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

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

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

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:

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 = hg@0.14MPa = 236.04 kJ/kg,

s1 = sg@0.14MPa = 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 = hf@0.8MPa = 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

&&

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.

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

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.

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

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

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

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.

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.

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.