Refrigeration and Air Conditioning Engineering (Lecture 01)

Refrigeration and Air Conditioning Engineering (Lecture 01)

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FET 411, Refrigeration and Air
Conditioning Engineering
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Course outline
•Chapter 1: Introduction to Refrigeration
•Chapter 2: Refrigeration cycle
•Chapter 3: Equipments of Refrigerator
•Chapter 4: Properties of Refrigerant
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Reference books
•Refrigeration and Air Conditioning –P. L. Ballaney
•A text book of Refrigeration and Air Conditioning –R.S.
Khurmi
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Chapter 1: Introduction to Refrigeration
•Refrigeration may be defined as the process of removing heat
or heat energy from a body, that is below the temperature of
its surroundings.
Refrigeration
Natural
Mechanical
Compression
Absorption: Ammonia and
water vapor
Steam jet
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Objectives
•To understand why the storage life of foods and agricultural
products can be extended by refrigeration
•To learn the adverse effects of low temperature for certain
commodities
•To refresh our knowledge about thermodynamics, in particular the
first law of thermodynamics, the phase diagram and the Mollier
diagram
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Purpose of refrigeration of foods
-reduces postharvest losses
-preserves foods
-makes it possible to provide safe, wholesome food all consumers
have the right to expect
-by refrigerated transport, allows countries to export perishable
produce
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
How does it work?
Fig. Gas production rate as a function of developmental stage
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Q10 (reduction in reaction rate if temperature decreases by 10°C) typically
2.5 for biochemical reactions
• Respiration
• Texture change
• Microbial growth
Example
-Predictive microbiology: prediction of microbial growth/inactivation in
various conditions of temperature, gas concentration, salt etc.
-E.g. Pathogen Modeling Program
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Negative effects of refrigeration: Chilling injury
-Variety of symptoms: lesions, brown heart in pineaple, mealinessin
tomato, gerydiscoloration in banana
-Most tropical fruits are affected
-Typically below 12°C, depending on cultivar
-Believed to be caused by imbalance between saturated and unsaturated
lipids
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Importance of refrigeration
-Number of farmers has gradually increased: <5% of world population
-Cold chains are vital to ensure safety, quality and commercial value of perishable
foodstuffs
-75% of foods are processed, the majority involves one or more refrigeration steps
-Foods or ingredients are transported 2.5 times
-Approximately 70% of foods in developed countries are chilled or frozen when
produced, and 50% of all foods sold require refrigerated display at retailer level
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
A few numbers
-Annual purchase of chilled and quick-frozen foods is around 1200 billion
USD
-Refrigeration generates jobs: 1 out of 1000 jobs in industrialized
countries are in the equipment manufacturing field
-300000 jobs in the USA and 70000 in Europe in the installation and
sectors
-Annual investment in refrigerating equipment totals 170 billion USD
-More than 1 billion domestic refrigerators/freezers in the world
-300 m3 of cold storage worldwide
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Simple cooling systems
•Pot –in –Pot (M. Bah Abba)
-Two ceramic pots
-Smallest pot inside largest pot
-Wet soil in between
-Cooling via evaporation: latent heat (enthalpy removed from pot
-Rolex award
-Simple design, local manufacturing possible
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Thermodynamics of phase change
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Temperature Vs Total Heat
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
State diagram
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Units of Refrigeration
•Unit of refrigeration: Tonneof refrigeration (TR)
•A tonneof refrigeration is defined as the amount of refrigeration effect
produced by the uniform melting of one tonne(1000kg) of ice from and at
0 oCin 24 hrs.
•Latent heat of ice is 335 KJ/Kg, hence,
•1TR= 1000 Kg * 335 KJ/Kg in 24 hrs
= (1000*335)/ (24*60)
= 232.6 KJ/min (in actual 210 KJ/min or 3.5 KW)
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Coefficient of performance
•COP = Amount of heat extracted in the refrigerator (Q)/ amount of
work done (W)
= Q/W
•It is reciprocal of the efficiency of a heat engine
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Difference between Heat engine, Refrigerator and heat pump
COP (E) = Work done
(W)/ Heat supplied (Q2)
=(Q2 –Q1)/ Q2
COP (R) = Heat taken
(Q2)/ Work done (W)
=Q1/ (Q2-Q1)
COP (P) = Heat delivered
(Q1)/ Work done (W)
= Q1/ (Q2-Q1)
= COP (R) + 1
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Simple vapor compression refrigeration system
•It is named as vapor compression, due to low pressure vapor
refrigerant from the evaporator is changed to high pressure
vapor in the compressor.
•Refrigerant: NH3, CO2, SO2
•Advantage: small, less running cost, can be run over large
range of temperatures, COP is high.
•Disadvantage: Initial cost high, leakage problem
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Mechanism of a simple vapor compression refrigeration
system
1.Compressor:Low pressure, temp vapor refrigerant from evaporator drawn into
compressor at high temp through suction valve. The highly pressed and temp
vapor refrigerant is discharged into the condenser through discharge valve.
2.Condenser (cooler): Refrigerant cooled and condensed here. At this stage,
refrigerant gives up its latent heat to the surroundings condensing medium
(air/water).
3.Receiver: the condensed refrigerant stored here in a vessel.
4.Expansion valve (refrigerant control valve):allow the liquid high pressure
refrigerant in a controlled reducing rate. Some portion of refrigerant evaporates
here but greater are evaporate in evaporator.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
5. Evaporator: The liquid-vapor refrigerant are passed through evaporator
(consists of coils of pipe) at low pressure and temperature. Here, the
liquid refrigerant absorbs its latent heatofvaporisationfrom the medium
(air, water or brine) which is to be cooled.
High pressure side: discharge line, condenser, receiver and expansion valve.
Low pressure side: evaporator, piping from expansion valve to evaporator and
the suction line.
Check the link for more: https://www.mobileair.com/refrigeration-cycle
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Pressure-enthalpy diagram
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
•Red line: temperature
•Green line: constant volume curve
•Black line: quality curves or mass fraction of vapor
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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•COP = Refrigeration effect/ Work done
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Factors influencing COP
1.There is no pressure loss in condenser, evaporator, connecting pipes and
compressor valves.
2.There is no heat transfer form or to the system at any point except the
condenser and evaporator
3.Compression is isentropic.
4.Transmission efficiency is from motor to compressor is 100%
5.Condenser temperature increase then COP is decrease due to
decreasing refrigeration effect.
6.Subcooling
7.Superheating
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Actual refrigeration cycle
1.Theliquidrefrigerantinthecondensermaybeundercooled,
i.e.cooledbelowthecondensingtemperaturebefore
passingthroughtheexpansionvalve.Thiscanbeobtained
bylargequantitiesofcirculatingcoolingwaterwhichshould
beatatemperaturemuchlowerthanthecondensing
temperatures.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
2.Normallythegasleavestheevaporatorinsuperheatedcondition
beforeitentersthecompressor.Thissuperheatingmayoccurin
theevaporatorpipesleavingtheevaporatorbutstillinthecooled
space.Thustherefrigeratingeffectwillincreaseperkgof
refrigerantflow.Thissuperheatingmayoccurinthepipes
connectingtheevaporatordeliveryandthecompressorsuction,in
spiteofthesepipesbeinginsulated.Thusthisisalossoran
additionalloadonthecompressorandcondenserwithoutany
usefulcoolingeffectobtained.Thusthesepipesshouldbe
properlyinsulated.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

10. 3/30/2017
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3)Compressionhasbeenassumedisentropic,butinactualpracticeit
maybeverycomplex.Thecylinderwallmaybestabilizeata
temperaturebetweenthecoolsuctiongasandhotdischargegas.
Thusduringthefirstpartofcompressionheatmayflowfromthe
wallstothegasandinthelaterpartofthestrokethereversalinthe
directionofflowofheatmaytakeplace.
4)Therefrigeranthastoflowthroughpipesintheevaporator,
condenserandotherconnectingpipes.Inactualpracticedueto
frictionalresistancetoflow,thereispressurefallintheconnecting
pipes.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Effect of Subcooling
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Effect of Superheating
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
A-B:isentropiccompression
B-C:removal of superheat
C-D:removal of heat of condensation (isothermal)
D-E:expansion in expansion valve (isenthalpyl)
E-A:evaporation at the evaporator (isothermal)
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

11. 3/30/2017
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Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Pressure Enthalpy charts
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

12. 3/30/2017
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Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

13. 3/30/2017
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Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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•Cooling load
oRate of heat energy removal
o“Ton of refrigeration”: latent heat of fusion of 1 ton of ice per day = 3.52
kW
•Heat to be removed
oHeat of respiration
oLosses through ceiling, floor and wall
oHeat production of fans, lights, fork lifts, personnel
•Condenser
oHeat rejected to environment:
3 1( )
cq m H H 
1
2
3
H Enthalphy of refrigerant at exit from
the condonsor (kJ/kg)
H ethalphy of refrigerant at the beginning
of compression of stroke (kJ/kg refrigerant)
H ethalphy of refrigerant at the


 end
of compression of stroke (kJ/kg refrigerant)
m refrigerant mass flow rate (kg/s)Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Mathematical expressions: Design and
analysis
•Evaporator
•Compressor
•Coefficient of performance
oIndicator of efficiency of system
oRatio of useful effect to the work expended
oCoefficient Of Performance: heat absorbed by refrigerant / energy supplied
to compressor
oRefrigerant flow rate (q is heat to be removed)
2 1( )
eq m H H 
3 2
( )
w
q m H H 
2 1
3 2
H H
COP
H H



2 1
q
m
H H



c
e
w
q rate of heat exchanged in the condensor (kW)
q rate of heat exchanged from the evaporator (kW)
q rate of work done on the refrigerant (kW)



Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Charging of refrigeration system
•Aftercompletelyassembleofrefrigerationsystem,thewholesystemis
testedforleaks,driedandevacuation,itisreadyforcharging.
•Therefrigeranttobeusedisstoredinliquidforminsuitablecontainers.
•Theusualpracticeistofeedrefrigerantvaporfromthetopofthe
containerintothesuctionlineofthesystemwiththecompressorrunning
andcondenserinoperation.
•Therateofremovalofrefrigerantfromcontainer,isacceleratedby
immersinginhotwater.Itisimportanttosupplythecorrectamountof
refrigerantintothesystem.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Common troubles in refrigeration system
•Alargeportionofservicetroublewithrefrigerationsystemis
causedbyMOISTURE.
•Onesmalldropofliquidwatercanstopthecirculationof
refrigerantbyfreezingintheexpansiondevice.
•Othertroublessuchascorrosion,copperplatingand
chemicaldamagetoinsulationmayresultifmoistureis
presentinthesystem.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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How water may appear in refrigeration system
1.Incompletedryingoftheequipmentbeforecharging,
2.Lowsidesleaksadmittingairwhichcontainsmoisture,
3.Leakageinwater-cooledcondenser,
4.Waterformationthroughoxidationofcertainhydrocarbonsin
theoil
5.Waterdissolvedineitheroilorliquidrefrigerantwhenitis
placedinthesystemand
6.Decompositionofthemotorinsulationinhermeticallysealed
units.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Remedies of moisture removal
Byusingdessicant(dryingagent)orabsorbentand
chemicaldrierstoremovewaterfromthe
refrigerationsystem.
1.Absorbents:Granularaluminiumoxide(activated
alumina),silicondioxide(silicagel),
2.Chemicaldriers:anhydrouscalciumsulfate(drierite),
calciumoxideorquiklimeandcalciumchloride.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Troubles with non-condensable gases
•Theyarealsoservicetroubleswithrefrigeratingsystem.Theyincrease
operatingpressuresandtemperaturesanddecreaseefficiency.They
presentinrefrigerationsystemfromoneormoreofthefollowingsources:
1.Incompleteremovalofthegasusedforpressuretestingthesystemprior
tocharging,
2.Formationofnon-condensablegasbychemicalreactionswithinthe
system.
3.Airandothernon-condensablegasesdissolvedintherefrigerantwhen
chargedand
4.Leaksinthepiping.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Remedies for non-condensable gases
•Smallunit:itisremovedbywastingthecharge,evacuating
thesystemandrechargingwithfreshrefrigerant.
•Largeunit:itcanberemovedfromthetopofthe
condenserandfromthetopoftheevaporatorwithan
accompanyinglossofonlyasmallportionoftherefrigerant
charge.Theprocessofremovingnon-condensablegases
fromarefrigeratingsystemiscalledpurging.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST

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Tests for leakage of the refrigerant
1.Leakage of SO2: detected by the white smoke which
appears if a swab soaked with a 25% solution of aqueous
NH3 is brought near it.
2.Leakage of NH3: may be detected with burning sulfur
candle.
3.Leakage of freons(halogenated hydrocarbons): may be
detected by the use of haldetorch. (The halide torch
burns alcohol and the flame turns green in the presence
of freonvapours).
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Methods of defrosting
•In many compression refrigeration systems the evaporator is a direct expansion
coil used to cool and dehumidifying the air passes over it. If the condition of
operation require metal surface below 32 oF, frost will collect on the tubes and
fins and periodic defrosting is essential.
•The methods of collecting frosts are
i.Interrupted service
ii.Water spray
iii.Hot gas and hot oil
iv.Electric resistance heater adjacent coil or arrangement for heating coil
by passing low voltage current through the metal.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST
Control compression refrigeration system
•Small systems (household refrigerator and home AC): the compressor is
stopped when the cooling thermostat has been satisfied and it is started
again when further refrigeration is needed.
•Large systems: The centrifugal compressor’s capacity may be varied to
match a changing load by
i.Varying the speed
ii.Adjusting vanes all the inlet to the impellers
iii.Regulators which throttle the suction gas so as to keep the evaporator
pressure constant and control the volume
iv.Varying condenser pressure.
Md Rahmatuzzaman Rana
Assistant Professor, Dept of FET, SUST