Compressors in Refrigeration

Compressors are the most vital part of any refrigeration system. So study of these becomes very important in view of their areas of applications

1. Unit: 5 Compressors and their
typestypes
Prepared by:
Ankur Sachdeva (ME)
Assistant Professor
KIET Group of Institutions
Ankur Sachdeva, Assistant Professor (ME)

2. Recapitulation of VCRS
•Compressor:Itisamachineusedto
compresstherefrigerantfromthe
evaporatorandtoraiseitspressure
sothatthecorresponding
temperatureishigherthanthatof
thecoolingmedium.
•Condenser:Itisanimportantdevice
usedinthehighpressuresideofa
refrigerationsystem.Itsfunctionisto
usedinthehighpressuresideofa
refrigerationsystem.Itsfunctionisto
removeheatofthehotvapour
refrigerantdischargedfromthe
compressor.
•ThrottlingDevice:Itdividesthehigh
pressuresideandthelowpressure
sideofarefrigerationsystem.
•Evaporator:Itsfunctionistoabsorb
heatfromthesurroundinglocation
ormediumwhichistobecooled,by
meansofarefrigerant.
Ankur Sachdeva, Assistant Professor (ME)

3. Devices and Controls used in
Refrigeration
Ankur Sachdeva, Assistant Professor (ME)

4. COMPRESSORSCOMPRESSORS
Ankur Sachdeva, Assistant Professor (ME)

5. Compressors
•Itisthemostimportantpartofanyvapour
compressionrefrigerationsystemandusuallymost
costliest.
•Itremoveslowtemperatureandlowpressure
refrigerantvapoursfromthecoolingcoilthroughthe
suctionline.suctionline.
•Itcompressestheserefrigerantvapoursbyincreasing
thepressureandtemperatureresultinginanincrease
ofboilingpointoftherefrigerant,
•Itdischargestherefrigerantvapoursofhigh
temperatureandpressuretocondenserthrough
dischargeline.
Ankur Sachdeva, Assistant Professor (ME)

6. Classification of Compressors
1. Based on Working Principle
Ankur Sachdeva, Assistant Professor (ME)

7. Classification of Compressors
2. Based on arrangement of compressor
motor or external devices
-Open Type
-Hermetic (or Sealed Type)-Hermetic (or Sealed Type)
-Semi-Hermetic (Or Semi-Sealed Type)
Ankur Sachdeva, Assistant Professor (ME)

8. Reciprocating Compressor
•Areciprocatingcompressoris
alsocalledapistoncompressor
whichadoptsthebackandforth
pistonmotioninacylinder
synchronizedwithsuctionand
dischargevalvestocompressthe
vaporizedrefrigerantfromalow
pressureandtemperaturetoa
highpressureandtemperature.highpressureandtemperature.
•Themotionofthepistonis
achievedviaacrankshaftwhich
convertsmotorrotationsto
pistonreciprocations.
•Eachoperationcycleincludes
threeactions:suction,
compressionanddischarge.Each
crankshaftrotationcanachieve
thesethreeactionsinsequence;
asaresult,thegasdisplacement
isdiscontinuouswhichcauses
vibration.
Ankur Sachdeva, Assistant Professor (ME)

9. Rotary Vane Compressor
•Arotary-vanecompressorisalso
knownasarotarypistoncompressor
becausethefunctionofthevaneis
similartothatofapiston.
•Thefixedcasingisknownasa
cylinder.Thevanesplitsthespace
betweenthecylinderandtherolling
pistonintotwosections(suctionand
discharge).discharge).
•Astherollingpistonrotates,these
twovolumesareincreasedand
decreasedtoachievegassuction,
compressionanddischarge.
•Thiscompressortypecanalsobe
sub-classifiedbythedrivespeed
(constantandvariable)andnumber
ofvanes.
•Eachoperationcycleincludesfive
actions:start,suction,compression,
dischargeandend.
Ankur Sachdeva, Assistant Professor (ME)

10. Working of a Rotary Vane
Compressor
Ankur Sachdeva, Assistant Professor (ME)

11. Screw Compressor
•Screwcompressorsuseapair
ofhelicalrotorsorscrews
whichmeshtogetherto
compresstherefrigerant
betweenthem.
•Theycanproducehigh
pressureforasmallquantity
ofgasandconsumelessofgasandconsumeless
powerthanreciprocating
compressors.
•Theyhavelowtomedium
initialandmaintenancecosts
andfewmovingparts.
•However,theyhavedifficulty
indirtyenvironments,high
rotationalspeeds,andshorter
lifeexpectanciesthanother
designs.
Ankur Sachdeva, Assistant Professor (ME)

12. Working of Screw Compressors
Ankur Sachdeva, Assistant Professor (ME)

13. Scroll Compressor
•Scrollcompressorsusetwooffset
spiraldisksnestedtogetherto
compresstherefrigerant.Theupper
diskisstationarywhilethelowerdisk
movesinorbitalfashion.
•Scrollcompressorsarequiet,
smooth-operatingunitswithfew
movingpartsandthehighest
efficiencyratioofallcompressor
movingpartsandthehighest
efficiencyratioofallcompressor
types.
•Arotary-scrollcompressorisusedto
compresslargervolumesofgaseous
refrigeranttoahigherpressureand
temperatureviaafixedandorbital
scroll.
•Scrollcompressorsarecommonly
usedinautomobileairconditioning
systemsandcommercialchillers.
Ankur Sachdeva, Assistant Professor (ME)

14. Working of Scroll Compressors
Ankur Sachdeva, Assistant Professor (ME)

15. Centrifugal Compressor
•Centrifugalcompressorsusethe
rotatingactionofanimpellerwheel
toexertcentrifugalforceon
refrigerantinsidearoundchamber
(volute).
•Unlikeotherdesigns,centrifugal
compressorsdonotoperateonthe
positivedisplacementprinciple,but
havefixedvolumechambers.
•Theyarewellsuitedtocompressing•Theyarewellsuitedtocompressing
largevolumesofrefrigerantto
relativelylowpressures.The
compressiveforcegeneratedbyan
impellerwheelissmall,sosystems
thatusecentrifugalcompressors
usuallyemploytwoormore
stages(impellerswheels)inseriesto
generatehighcompressiveforces.
•Centrifugalcompressorsaredesirable
fortheirsimpledesign,fewmoving
parts,andenergyefficiencywhen
operatingmultiplestages.
Ankur Sachdeva, Assistant Professor (ME)

16. Working of
Centrifugal Compressor
Ankur Sachdeva, Assistant Professor (ME)

17. Open Type Compressor
•Inthistype,compressorand
motorworksastwo
separateunitsandthey
haveadistinctcasingfor
bothofthem.
•Thecompressoris
connectedtothemotorbyconnectedtothemotorby
abeltorcrankshaft.
•Opentypecompressorsare
notleakproofastheyare
mostsusceptibletothe
leaks.
•Theyrelyonshaftsealsin
ordertopreventleakageof
workingfluidsandthento
retaintheinternalpressure.
Ankur Sachdeva, Assistant Professor (ME)

18. Hermetic (Sealed Type)
Compressor
•Inhermeticcompressors,
themotorandthe
compressorareenclosedin
thesamehousingto
preventrefrigerantleakage.
•Thehousinghaswelded•Thehousinghaswelded
connectionsforrefrigerant
inletandoutletandfor
powerinputsocket.
•Asaresultofthis,thereis
virtuallynopossibilityof
refrigerantleakagefromthe
compressor.
Ankur Sachdeva, Assistant Professor (ME)

19. Semi-Hermetic
( or Semi-Sealed Type) Compressor
•Semi-hermeticcompressor
alsoenclosesthemotor
compressorbycommon
housing.
•Itpreventstheleakageof
thefluid.
•Itpreventstheleakageof
thefluid.
•Inasemi-hermetic
compressor,thecasingis
boltedtogetherinsteadof
rigidlywelding.
•Thecasingcanbeopened
torepairmotorandother
components
Ankur Sachdeva, Assistant Professor (ME)

20. Characteristics of Compressors
Ankur Sachdeva, Assistant Professor (ME)

21. Applications of Compressors
Ankur Sachdeva, Assistant Professor (ME)