BALOCHISTA

N UNIVERSITY

OF

ENGIN

EERIN

G & TE

CHNOLOGY

KHUZDAR

Refrigerants By Engr.Hashim Hasnain

REFRIGERANTS A refrigerant is a substance or a heat carrying medium which during a refrigerant cycle absorbs heat from a low temperature system and discades the heat absorbed to high temperature system,It’s a medium of heat transfer through a change in phase such as evaporation and condensation. Refrigerant is thus are the working substance in refrigeration system.“ Refrigerant acts as a transportation medium to move heat absorbed in the evaporator to the condenser where it is rejected ”.

CLASSIFICATION OF REFRIGERANTS

BASED ON WORKING PRINCIPLE

Based on Working Principle :-

REFRIGERANTS

PRIMARY REFRIGERANTS SECONDARY REFRIGERANTS

1) Used directly as working fluids.

2) Undergo phase change.

Eg, R134a, R404a

1) Liquids that are used to transport energy.

2) Not undergo any phase change.

Eg. Water , brines.

• Primary refrigerants: are those fluids, which are used directly as working fluids, for example in vapor compression and vapor absorption refrigeration systems

These fluids provide refrigeration by undergoing a phase change process in the evaporator. Secondary refrigerants: are those liquids, which are used for transporting thermal energy from one location to other. Secondary refrigerants are also known under the name brines or antifreezes

PROPERTIES OF IDEAL REFRIGERANT:1. The refrigerant should have low boiling point and low

freezing point.2. It must have low specific heat and high latent heat.

Because high specific heat decreases the refrigerating effect per kg of refrigerant and high latent heat at low temperature increases the refrigerating effect per kg of refrigerant.

3. The pressures required to be maintained in the evaporator and condenser should be low enough to reduce the material cost and must be positive to avoid leakage of air into the system.

4. It must have high critical pressure and temperature to avoid large power requirements.

5. It should have low specific volume to reduce the size of the compressor.

6. It must have high thermal conductivity to reduce the area of heat transfer in evaporator and condenser.

7. It should be non-flammable, non-explosive, non-toxic and non-corrosive.

8. It should not have any bad effects on the stored material or food, when any leak develops in the system.

9) It must have high miscibility with lubricating oil and it should not have reacting properly with lubricating oil in the temperature range of the system.10) It should give high COP in the working temperature range. This is necessary to reduce the running cost of the system. 11) It must be readily available and it must be cheap also.

TYPES OF PRIMARY REFRIGRANTS• 1) Halocarbon refrigerants• 2) hydrocarbon refrigerants• 3) azetropes• 4)Inorganic refrigerants

.

HALOCARBON REFRIGERANTS• These were the most commonly used refrigerants

until the ban on these compounds due to environmental reason. Essentially these refrigerants are compounds of chlorine,florine and carbon

LAMINAR AND TURBULENT BOUNDARY LAYER

REFRIGERANT

CHEMICAL NAME APPLICATION properties

R-11 Trichloromonofluoromethane

Centrifugal chillers/compressor

Non flammable,

R-12 Dichlorodifluoromethane Reciprocating & rotatory equipment

R-13 Monochlorotrifluoromethane

Low stage cascade system

R-13B1 Bromotrifluoromethane Low to medium temp. application

R-113 Trichlorotrifluoroethane Low capacity chillers

R-114 Dichlorotetrafluoroethane

High capacity chillers

R-500 Refrig. 152A/12

Reciprocating compressor

R-502 Refrig. 22/115

Reciprocating equipments

R-503 Refrig. 23/13 Commercial refrigeration

CFCs:

• Refrigerant R12: The refrigerant R12 is the most widely used refrigerant in the domestic and large commercial establishments. Its chemical formula is CCl2F2 and its boiling point is -300C at 1 bar. It is a non-flammable, non-explosive, non-irritating, non-toxic and odourless refrigerant. It 62 Refrigeration and Air Conditioning remains chemically stable up to 550 0C. Also, it does not affect the material of the refrigeration system. It is available in abundance and is quite cheap. However, its use is being discontinued nowadays for its contribution to ozone depletion which will be discussed later

• Refrigerant R13 :Its chemical formula is CClF3. it is a non-flammable, non-toxic and stable refrigerant. It is very suitable for achieving low temperatures in a cascade refrigeration system. Its specific volume is high and therefore, it is suitable for centrifugal compressors. However, it also has a negative effect on ozone depletion.

• Refrigerant R22: Its chemical formula is CHClF2. it is also a non-toxic, non-flammable, non-corrosive and non-irritating refrigerant. It is the most common refrigerant for use in large refrigeration systems and is preferred to

Refrigerant R114 Its chemical formula is C2Cl2F4. Its boiling point corresponding to 1 bar is about 30C. It has properties very similar to those of R12 with respect to water and oil combination. It is not suitable for low temperature refrigeration since it has negative evaporator pressure even at around 9 0C. It is non-toxic, non-explosive and non-corrosive even in the presence of water.

HYDROCARBON REFRIGERANTCombination of HYDROGEN+FLUORINE+CARBON.Excellent thermodynamic propertiesFlammableThis group consists of colorless fluids normally in gaseous

state and made up of various combinations of carbon and hydrogen

REFRIGERANT CHEMICAL NAMES APPLICATION

a. R-22 Monochlorodifluoromethane

Commercial A.C

a. R-123 Dichlorotrifluoroethane chillers

R-124 Chlorotetrafluoroethane Medium chillers

R-401A R-22 + R-152a + R-124 Medium temp. system

R-401B R-22 + R-152a + R-124 Transport refrigerator

R-402A R-22 + R-125 + R-290 Ice machine

R-402B R-22 + R-125 + R-290 Super market refrigeration

REFRIGERANT CHEMICAL NAMES APPLICATIONR-23 Trifluoromethane Low temp.

refrigerationR-134A Tetrafluoroethane Automative

system & commercial ref.

R-404A R-125 + R-143a + R-134a Medium & low temp.

R-407C R-32 + R-125 + R-134a R 22 replacement

R-410A R-32 + R-125 Residential A.CR-507 Refrig. 125/143a Commercial ref.

AZETOPESStable mixture of refrigerantsVapor and liquid phases retain identical composition over a

wide range of temperature

Refrigerant number

Mixing formula

application

R-500 73.8% R-12 and 36.2% R-152

Non flammable.

R-502 48% R-22.and 51% R-115

R-504 48% R-32 and 51% R-115

R-500. it is non flammable non toxic non corrosiveIt is used commercial industrial applications20% grater refrigerant capacity than R-12Boliling point -33R-502, low temperature -50Flammable non toxicBoling point is -46Low condencing temperature,increase the compressor life and

improves lubrication properties

R-504. non flammable non toxicBoiling point is -57It is used for low temperature application

INORGANIC REFRIGERANTS.These are non hydrocarbon refrigerants mostly naturally available

R-717 Ammonia

R-718 water

R-729 air

R-744 Carbon dioxide

R-764 sulphur dioxide

WATER AS REFRIGERANT

Water as refrigerant is used in absorption system .New developing technology has created space for it for use in compression cycles also.

But higher than normal working pressure in the system can be a factor in restricted use of water as refrigerant

Carbon DioxideNon Flammable, Non toxicInexpensive and widely availableIts high operating pressure provides potential for system size and

weight reducing potential.Drawbacks:Operating pressure (high side) : 80 barsLow efficiency

AMMONIA AS REFRIGERANT

Excellent thermodynamic characteristics: small molecular mass, large latent heat, large vapour density and excellent heat transfer characteristics

High critical temperature (132C) : highly efficient cycles at high condensing temperatures

Its smell causes leaks to be detected and fixed before reaching dangerous concentration

Relatively Low priceDraw back of Ammonia as Refrigerant

ToxicFlammable ( 16 – 28% concentration )Not compatible with copperTemperature on discharge side of compressor is higher compared to

other refrigerants

THERMODYNAMIC PROPERTIES• Boiling point :- It should have low boiling point.• Freezing point :- It should have low freezing point.• Evaporative pressure :- It should be above atmospheric pressure.• Condensing pressure :- It should have low condensing pressure.• Latent heat of vaporization :- It should have high latent heat of

vaporization.• Critical pressure and temperature :- It should be above the condensing

pressure and temperature. • Thermal conductivity :- It should have high thermal conductivity.• Co-efficient of performance :- COP has direct effect on running cost of

refrigeration cycle so higher the COP lower will be the running cost.

Thermodynamic PropertiesRefrigerants

R 12 R 22 R 134a

R 404a

R 407a

NH3 H2O CO2

B.P (⁰C) -28.8 -40.81

-26.2 -46.4 -45 -33 100 -57

F.P (⁰C)Latent heat of vaporization (KJ/kg)

166.95

233.75

215.9 143.68

235.57

1371.2

2.257

571.3

Critical temp. (⁰C)

112 96.15

100.95

72.07

82.2 132.4

374 30.98

Critical pressure (bar)

41.15

49.9 40.6 37.32

45.15

8.88 217.7

77.77

Specific heat at const. pressure (KJ/mol.K)

.074 .057 1.03 1.520

.0374

Refrigerants

R 12 R 22 R 134a

R 404a

R 407a

NH3 H2O CO2

B.P (⁰C) -28.8 -40.81

-26.2 -46.4 -45 -33 100 -78.3

F.P (⁰C) -157.7

-160 -96.66

------ ------- -77.7 0 -56.6

Latent heat of vaporization (KJ/kg)

166.95

233.75

215.9 143.68

235.57

1371.2

2.257

571.3

Critical temp. (⁰C)

112 96.15

100.95

72.07 82.2 132.4 374 30.98

Critical pressure (bar)

41.15

49.9 40.6 37.32 45.15 8.88 217.7

77.77

Specific heat (KJ/mol.K)

.074 .057 .08754

1.03 1.520 6.91 4.18 .0374

COP(@ 35’C) 3.677

3.701 3.586 3.603

CHEMICAL PROPERTIES• Toxicity :- It should be non toxic. It should not be harmful for

humans.• Corrosiveness :- It should not be corrosive and should not

have any effect on materials used in equipments.• Flammability :- It should be inert and should not catch fire

when subjected to high temperature.• Miscibility with oil :- It should not react with lubrication oil.• Chemical stability & inertness :- It should be chemically

stable for operating ranges of temperature.

PHYSICAL PROPERTIES• Specific volume :- It should be low in vapour state.• Viscosity :- It should have low viscosity.• Leakage Detection :- It should have less tendency to leak & if it leaking it

should have a pungent smell so that the leakage can be detected easily.