older systems, for
example:
Power plantretrofit, improving power plant efficiency / increasing output / reducing
emissions,
Home energy retrofit, the improving of existing buildings withenerg
efficiencyequipment,
Seismic retrofit, the process of strengthening older buildings in order to make them
earthquake-resistant,
Refrigeration equipments by introducing to them new refrigerants.
Benefits of a retrofit:
Saving oncapital expenditurewhile benefiting from new technologies,
Optimization of existing plant components,
Adaptation of the plant for new or changed products,
Increase in piece number and cycle time,
Guaranteed spare parts availability
Reduced maintenance costs and increased reliability

105. Cryogenics
Cryogenicrefrigeration systems are different from the refrigeration equipment we
encounter in our everyday environment. Therefrigerantsused incryogenicsystems
are often helium (He), hydrogen (H2), or nitrogen (N2)
The International Congress of Refrigeration endorsed a universal definition of
“cryogenics” and “cryogenic” by accepting a threshold of 120 K (or –153 °C) to
distinguish these terms from the conventional refrigeration.
This is a logical dividing line, since the normalboiling pointsof the so-called
permanentgases(such ashelium,hydrogen,neon,nitrogen,oxygen, and normalair)
lie below −120°C.
While theFreonrefrigerants,hydrocarbons, and other common refrigerants have
boiling points above −120°C.
The U.S.National Institute of Standards and Technologyconsiders the field of
cryogenics as that involving temperatures below −180°C (93K; −292°F).
The term "high temperature cryogenic" describes temperatures ranging from above the
boiling point of liquid nitrogen, −195.79°C (77.36K; −320.42°F), up to −50°C (223K;
−58°F).

106. Carnot Refrigerator
•Reversed cycle is used in refrigeration of Carnot heat engines.
•Purely theoretical concept ever to be achieved in practice.
•Refrigerator based on this cycle is a standard of perfection.

107. Carnot cycle consists of all reversible processes so that this is Reversible
cycle.
In a cyclic process
WQ
W (net work done)
QW
Heat rejected-Heat absorbed= R
Q A
Q  2
T   
12112
ssTss   
1212
ssTT  -
=
COP  
  
1212
121
ssTT
ssT
W
Q
A


 12
12
1
... TthangreaterTWhere
TT
T
POC



108. Discussion
•A high COP is desirable.
•Lower T2, higher the COP.
•higher the T1, higher the COP.
•Lowerthe temperature difference, higher the
COP.
•COP inversely proportional to T-S diagram.
•COP in winter> COP in summer for same
temperature to be maintained.
•COP CARNOT REFRIGERATOR < COP CARNOT A.C

109. Problem
•A cold storage plant is required to store 20 tonnes of
fish. The fish is supplied at a temperature of 30°C. The
specific heat of fish above freezing point is 2.93 kJlkg K.
The specific heat of fish below freezing point is 1.26
kJlkg K. The fish is stored in cold storage which is
maintained at -8°C. The freezing point of fish is -4°C.
The latent heat of fish is 235 kJlkg. If the plant requires
75 kW to drive it, find:
1.The capacity of the plant, and
2.Time taken to achieve cooling. Assume actual C.O.P. of
the plant as 0.3 of the Carnot C.O.P

110. Solution
Actual COP=0.3x6.97=2.091
Find the heat removed from above
equation
Find the capacity of the plant in TR
(1TR=210 kJ/min)

111. Bell-Coleman air Refrigerator arrangement 1

112. Bell-Coleman air Refrigerator
arrangement 2

113. Bell-Colemen Cycle on PV and TS Diagram

114. Bell-Coleman Cycle analysis
•Modification over the carnot cycle.
•*Isothermal processes are replaced by the
•constant pressure processes.
•Let T1, T2,T3,and T4 are the absolute temperatures at the points 1,2,3
and 4 shown in figure.
•Heat abstracted from cold chamber Per kg of air
• qA= CP(T1-T4)………………………………(1)
•Heat rejected by the condenser per kg of air
• qR=CP(T3-T2) ……………………………….(2)
•Work done on the system, w= qR -qA
•W= CP(T3-T2)-CP(T1-T4) per kg of air………

115. Continued
•_)5...(........................................
4
31
2
4
3
1
4
3
1
1
2
1
2
same,
is cylinders both thein n compressio andexpansion of ratio The
)4..(..............................
4131
41
4132
41
w
A
q
COP Thus
T
TT
T
T
T
p
p
p
p
T
T
TTTT
TT
TT
P
CTT
P
C
TT
P
C





















































































116. Continued
•-)7......(....................
1
1
1
1
1
1
2
1
)6.......(
43
4
1
4
3
1
4141
4
3
41
4
T-
1
T
4
T
3
T
1
T
4
T
1
T
COP










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p
r
p
p
TT
T
T
T
TTTT
T
T
TT

117. Continued
•where(consant) c
n
pv law the
following and isentropic theas expansions andn compressio
assuming ,ly respective ratio pressure and re temperatuof terms
in the cycleBeleman theof COP therepresents , (7) and (6)
equations and ratio,expansion or n compressio
4
3
1
2


p
p
p
p
p
r
If the expansion and compression are polytropic and follow the law
pv
n
= C (constant)
,then COP of the cycle is given by following derived the relation,

118. Bell-Colemen Cycle

119. Bell-Colemen Cycle

120. Bell-Colemen Cycle

121. Bell-Colemen Cycle
•If the carnot cycle is used thenT
4=T
1, and this is the source temperature
to be maintained in the refrigerator.
•Similarly T
2=T
3, if the Bell-Colemen cycle is used as carnot refrigerator
,then T
2=T
3as the sink temperature for carnot refrigerator,
•Then COP= ………..8 12
1
TT
T

Where ,
T
1= Temperature to be maintained in the refrigerator and ,
T
2= Atmosphere temperature.
Comparing the eq.(6) and eq.(8)
COP carnot > COP Bell-Coleman
As T
2>T
3

122. Problem
•The atmospheric air at pressure 1 bar and temperature -5°C is
drawn in the cylinder of the compressor of a Bell-Coleman
refrigerating machine. It is compressed isentropically to a
pressure of 5 bar. In the cooler, the compressed air is cooled to
15°C, pressure remaining the same. It is then expanded to a
pressure of 1 bar in an expansion cylinder, from here it is
passed to the cold chamber.
•Find: 1. the work done per kg of air, and 2. C.O.P. of the 'ant.
•For air assume law for expansion, pv
1.2
= constant,' law for
compression, pV
1.2
= constant ld specific heat of air at
constant pressure = 1 kJlkg K.

123. A refrigerating machine o f 6 tonnes capacity working on
Bell-Coleman cycle has an upper limit o f pressure o f 5.2 bar.
The pressure and temperature at the start of compression are 1
bar and 16°C respectively. The compressed air is cooled at
constant pressure to a temperature o f 41°C, enters the
expansion cylinder. Assuming both expansion and compression
processes to be isentropic with y = 1.4, Calculate :
1. Coefficient o f performance;
2. Quantity o f air in circulation per minute;
3. Piston displacement o f compressor and expander;
4. Bore o f compressor and expansion cylinders. The unit runs at
240 r.p.m. and is double acting. Stroke length is 200 mm ; and
5. Power required to drive the unit.
For air, take y = 1.4, and cp = 1.003 kJ/kg K.

124. METHODS OF AIR REFRIGERATION SYSTEM
•Selection Of Refrigeration System For
Air Craft The advent of high-speed passenger aircraft, jet aircraft and
missiles has introduced the need for compact, lightweight and
simple refrigeration system. Air cycle refrigeration systems are
employed for air conditioning the cockpit and cabin space of an
airplane.
Necessitaty of air cooling
•Think about it-
(Q) Can you imagine how many tons of refrigeration is required for an ordinary
passenger aircraft?
(Ans) An ordinary 15 seater plane requires a cooling system capable of 8 TR
capacity.
(Q) Do missile system needs refrigeration system?
(Ans) Yes, to dissipate heat from 10 kw of electronic equipment in missile,
approximately 3 TR of cooling capacity is required

125. METHODS OF AIR REFRIGERATION SYSTEM
•Methods of Air Refrigeration System
•1. Simple air-cooling system.
•2. Simple air evaporative cooling system.
•3. Boot-strap air cooling system.
•4. Boot-Strap air evaporative cooling system.
•5. Reduced ambient air-cooling system.
•6. Regenerative air-cooling system.
•All above cycles are used while plane is on flight whereas during parking
,pre conditioned air is used for cooling.

126. Simple Air-cooling System

127. Simple Air-cooling System
•The various process are discussed below: -
(1) Ramming Process-The ambient air is rammed isentropically from
p1&T1 to p2 &T2.This ideal ramming is shown by Process1-2.Actual
ramming process is shown by curve 1-2’ which is adiabatic not
isentropic.(because of friction).
(2) Compression Process-The isentropic compression of air in the main
compressor is represented by line 2’-3.In actual practice, due to
irreversibilities (because of friction etc.) is represented by curve 2’-3’.
(3) Cooling Process-The compressed air is cooled by the ram air in the
heat exchanger, shown by curve 3’-4.
(4) Expansion Process-The cooled air now expanded isentropically in the
cooling turbine as shown by curve 4-5.In actual practice, because of
irreversibility due to friction etc, the actual expansion is shown by 4-5’.
(5) Refrigeration Process-(5’-6) -The air from cooling turbine (i.e. after
expansion) is sent to the cabin & cockpit where this cold air absorbs
heat thereby producing cooling effect in the cabin.

128. Simple air cooling

129. Simple Air-cooling System

130. Simple air cooling system

131. Simple Air Cooling System

132. Simple Air Evaporative Cooling System

133. Simple Air Cooling System

134. Simple Air Cooling System
•A simple air cooled system is used for an aeroplane having a
load of 10 tonnes. The atmospheric pressure and temperature
are 0.9 bar and 10
0
C respectively. The pressure increases to
1.013 bar due to ramming. The temperature of the air is
reduced by 50
0
C in the heat exchanger. The pressure in the
cabin is 1.01 bar and the temperature of air leaving the cabin is
25°C. Determine:
1 Power required to take the load of cooling in the cabin; and
2. C.O.P. of the system.
Assume that all the expansions and compressions are isentropic.
The pressure of the compressed air is 3.5 bar.

135. Simple evaporative cooling system

136. Simple evaporative cooling system

137. Simple evaporative cooling system
•A simple evaporative air refrigeration system is used for an aeroplane
to 20 tonnes of refrigeration load. The ambient air conditions are 20°C
and 0.9 bar. The ambie~ is rammed isentropically to a pressure of 1 bar.
The air leaving the main compressor at pre! 3.5 bar is first cooled in the
heat exchanger having effectiveness of 0.6 and then in the evapOl
where its temperature is reduced by 5°C. The air from the evaporator is
passed through cooling turbine and then it is supplied to the cabin
which is to be maintained at a temperatw 25°C and at a pressure of
1.05 bar. If the internal efficiency of the compressor is 80% and tlu
cooling turbine is 75% ,determine:
1. Mass of air bled off the main compressor; 2. Power required for the
refrigerating syst and 3. C.O.P. of the refrigerating system.

138. Boot Strap Air Cooling

139. Boot Strap Air Cooling

140. Boot Strap Air Cooling

141. Boot Strap Air Cooling
•A boot-strap cooling system of 10 TR capacity is used in an aeroplane.
The ambient air temperature and pressure are 20°C and 0.85 bar
respectively. The pressure of air increases from 0.85 bar to 1 bar due to
ramming action of air. The pressure of air discharged from the main
compressor is 3 bar. The discharge pressu!e of air from the auxiliary
compressor is 4 bar. The isentropic efficiency ;f each of the compressor
is 80%, while that of turbine is 85%. 50% of the enthalpy of air
discharged from the main compressor is removed In the first heat
exchanger and 30% of the enthalpy of air discharged from the auxiliqry
compressor is removed in the second heat exchanger using rammed air.
Assuming ramming action to be isentropic, the required cabin pressure
of 0.9 bar and temperature of the air leaving the cabin not more than
20°C, find: 1. the power required to operate the system; and 2. the
C.O.P of the system. Draw the schematic and temperature -entropy
diagram of the system. Take 'Y = 1.4 and cp = 1 kJ/kg K.

142. Boot Strap air evaporative cooling system

143. Boot Strap air evaporative cooling system

144. Boot Strap air evaporative cooling system

145. Boot Strap with evaporation
•The following data refer to a boot strap air cycle evaporative refrigeration
•system used for an aeroplane to take 20 tonnes of refrigeration load:
• Ambient air temperature = 15°C
• Ambient air pressure = 0.8 bar
• Mach number of the flight = 1.2
• Ram efficiency = 90%
• Pressure of air bled off the main compressor = 4 bar
• Pressure of air in the secondary compressor = 5 bar
• Isentropic efficiency of the main compressor = 90%
• Isentropic efficiency of the secondary compressor = 80%
• Isentropic efficiency of the cooling turbine = 80%
• Temperature of air leaving the first heat exchanger = 170°C
• Temperature of air leaving the second heat exchanger = 155°C
• Temperature of air leaving the evaporator = 100°C
• Cabin temperature = 25°C
• Cabin pressure = 1 bar
•Find: 1. Mass of air required to take the cabin load, 2. Power required for the refrigeration system,
and 3. C.O.P. of the system.

146. Reduced Ambient Air Cooling System

147. Reduced Ambient Air Cooling System

148. Reduced Ambient Air Cooling System

149. Reduced Ambient Air Cooling System

150. Regenerativeair cooling system

151. Regenerativeair cooling system

152. Regenerativeair cooling system

153. Regenerativeair cooling system

154. Regenerativeair cooling system

155. Vapour Compression Refrigeration
System
•Following are the advantages and disadvantages of the
vapour compression refrigeration system over air
refrigeration system :
•Advantages
•It has smaller size for the given capacity of refrigeration.
•It has less running cost.
•It can be employed over a large range of temperatures.
•The coefficient of performance is quite high.
VCRS was first developed by Jacob Perkins using
hand operation in 1834.

156. VCRS
•Disadvantages
•The initial cost is high.
•The prevention of leakage of the refrigerant
is the major problem in vapour compression
system.

157. Mechanism of a Simple Vapour Compression Refrigeration
System

158. Pressure-Enthalpy (p-h) Chart

159. Ph Chart for R-134a

160. Ph Chart for Ammonia

161. Ph chart for CO
2

162. Thermodynamic Properties for R 134a

163. Types of VCR Cycles
•Cycle with dry saturated vapour after
compression,
•Cycle with wet vapour after compression,
•Cycle with superheated vapour after
compression,
•Cycle with superheated vapour before
compression, and
•Cycle with undercooling or subcooling of
refrigerant.

164. Cycle with dry saturated vapour after compression,

165. Cycle with wet vapour after compression

166. Cycle with superheated vapour after compression

167. Cycle with superheated vapour before compression

168. Cycle with undercooling or subcooling

169. Effect of Condenser Temp on COP

170. Effect of Evaporator Temp. on COP

172. Multistage compression
•Following are the main advantages of compound or multi-stage
compression over single stage compression :
•The work done per kg of refrigerant is reduced in compound
compression with intercooler as compared to single stage compression
for the same delivery pressure.
•It improves the volumetric efficiency for the given pressure ratio.
•The sizes of the two cylinders (i.e. high pressure and low pressure) may
be adjusted to suit the volume and pressure of the refrigerant.
•It reduces the leakage loss considerably.
•It gives more uniform torque, and hence a smaller size flywheel is
needed.
•It provides effective lubrication because of lower temperature range.
•It reduces the cost of compressor.

173. Compound Vapour Compression with Intercooler
•In compound compression vapour
refrigeration systems, the superheated vapour
refrigerant leaving the first stage of
compression is cooled by suitable method
before being fed to the second stage of
compression and so on. Such type of cooling
the refrigerant is called intercooling.

174. Symbols

175. Types of compound compression with intercoolers
1.Two stage compression with liquid intercooler.
2.Two stage compression with water intercooler.
3.’Two stage compression with water intercooler, liquid
subcoo1er and liquid flash chamber.
4.Two stage compression with water intercooler, liquid
subcooler and flash intercooler.
5.Three stage compression with flash chambers.
6.Three stage compression with water intercoolers.
7. Three stage compression with flash intercoolers.

176. 1.Two stage compression with liquid intercooler

177. 1.Two stage compression with liquid intercooler

178. Mass Calculation

179. Two stage compression with liquid intercooler

180. Problem
•Example . Calculate the power needed to
compress 20 kg/min of ammonia saturated
vapour at 1.4 bar to a condensing pressure of
10 bar by two-stage compression with
intercooling by liquid refrigerant at 4 bar.
Assume saturated liquid to leave the
condenser and dry saturated vapors to leave
the evaporator. Use the p-h chart.
•Determine, also, the power needed when
intercooling is not employed.
•Ans: Power needed=86.5 with intercooling
•Power needed = 92 kW without inercooling

181. Solution

182. Problem
•Calculate the power needed to compress 20
kg/min of R-12 from saturated vapour at 1.4
bar to a condensing pressure of 10 bar by two-
stage compression with intercooling by liquid
refrigerant at 4 bar. Assume saturated liquid
to leave the condenser and dry saturated
vapours to leave the evaporator.'
•Use the p-h chart. Sketch the cycle on a
skeleton p-h chart and label the values of
enthalpy at salient points.

183. Two Stage Compression with Water Intercooler and Liquid Sub-cooler

184. Two Stage Compression with Water Intercooler and Liquid Sub-cooler

185. Two Stage Compression with Water Intercooler and Liquid Sub-cooler
•It may be noted that water intercooling reduces the work
to be done in high pressure compressor.
•It also reduces the specific volume of the refrigerant
which requires a compressor of less capacity (or stroke
volume).
•The complete desuperheating of the vapour refrigerant is
not possible in case of water intercooling. It is due to the
fact that temperature of the cooling water used in the
water intercooler is not available sufficiently low so as to
desuperheat the vapour completely

186. Two Stage Compression with Water Intercooler and Liquid Sub-cooler

187. Two Stage Compression with Water Intercooler, Liquid , Sub-cooler and Liquid Flash
Chamber

188. Two Stage Compression with Water Intercooler, Liquid , Sub-cooler and
Liquid Flash Chamber

189. Two Stage Compression with Water Intercooler, Liquid , Sub-cooler and
Liquid Flash Chamber

190. Two Stage Compression with Water Intercooler, Liquid , Sub-cooler and
Liquid Flash Chamber

191. Two Stage Compression with Water Intercooler, Liquid , Sub-cooler and
Liquid Flash Chamber

192. Two stage compression with water intercooler, liquid subcooler and flash intercooler
•m1 flows----10-1-2-3-9-010 and m2 flows----4-5-6-7-8-4

193. Two stage compression with water intercooler, liquid subcooler and flash
intercooler

194. Two stage compression with water intercooler, liquid subcooler and flash
intercooler

195. Two stage compression with water intercooler, liquid subcooler and flash
intercooler

196. Three stage compression with water intercooler

197. Three Stage compression with water intercoolers

198. Three stage compression with flash chambers

199. Three stage compression with flash chambers

200. Three stage compression with flash Intercoolers

201. Three stage compression with flash Intercoolers

202. Three Stage compression with multiple expansion valves and
flash intercoolers

203. Three Stage compression with multiple expansion valves and
flash intercoolers

204. Problem

205. Solution

206. Solution of problem on P-H Chart for Ammonia

207. Vapour Absorption
Refrigeration System

208. Vapour Absorption Refrigeration System(VARS)
•VARSisoldestone.
•PrincipalofVARSwasfirst
discoveredbyMichaelFaradayin
1824.
•VCRSwasfirstdevelopedbyJacob
Perkinsusinghandoperationin
1834.
•The first absorption
refrigerationmachine was
developed byaFrench
scientist,FerdinandCarre,in
1860.
•Thissystemmaybeusedin
boththedomesticandlarge
industrialrefrigeratingplants.
•Refrigerant,commonlyusedin
avapourabsorptionsystem,is
ammonia.
•TheVARSusesheatinsteadof
mechanicalenergyasinVCRS.
•Purelyaphysico-Chemical
processwhereasVCRSpure
mechanical.
•Inthevapourabsorptionsystem,the
compressorisreplacedbyanabsorber,a
pump,generatorandapressurereducing
valve.
•Thesecomponentsinvapourabsorption
systemperformthesamefunctionasthat
ofacompressorinvapourcompression
system.
•Inthissystem,thevapourrefrigerantfrom
theevaporatorisdrawnintoanabsorber
whereitisabsorbedbytheweaksolutionof
therefrigerantformingastrongsolution.
•Thisstrongsolutionispumpedtothe
generator-itisheatedbysomeexternal
source.
•Duringtheheatingprocess,thevapour
refrigerantisdrivenoffbythesolutionand
entersintothecondenserwhereitis
liquefied.
•Theliquidrefrigerantflowsintothe
evaporatorandthusthecycleiscompleted.

209. Low pressure ammonia vapour
leaving the evaporator enters
the absorber where it is
absorbed by the cold water in
the absorber.
The water has the ability to absorb
large quantities of ammonia vapour.
Theabsorptionofammonia
vapourinwaterlowersthe
pressureinthe-absorberwhich
inturndraws
moreammoniavapourfromthe
evaporatorandthusraisesthe
temperatureofsolution.
The strong solution from
absorber is pumped to the
generator by the pump by raising
pressure up to 10 bar.
The strong solution of ammonia
in the generator is separated by
some external source as gas or
steam.

210. This weak ammonia solution flows back to
the absorber at low pressure after passing
through the pressure reducing valve.
The high pressure ammonia vapour from
the generator is condensed in the
condenser to a high pressure liquid
ammonia.
During heating process, ammonia vapour
is driven off solution at high pressure and
leaving hot weak ammonia solution in
generator.
This liquid ammonia is passed to
expansion valve through the receiver and
then to the evaporator. This completes the
simple vapour absorption cycle

211. Coefficient of Performance of an Ideal Vapour Absorption Refrigeration System
Heat Supplied in Generator=Q
G),
Heat discharged from the condense=Q
C
Heat Rejected by absorber=Q
A
Heat absorbed by the refrigerant in the
evaporator =Q
E
Heat added bypump to refrigerant= Q
P
Neglecting the heat due to pump work
Q
P , we have according to First Law of
thermodynamics,
Qc = Q
G+ Q
E--------(1)
Let T
G= Temperature at which heat (Q
G)
is given to the generator,
Tc = Temperature at which heat (Qc) is
discharged to atmosphere from
condenser
T
E= Temperature at which heat (Q
E) is
absorbed in the evaporator.
Considered VARS as a perfectly
reversible system,
Initial entropy of the system=The
entropy of the system after the
change in its condition.
---------2
Considering 1 and 2
Solving 2 and 3
------3
Finally
Maximum coefficient of performance of
the system is given by

212. It may be noted that,
is the C.O.P. of a
Carnot refrigerator
working be
temperature limits of
T
Cand T
E
is the efficiency of a
Carnot engine
working between
temperature limits
of T
Gand Tc
The maximum C.O.P. may be written as
Representation of vapour absorption
refrigeration system

216. Practical Vapour Absorption system
Previouscyclediscussedisnot
veryeconomical.Inordertomake
thesystemmorepractical,itis
fittedwith
An analyser,
A rectifier and
Two heat exchangers.
These accessories help to
improve the performance.
Analyserisusedtoremovewater
vapoursformedingenerator.
Rectifier-Incasethewater
vapoursarenotcompletely
removedintheanalyser,adevice
calledrectifier(alsoknownas
dehydrator)isused.
Theheatexchangerisusedto
cooltheweakhotsolution
returningfromthegeneratorto
raisethetemperatureofthe
strongsolution.

217. Vapour Absorption
Refrigeration Systems Based
On Water-Lithium Bromide Pair

218. VARS based on H
2O –LiBr Pair
•Vapour absorption refrigeration systems using water-lithium bromide
pair are extensively used in large capacity air conditioning systems.
•In these systems water is used as refrigerant and a solution of lithium
bromide in water is used as absorbent.
•Since water is used as refrigerant, using these systems it is not
possible to provide refrigeration at sub-zero temperatures. Hence it is
used only in applications requiring refrigeration at temperatures above
0
o
C.
•Hence these systems are used for air conditioning applications. The
analysis of this system is relatively easy as the vapour generated in
the generator is almost pure refrigerant (water), unlike ammonia-water
systems where both ammonia and water vapour are generated in the
generator.

219. Lithium-Bromide System

220. VARS based on H
2O –LiBr Pair

222. COP of an Ideal VARS

223. Sample Problem in Simple VARS
9. The operating temperatures of a single stage vapour absorption
refrigeration system are: generator: 90
o
C; condenser and absorber:
40
o
C; evaporator: 0
o
C. The system has a refrigeration capacity of 100
kW and the heat input to the system is 160 kW. The solution pump
work is negligible.
•a) Find the COP of the system and the total heat rejection rate from
the system.
•b) An inventor claims that by improving the design of all the
components of the system he could reduce the heat input to the
system to 80 kW while keeping the refrigeration capacity and
operating temperatures same as before. Examine the validity of the
claim.

224. •Solution:
Sample Problem in Simple VARS

225. Solar VARS

226. Domestic Electrolux (Three fluid absorption system)
Three fluids are Ammonia (Refrigerant), Hydrogen (inert Gas) and Water (solvent)
Hydrogen (inert gas) used as to
increase the rate of evaporation.
Lighter the gas, faster the
evaporation.
Hydrogen is insoluble in water
and used in low pressure side.
Circulates from Absorber to
evaporator and back.
Strong solution of NH
3in water, is
heated in generator. NH
3vapours
separated from solution in water
separator, reaches to evaporator
via condenser. Weak solution
comes to absorber from water
separator. Ammonia evaporate in
evaporator in presence of H
2.
NH
3+H
2O comes to absorber, from where H
2gas returns to evaporator, NH
3
strong solution reaches to generator.

227. Electrolux (With Heat Exchanger)

229. Steam Jet Refrigeration

230. Thesteamjetrefrigerationsystemalso
knownasejectorrefrigerationsystem)
Oneoftheoldestmethodsof
producingrefrigerationeffect.
Thebasiccomponentsofthissystem
anevaporator,acompressiondevice
condenser,andarefrigerantcontrol
device.
Thissystememploysasteamejector
orbooster(insteadofmechanical
compressor) tocompress the
refrigeranttotherequiredcondenser
pressurelevel.
Inthissystemwaterisusedasthe
refrigerant.
Sincethefreezingpointofwateris0°C,
therefore,itcannotused for
applicationsbelow0
0
C.
Theboilingpointofaliquidchanges
withchangeinexternalpressure.In
normalconditionspressureexertedon
thesurfaceofanyliquidisthe
atmosphericpressure.
Ifthisatmosphericpressureisreduced
onthesurfaceofaliquid,bysome
means,thentheliquidwiIIstartboiling
atlowertemperature,becauseof
reducedpressure.
Thisbasicprincipleofboilingofliquid
atlowertemperaturebyreducingthe
pressureonitssurfaceisusedinsteam
jetrefrigerationsystem.
Theboilingpointofpurewater:
Atstandardatmosphericpressureof
760mmofHg(1.013bar)is100°C,
At0.014barwaterboilsat12°C,
At0.01barwaterboilsat7°C.
Thereducedpressureonthesurfaceof
waterismaintainedbythrottlingthe
steamthroughthejetsornozzles.
Principle of Steam Jet Refrigeration
System

231. Water as a Refrigerant
Waterisusedasarefrigerantinsteam
jetrefrigerationsystem,andthe
coolingeffectisproducedbythe
continuousvaporisationofapartof
waterinthe
evaporatoratreducedpressure.
WhenwateristobechiIIedfrom10°C
to5°C,atleastonepercentofwater
flowingthroughtheevaporatormust
bevaporised.
m =Mass of water in the evaporator in kg,
s=Specific heat of water = 4.2 kJ/kg
O
C,
hfg = Latent heat of vaporisation of water
at some reduced pressure in kJ/kg
qR=Heat removed from the water inkJlkg
Let one per cent of m kg of water is
evaporated by throttling the steam at
some reduced pressure (say at a
pressure of 0.085 bar
Thus, the total heat removed by this one
per cent of evaporated water
Fall in temperature of the remaining
water will be
Let
Itmeansthatifonekgofwateris
removedbyboilingonreducingsome
pressure,2400.5kJlkgofheatis
removedfromthewaterwhichis
requiredforitsevaporationandwater
becomescolderby5.77°C.Thisremoval
ofheatisacontinuousprocess.
(at pressure 0.085 bar, from steam
tables),

232. Working of Steam Jet Refrigeration System
The main components of system
are the flash chamber or
evaporator, steam nozzles, ejector
and condenser.
Thewarmwater
comingoutofthe
refrigeratedspace
issprayedintothe
flash water
chamber where
someofwhichis
converted into
vapours after
absorbing the
latent heat,
therebycooling
therestofwater.
The high pressure steam from the boiler is passed through
the steam nozzles thereby increasing its velocity.
This high velocity steam in the ejector would entrain the
water vapours from the flash chamber which would result
in further formation of vapours.
Themixtureofsteamandwatervapourpassesthroughtheventuri-tubeofthe
ejectorandgetscompressed.Thishightemperatureandpressurefedtothewater
cooledcondenserwhereitgetscondensed.Thecondensateisagainfedtothe
boilerasfeedwater.Constantwaterlevelinflashchamberismaintainedbymake
upwatersupply

233. Analysis of Steam Jet Refrigeration System
Point A represents initial condition of steam before passing through nozzle
Point B is the final condition of the steam, assuming isentropic expansion.
Point C is initial condition of the water vapour in evaporator. Point E is condition
of the mixture of high velocity steam from the nozzle and the entrained water
vapour before compression.
Assuming isentropic compression, the final condition of the mixture discharged
to the condenser is represented by point F.
Point D is condition of motive steam just before mixing with the water vapour.
Make-up water supplied at point G whose temperature is lower than condenser
temperature G
’
and is throttled to point H in the flash chamber.
Actual expansion
shown by AB
’
Actual
compress
ion
shown by
EF '

234. Efficiencies used in Steam Jet Refrigeration System
Nozzle efficiency.
The nozzle efficiency may vary from 85 to 90 per cent.
Entrainment efficiency.
The water vapours formed in the flash chamber or evaporator comes out with a
very low velocity as compared to the velocity of the steam (V) coming out of the
nozzle which is given by:
This kinetic energy enables the water vapours to come
out of the flash chamber or evaporator. The process is
called entrainment of vapour. During the entrainment of
water vapour, the entrainment reduced due to the
losses.This is taken into consideration by a factor
known as entrainment efficiency.
Compression efficiency.
/ Diffuser efficiency

235. Mass of Motive Steam Required
According to the law of conservation of
energy,
the available energy for compression =
the energy required for compression.
Let m
s= Mass of motive steam supplied
in kg/min,
m
V= Mass of water vapours formed from
the flash chamber /evaporator in
kg/min,
m = Mass of the mixture for
compression in kg/min = m
S+ m
V
We know that available energy for
compression= m
S(h
A-h
D)------(1)
Energy required for compression
= m (h
F
,
-h
E) = (m
S+ m
V) (h
F,-h
E)--(2)
Now according to law of conservation
of energy,
m
S(h
A-h
D) = (m
S+ m
V) (h
F’-h
E)--(3)
We know following efficiencies
Substituting the value of
from above equations in equation (3), we
have
Finally we have

236. Make-upwaterissuppliedatpointG
withenthalphyh
fg,throttledtopointH,
leavescorrespondingtothecondition
atpointC.Sincetheenthalpyofwatera
point G is equal to the enthalpy of water
at point H,
Therefore heat absorbed is
Since one kg of water vapour
requires m
Skg of motive steam,
therefore,
Mass of motive steam required per
Q tonne of refrigerating load
= Mass of water vapour per minute
x Motive steam required per kg of
vapour
The coefficient of performance of
the system is given by

237. Advantages:
a) It is flexible in operation; cooling capacity can be easily and quickly
changed.
b) It has no moving parts as such it is vibration free.
c) It can be installed out of doors.
d) The weight of the system per ton of refrigerating capacity is less.
e) The system is very reliable and maintenance cost is less.
f) The system is particularly adapted to the processing of cold water used
in rubber mills,, distilleries, paper mills, food processing plants, etc.
g) This system is particularly used in air-conditioning installations,
because of the complete safety of water as refrigerant and ability to adjust
quickly to load variations and no hazard from the leakage of the
refrigerant.
Disadvantages:
a) The use of direct evaporation to produce chilled water is usually limited
as tremendous volume of vapour is to be handled.
b) About twice as much heat must be removed in the condenser of steam
jet per ton of refrigeration compared with the vapour compression
system.
c) The system is useful for comfort air-conditioning, but it is not
practically feasible for water temperature below 4
o
C.

238. Cascade Refrigeration
The cryogenics means production of low temperature near to absolute zero e.g. 0
0
K
and used in the liquefactions of gases. The temperature from -100
O
C to 273
O
C (absolute
zero) are treated as low temperature.
The liquid oxygen boils at 90.2 K (-182.9
O
C), liquid hydrogen boils at 20.4K (252.6
O
C),
liquid helium boils at 1.1K (271.9
O
C)
The single stage VCRS are used upto -40
O
C

239. Two stage cascading

240. Two stage cascading PH & TS

241. Three stage cascading

242. Three stage cascading PH & TS