Refrigeration

Refrigeration is a technique used for preserving food in low temperatures. This procedure slow down or stop most bacteria from dividing and thereby multiplying, but do not kill them.

1. Refrigeration
Amandeep Singh
Assistant Professor
Department of Biotechnology
GSSDGS KhalsaCollege, Patiala

2. Content
•Important terminologies in refrigeration
•Importance of refrigeration and factors for spoilage
•Factors affecting cold storage (controlled atmosphere)
•Principle of refrigeration and working of refrigeration system
•Applications of refrigeration in the preservation of various foods

3. Important terminologies in refrigeration
1) Refrigerant
•Working fluid in the refrigeration
•It is capable of absorbing heat at lower temperature and rejecting heat
at higher temperature in the form of sensible heat and latent heat.
Ice Water Vapour
Latent Heat of Melting
Latent Heat of Freezing
Latent Heat of Vaporization
Latent Heat of Condensation
Sensible Heat
Sensible Heat Sensible Heat

4. SensibleHeat(thatcanbesensed/felt)
•Itistheenergymovingfromonesystemto
anotherthatchangesthetemperaturewithout
changingitsphase.
•Whenthesubstanceisheated,andthe
temperaturerises,sotheheataddediscalled
sensibleheat.
•Thisincreaseinheatcanbefeltphysicallyor
measuredwithordinarythermometer.
LatentHeat
•Theheatneededtochangeoneformofmatter
toanotherwithoutchangeintemperature.
•Soitcanbelatentheatofvaporizationorlatent
heatofcondensation.

5. Characteristics of Refrigerant
•should be high
Latent heat of vaporization
•should be low
Condensing pressure
•should be low
Freezing temperature
•should be high
Critical temperature
•should be nontoxic, nonflammable, non-corrosive and
chemically stable
Toxicity, flammability, corrosion and
chemical stability
•should be low
Cost
•any leak of refrigerant to the environment should not cause
any harm
Environment friendly

6. Refrigerant examples
•Ammonia
•Chlorofluorocarbons (CFCs)
•Hydrochlorofluorocarbons(HCFCs)
•Hydrofluorocarbons (HFCs)
•Propane

7. 2) Cooling load
Coolingloadistherateofremovalofheatfromadefinedspaceinorder
tolowerthetemperatureofthatspacetoadesiredlevel.
Thecoolingloadsofrefrigerationsystemsaredesignatedwitha
commonunitcalledtonofrefrigeration(TR).

8. 3) Ton of refrigeration (TR)
Amountofheatrequiredtoberemovedfromonetonofwaterat0°Cin
ordertoconvertitintoiceat0°Cinoneday(24hours).
1TR= 12600 KJ/h or 210 KJ/min or 3.5 KW

9. 4)CoefficientofPerformance(COP)
Theefficiencyoftherefrigerationsystemisalsoindicatedas
CoefficientofPerformanceofthesystem.
Itistheratiooftheheatextractedintherefrigeratortotheworkdoneon
therefrigerant.
COP=Amountofheatextractedintherefrigerator(Q)
Amountofworkdone(W)
COP=Q
W

10. 5)RelativeHumidity
Itistheactualmassofwatervapourinagivenvolumeofmoistairto
themassofwatervapourinthesamevolumeofsaturatedairatthe
sametemperature.

11. Importance of refrigeration and factors for
spoilage
•Foodscanbecomespoiledduetochemicalreaction,physicalreactionoractionof
microbes.Microbesarepresentinair,water,soilandalsointhefoodweconsume.
•Loweringthetemperatureslowsdowntherapidrateofthesebacterialgrowthin
foods.Mostbacteriagrowatatemperatureof4°C(40°F)to60°C(140°F).
•Thisisthebasicprinciplebehindprolongingshelflifeofthefoodsweconsume
throughrefrigeratedstorage.

12. Importance of refrigeration
•Refrigeratedtemperaturesdonotslowthereactionratesasmuchas
freezingtemperaturessotheyarenotusedforlongtermstorage.
•Howeverrefrigeratedfoodsdonotsufferfromicecrystaldamageand
theydonothavetogothroughathawingtimebeforepreparationasdo
manyoftheirfrozencounterparts.
•Forthisreasonrefrigerationisastoragemethodofchoiceinmany
situations.

13. Microbial Growth
Microorganismsuchasbacteria,virus,yeast,moldpresentinair,water,
soilandlivingorganismsarecausesoffoodspoilage.Therearetow
typesofbacterialikepathogenicbacteriaandspoilagebacteria.These
bacteriahavesignificantroleinthespoilage,unacceptabletaste,
appearanceandaromaoffood.

14. Microbial Growth
•Pathogenicbacteriaaretherootcauseoffoodborneillness,cangrow
rapidlyinthetemperaturerangeof4°C(40°F)to60°C(140°F)
generallyreferredasdangerzone.
•Thepresenceofthesebacteriawillnothavetheimpactongeneral
appearance,tasteandodorofthefood.
•Whereasspoilagebacteriathatgrowatlowtemperaturesmayaffect
thecolour,smell,tasteandtextureofthefoods.Foranygood
refrigeration,thetemperatureshouldbelowerthan7.5°C.

15. Microbial Growth
Bacteriathatareabletogrowatrefrigeratedtemperaturesareclassified
aspsychotropic.Coldtemperaturesarenottheiroptimalrangeforrapid
growthbuttheirnumberscontinuetoincreaseat4°C.Most
psychotropicbacteriabelongtothegenusPseudomonasandtothe
lesserextentAchromobacter,Flavobacterium,Alcaligenes,and
Anthrobacter.

16. Factors affecting cold storage
(Controlled Atmosphere)
•Aspecialcommercialrefrigerationtechniqueiscontrolledatmosphereinwhich
theatmosphereoftherefrigeratedspaceisaltered.
•Theoxygencontentisremarkablyreducedandcarbon-dioxidecontentis
increasedandhumidityiscontrolled.
•Foodpreservationbyrefrigerationshouldstartverysoonafterharvestingand
mustbecontinuousuntilthefoodisconsumed.Handlingoflargevolumeoffood
requiresexpensiveandbulkyequipmentswhichisbothinconvenientand
uneconomical.
•Foodpreservationalsodependsonthefollowingfactorssuchasthetypeofthe
product,thelengthoftimetheproducthastobepreserved,thepurposeforwhich
productistobeused,theavailabilityoftransportationandstorageequipment.
•Thepreservationofperishablebyrefrigerationinvolvestheuseoflowtemperature
asameanofeliminatingorretardingtheactivityofspoilageagents.

17. Principle of Refrigeration
•Itisbasedontheprinciplethatabsorptionofheatbyafluid
(refrigerant)asitchangesfromaliquidtoagas,lowersthe
temperatureoftheobjectsaroundit.
•Themostcommontypeofrefrigerationsystemapplyingthisprinciple
isVapourCompressionRefrigeration(VCR)System.
•TheVCRSystemiswidelyusedinrefrigerationapplicationslike
refrigerator,watercooler,airconditionerandcoldstorage.
•Therefrigerationeffectisproducedattheevaporator.

18. Components of the VCR system
1.Compressor
2.Condenser
3.Expansion Valve/Throttling device
4.Evaporator

19. Low Pressure
Low Temperature
Vapour
High Pressure
High Temperature
Vapour
High Pressure
High Temperature
Liquid
Low Pressure
Low Temperature
Liquid
Low Pressure
Low Temperature
Vapour
Compressor Condenser Expansion Valve Evaporator

20. Working of refrigeration system
•Therefrigerantentersthecompressor(whichistheheartofrefrigeration
system)aslowpressureandlowtemperaturevapour.Hereitiscompressed
tohighpressureandhightemperaturesuperheatedrefrigerantvapor.
•Thecompressedrefrigerantentersintothecondenserwherethelatentheat
ofcondensationtakesplace.Hereitiscondensedtohighpressureandhigh
temperatureliquid.
•Thesuperheatedrefrigerantliquidenterstheexpansionvalvewhichlowers
thepressure.Thetemperatureoftheliquidalsocomesdownandconverted
tocoldliquid.
•Thiscoldrefrigerantnowentertheevaporator,whereitgetconvertedinto
vapourbyabsorbingtheheatfromthefooditemsandthusproducecooling
effect.Soproducedvapouragainenterthecompressorandtheprocessis
repeated.

21. Low Pressure
Low Temperature
Vapour
High Pressure
High Temperature
Vapour
High Pressure
High Temperature
Liquid
Low Pressure
Low Temperature
Liquid
Compressor
Condenser
Expansion
Valve
Evaporator
Refrigeration System
Heat