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1Content: Content: The ideal vaporThe ideal vapor--compression
refrigeration cyclecompression refrigeration cycle ActualActual
VaporVapor--CompressionCompression RefrigerationRefrigeration
CycleCycle Heat Pump System for Heating and CoolingHeat Pump System
for Heating and Cooling Innovative Innovative
VaporVapor--CompressionCompression RefrigerationRefrigeration
CycleCycle GasGas RefrigerationRefrigeration CyclesCycles
AbsorptionAbsorption RefrigerationRefrigeration SystemsSystems
RefrigerantsRefrigerants SelectionSelection
Refrigeration CyclesRefrigeration Cycles
Refrigeration affects many areas of Refrigeration affects many
areas of your lifeyour life
The obvious:The obvious: Refrigerator/Freezers allow food
preservationRefrigerator/Freezers allow food preservation Air
conditioningAir conditioning
Refrigerated fishing boats allow preservation of Refrigerated
fishing boats allow preservation of catchcatch
Refrigerated trucks are used to ship fruits/meatsRefrigerated
trucks are used to ship fruits/meats Refrigeration makes possible
medical procedures Refrigeration makes possible medical
procedures
that call for lowering body temperaturesthat call for lowering
body temperatures
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2Refrigerator and Heat PumpRefrigerator and Heat PumpThe
objective of a refrigerator is to remove heat (QL) from the cold
medium; the objective of a heat pump is to supply heat (QH) to a
warm medium.
Schematic diagram of the ideal vaporSchematic diagram of the
ideal vapor--compression refrigeration cyclecompression
refrigeration cycle
Condenser
Evaporator
Compressor
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3Simple view of household refrigeratorSimple view of household
refrigerator
TT--s Diagram of the Ideal Refrigeration Cycles Diagram of the
Ideal Refrigeration Cycle
Process 11--22 Isentropic Compression ProcessIsentropic
Compression ProcessProcess 22--33 P = constP = const. Heat
Rejection Process. Heat Rejection ProcessProcess 33--44
ExpansionExpansion underunder Throttling Process, Throttling
Process, h = consth = constProcess 44--11 P = constP = const. Heat
Addition Process. Heat Addition Process
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4PP--h Diagram of the Ideal Refrigeration Cycleh Diagram of the
Ideal Refrigeration Cycle
Process 11--22 Isentropic Compression ProcessIsentropic
Compression ProcessProcess 22--33 P = constP = const. Heat
Rejection Process. Heat Rejection ProcessProcess 33--44
ExpansionExpansion underunder Throttling Process, Throttling
Process, h = consth = constProcess 44--11 P = constP = const. Heat
Addition Process. Heat Addition Process
Coefficient of Performance in Refrigeration Coefficient of
Performance in Refrigeration CyclesCycles
inputWorkeffectCooling
inputRequiredoutputDesiredCOPR ==
12
41RCOP hh
hhw
qnet,in
L
==
inputWorkeffectHeating
inputRequiredoutputDesiredCOPHP ==
12
32
innet,
HHPCOP hh
hhw
q==
For Heat Pumps:For Heat Pumps:
For Refrigerators and Air Conditioners:For Refrigerators and Air
Conditioners:
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5Example 10-1 A refrigerator uses refrigerant-134a as the
working fluid and operates on an ideal vapor-compression
refrigeration cycle between 0.14 and 0.8 MPa. The mass flow rate of
the refrigerant is 0.05 kg/sec. Show thecycle on a T-s diagram with
respect to saturation lines. Determine (a) the rate of heat removal
from the refrigerated space and the power input to the compressor,
(b) the rate of heat rejection to the environment and (c) the
coefficient of performance.
kW 93.8Q
)42.9305.272(05.0Q , 0 wand SSSF law1st 3,-2Condenser
:rejectheat of rate The (b)
H
H23
====
=
&&& HH qmhhq
Property of R-134a : Table A-11 A-13State 1 Sat. vapor @ P1 =
0.14 MPa h1 = [email protected] = 236.04 kJ/kg,
s1 = [email protected] = 0.9322 kJ/kg-KState 2 Superheated@ P2 = 0.8
MPa and s2 = s1 = 0.9322 kJ/kg-K, h2 = 272.05 kJ/kg State 3
Sat.liquid @ P3 = P2= 0.8 MPa, h3 = [email protected] = 93.42 kJ/kg State 4
Throttling, h4 = h3 = 93.42 kJ/kg
kW13.7Q
)42.9304.236(05.0Q , 0 wand SSSF lawst 1 1,-4 Evaporator
:inputpower and space edrefrigerat from removeHeat (a)
L
L41
====
=
&&& LL qmh h q
kW 80.1W
)04.23605.272(05.0W , 0qand SSSF law1st 2,-1Compressor
in
in21
====
=
&&& inin wmh h w
96.380.113.7
WQ COP
:eperformanc oft coefficien The (c)
in
L ===kWkW
&&
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6ActualActual VaporVapor--ccompressionompression
RefrigerationRefrigerationCycleCycle
Example 10-2 Refrigerant-134a enter the compressor of a
refrigerator as superheated vapor at 0.14 MPa and -10oC at rate of
0.05 kg/sec and leave at 0.8 MPa and 50oC. The refrigerant is
cooled in the condenser to 26oC and 0.72MPa and is throttled to
0.15MPa. Determine (a) the rate of heat removal from the
refrigerated space and the power input to the compressor, (b) the
isentropic efficiency of the compressor and (c) the coefficient of
performance.
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712
12c
:compressor of efficiency isentropic The (b)
hhhh s
Property of R-134a : Table A-11 A-13State 1 Superheated@P1 =
0.14 MPa and T1=-10oC h1 = 243.40 kJ/kg, State 2 Superheated@ P2 =
0.8 MPa and T2=50oC h2 = 284.39 kJ/kg State 3 Sat.liquid @ = 0.72
MPa and T3=26oC h3 = hf@26C = 85.75 kJ/kg State 4 Throttling, h4 =
h3 = 85.75 kJ/kg
kW88.7Q
)75.8540.243(05.0Q , 0 wand SSSF lawst 1 1,-4 Evaporator
:inputpower and space edrefrigerat from removeHeat (a)
L
L41
====
=
&&& LL qmh h q
kW 05.2W
)40.24339.284(05.0W , 0qand SSSF law1st 2,-1Compressor
in
in21
====
=
&&& inin wmh h w 84.305.2
88.7WQ COP
:eperformanc oft coefficien The (c)
in
L ===kWkW
&&
State 2s Superheated@ P2 = 0.8 MPa and s2s=s1=0.9606kJ/kgK h2s =
281.05 kJ/kg
91.9%
919.040.24339.28440.24305.281
c
==
Heat Pump System for Heating and CoolingHeat Pump System for
Heating and Cooling
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8CascadeCascade RefrigerationRefrigeration SystemsSystems
Two cycles connected
through HX.
Application: Moderately low temperature (TL) Large pressure
range in cycle
Improve COP of the system
MMultistageultistage CompressionCompression
RefrigerationRefrigerationSystemsSystems
Application: Moderately low temperature (TL) Large pressure
range in cycle
Better heat transfer than HX.
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9MultipurposeMultipurpose RefrigerationRefrigeration
SystemsSystems withwitha a SingleSingle CompressorCompressor
Application: Refrigeration at more than one temperature
LiquefactionLiquefaction ofof GasesGases
Application: Operate at cryogenic temperatures(below -100oC)
Desire product
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10
GasGas RefrigerationRefrigeration CyclesCycles
Application: Simple and lighter components Refrigerate in the
aircraft Process 11--22 Isentropic Compression ProcessIsentropic
Compression Process
Process 22--33 P = constP = const. Heat Rejection Process. Heat
Rejection ProcessProcess 33--44 Isentropic ExpansionIsentropic
Expansion, , s = consts = constProcess 44--11 P = constP = const.
Heat Addition Process. Heat Addition Process
AnAn OpenOpen--CCycleycle AircraftAircraft CoolingCooling
SystemSystem
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11
AbsorptionAbsorption RefrigerationRefrigeration
SystemsSystems
Heat-driven system
A refrigerant is a fluid used for heat transfer in a A
refrigerant is a fluid used for heat transfer in a refrigeration
system. Most refrigerants absorb heat during refrigeration system.
Most refrigerants absorb heat during evaporation at low temperature
and low pressure and reject evaporation at low temperature and low
pressure and reject heat during condensation at a higher
temperature and heat during condensation at a higher temperature
and higher pressure. higher pressure.
Refrigerants most commonly used refrigeration systems can
Refrigerants most commonly used refrigeration systems can be
classified into four groups:be classified into four groups:
Classification of RefrigerantsClassification of Refrigerants
halocarbons,halocarbons,azeotropesazeotropes,,hydrocarbons,
andhydrocarbons, andinorganic compoundsinorganic compounds
Definitions of RefrigerantsDefinitions of Refrigerants
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12
HydrocarbonsHydrocarbons
Refrigerants belonging to the hydrocarbon group are ethane,
Refrigerants belonging to the hydrocarbon group are ethane,
propane, butane and propane, butane and isobutaneisobutane..
They are produced from petroleum in an oil refinery. They are
produced from petroleum in an oil refinery.
This group of refrigerants is used in the refrigeration systems
This group of refrigerants is used in the refrigeration systems in
oil in oil refineries and the petrochemical industry due to their
low costrefineries and the petrochemical industry due to their low
cost and and ready ready availablilityavailablility. .
Hydrocarbons are flammable and so safety precautions are of
Hydrocarbons are flammable and so safety precautions are of utmost
importance in the petrochemical industry.utmost importance in the
petrochemical industry.
Inorganic compoundsInorganic compounds
Inorganic compounds were refrigerants used in refrigerant this
gInorganic compounds were refrigerants used in refrigerant this
group roup are ammonia NHare ammonia NH33
HalocarbonsHalocarbons
Refrigerants belonging to the halocarbon group are derivatives
Refrigerants belonging to the halocarbon group are derivatives of
the hydrocarbons obtained by substituting chlorine or fluorinof the
hydrocarbons obtained by substituting chlorine or fluorine e for
the hydrogen atoms in methane and ethane. for the hydrogen atoms in
methane and ethane.
As chlorine and fluorine are both halogens, this group of As
chlorine and fluorine are both halogens, this group of refrigerants
is called the halogenated hydrocarbons or refrigerants is called
the halogenated hydrocarbons or halocarbons.halocarbons.
They are sometimes referred to They are sometimes referred to
freonsfreons which are colourless, which are colourless,
nonnon--inflammable, noninflammable, non--corrodentcorrodent to
most metals and generally to most metals and generally
nonnon--toxic toxic
Common refrigerants in this group are RCommon refrigerants in
this group are R--11, R11, R--12, R12, R--13 and 13 and
RR--22.22.
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13
AzeotropesAzeotropes
An An azeotropeazeotrope is a mixture of two substances which
cannot be is a mixture of two substances which cannot be separated
into its components by distillation. separated into its components
by distillation.
It evaporates and condenses as a single substance and Its It
evaporates and condenses as a single substance and Its properties
are completely different from its constituents. properties are
completely different from its constituents.
For example, For example, azeotropeazeotrope RR--500 is a
mixture composed of 73.8 500 is a mixture composed of 73.8 per cent
Rper cent R--12 and 26.2 per cent R12 and 26.2 per cent
R--152.152.
Terminology of RefrigerantsTerminology of Refrigerants
In the early days of refrigeration, refrigerants were called by
In the early days of refrigeration, refrigerants were called by
their their chemical names. chemical names.
However, a numbering system has been developed.However, a
numbering system has been developed.
Each kind of refrigerant is represented by a number, and in
fronEach kind of refrigerant is represented by a number, and in
front t of this number is a prefix `Rof this number is a prefix `R
which represent 'Refrigerant'. which represent 'Refrigerant'.
Before 'R' is used as the prefix, 'Freon' & 'Before 'R' is
used as the prefix, 'Freon' & 'GenetronGenetron', the trade ',
the trade names of refrigerants produced by two companies.names of
refrigerants produced by two companies.
For example, the RFor example, the R--12 they produced is called
Freon12 they produced is called Freon--12 and 12 and
GenetronGenetron--12.12.
The digits related to number of fluorine, hydrogen and carbon
The digits related to number of fluorine, hydrogen and carbon atoms
in the molecule.atoms in the molecule.
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14
Selection of a suitable refrigerantSelection of a suitable
refrigerant
It depends on many factors, such as the evaporating temperature
It depends on many factors, such as the evaporating temperature
required during operation, the coefficient of performance COP,
srequired during operation, the coefficient of performance COP,
safety afety requirements, and the size and location of the
refrigeration plarequirements, and the size and location of the
refrigeration plant. nt.
In order to select a suitable refrigerant for a refrigeration
syIn order to select a suitable refrigerant for a refrigeration
system of stem of known size and evaporating temperature, the
following factors muknown size and evaporating temperature, the
following factors must be st be considered:considered:
The volume flow rate required per kW of refrigeration
capacityThe volume flow rate required per kW of refrigeration
capacity The coefficient of performance COPThe coefficient of
performance COP Safety requirementsSafety requirements Physical
propertiesPhysical properties Operating propertiesOperating
properties Cost.Cost.