REFRIGERATION

REFRIGERATION
• Refrigeration defined as the providing, maintaining
temperature in the required region/space than its
surrounding temperature.
• In which device this process is under going is called
refrigeration machine.
• The Substance, which absorb heat from other
substance/space is called refrigerant. This is the working
fluid in the refrigeration system.
• It removes heat from low temperature region/space
(Evaporator) and transfer to high temperature
region/space (Condenser).
• Refrigerants are two types, one is Primary refrigerant,
and second is secondary refrigerant.
 Need for Refrigeration

• The growth of microorganisms is temperature dependent,

that growth declines as temperature falls, and that growth
becomes very slow at temperatures below +10 °C

• Use of refrigeration to conserve foodstuffs and natural ice

came into use for this purpose

Basic Concepts in Refrigration 3

 Application of Refrigeration
• Foodstuff production, processing, preservation
• Chemical processing industry
• Industrial and comfort air conditioning plants
• Drying plants, etc

Basic Concepts in Refrigration 4

 applications of refrigeration
 Domestic / Food Refrigeration: Food preservation, making
of ice cream , beverages , cool water ,dry products etc.

 Commercial Refrigeration / Comfort air-conditioning :

Conditioning / control of temperature , humidity , air
motion and purity of space. Air-conditioning of residential
buildings, offices , theaters , restaurants , shopping malls ,
seminar halls , hospitals

 Industrial Refrigeration : Ice plants , large food plants,

meat , poultry products, oil refineries , chemical plants,
machine tool industries, cotton mills , textile industries,
heat treatment of metals, printing works
 applications of refrigeration

 Medical Refrigeration: Preservation of drugs ,

bloods , eyes , preservation of surgical
equipments , human tissues etc

 Research Work Refrigeration : For research work

under low temperature applications, cryogenic
study, rocket fuels , synthetic rubber and oil
factory.

 Computer hardware / IT Refrigeration :

Maintaining low temperature in computer
environments.
 applications of refrigeration

.
 Basic Methods of refrigeration
Melting of a Solid (Non-Cyclic methods ):
Heat flows from space to Ice at 0°C and ice becomes
to water at 0°C ( 334.9 kJ/kg)
Sublimation of a Solid (Non-Cyclic methods ):
When solid carbon dioxide or Dry Ice exposed to
atmosphere , solid directly converts to vapor by
absorbing latent heat of sublimation ( 620 kJ /kg
at 1atm -78.5°C )
Evaporation of a liquid ( Cyclic-methods)
The cooling substance is not consumed and discarded
, but used again and again in a thermodynamic
cycle.
 Pure Substance & Refrigerants

1. A pure substance is one whose chemical composition

does not change during thermodynamic processes.
Refrigerants are examples of pure substances.
2. These days emphasis is on the use mixture of
refrigerants. The properties of mixtures also require
understanding of the properties of pure substances.
3. These substances also exist in three states. These also
undergo transformations usually from liquid to vapour
(evaporation) and vapour to liquid (condensation)
during heat absorption and rejection respectively
1. If a liquid (pure substance) is heated at constant pressure, the
temperature at which it boils is called saturation
temperature. This temperature will remain constant during
heating until all the liquid boils off.
2. At this temperature, the liquid and the associated vapour at
same temperature are in equilibrium and are called saturated
liquid and vapour respectively.
3. Similarly, if the vapour of a pure substance is cooled at
constant pressure, the temperature at which the
condensation starts, is called dew point temperature. For a
pure substance, dew point and boiling point are same at a
given pressure.
4. Similarly, when a solid is heated at constant, it melts at a
definite temperature called melting point. Similarly cooling of
a liquid causes freezing at the freezing point
1. For all pure substances there is a temperature at which all
the three phases exist in equilibrium. This is called triple
point.
2. At critical point there is no distinction between liquid state
and vapour state; these two merge together. At constant
pressure greater than critical pressure, P C when liquid is
heated in supercritical region, there is no distinction
between liquid and vapour.
• sub-cooled region
• wet region
• superheated region
Properties at Saturation
Therefore the properties of the liquid-vapour mixture can be
obtained by using the following equations
All properties with subscript ‘fg’ are the difference
between saturated vapour and saturated liquid states
Phase diagrams of Refrigerants
 unit of refrigeration

.
 unit of refrigeration

.
 Types of refrigeration
These are broadly classified into two categories:
I. Cyclic method of Refrigeration:
i. Mechanical-Compression Refrigeration System: The
most widely used refrigeration cycle method is
mechanical compression i.e., Vapour compression
refrigeration cycle
ii. Absorption Refrigeration: High load and Industrial
applications
iii. Evaporative Cooling: Air coolers works on this
principle
iv. Thermoelectric Refrigeration:
II. Non-Cyclic method of Refrigeration:
I. ICE Refrigeration
II. Dry ICE refrigeration
 types of refrigeration systems
1. Vapor Compression Refrigeration
2. Vapor Absorption Refrigeration
3. Air refrigeration
Notes for Vapor compression refrigeration:
(1) Vapor compression cycle are extensively used in refrigeration systems.
(2) Vapor compression cycle is used for most of small domestic and large
industrial applications
(3) Ideal compression vapor cycle is Reversed / Counterclockwise Rankine
cycle.
(4) Evaporation of a liquid is used to produce refrigeration and the process
of vaporization occurs when heat is absorbed from refrigerating space.
(5) Refrigerant used are ammonia , carbon dioxide , Freons etc. These days
eco-friendly tetra-fluoro-ethane (R134 α) is used as refrigerant in vapor
compression refrigeration.
 Principles of Refrigeration
REFRIGERATION SYSTEM COMPONENTS
The basic components of a refrigeration
system are:
- Evaporator
- Compressor
- Condenser
- Expansion Valve
- Refrigerant; to conduct the heat from the
product

Basic Concepts in Refrigration 21

 The Vapor-Compression Refrigeration Cycle
►The processes of this cycle are
Process 1-2: Two-phase
liquid-vapor mixture of
refrigerant is evaporated
through heat transfer from the
refrigerated space.
Process 2-3: Vapor refrigerant
is compressed to a relatively
high temperature and
pressure requiring work input.
Process 3-4: Vapor refrigerant
condenses to liquid through
heat transfer to the cooler
surroundings.
Process 4-1: Liquid refrigerant
expands to the evaporator
pressure.
Working principle of Standard vapor compression Refrigeration
System based on Ideal vapor compression refrigeration cycle
1-2 Constant pressure heat absorption in an Evaporator:
1. The refrigerant enters the evaporator at state 1 as a low quality
saturated mixture, and it completely evaporates by absorbing
heat from the refrigerated space.
2. The refrigerant leaves the evaporator as saturated vapor and
reenters the compressor, completing the cycle
2-3 Isentropic compression in a Compression:
3. In an ideal Vapour Compression Refrigeration (VCR) cycle, the
refrigerant enters the compressor at state 2 as saturated vapour
and is compressed isentropically to the condenser inlet pressure
as state 3.
4. The temperature of the refrigerant increase during this isentropic
compression process to well above the temperature of the
surrounding medium.
3-4 Constant pressure heat rejection in a Condenser:
1. The refrigerant then enters the condenser as superheated vapor at
state 3 and leaves as saturated liquid at state 4 as a result of heat
rejection to the surroundings.
2. The temperature of the refrigerant at this state is still above the
temperature of the surroundings.

4 -1 Throttling in an Expansion device:

3. The saturated liquid refrigerant at state 4 is throttled to the
evaporator pressure by passing it through an expansion valve or
capillary tube.
4. In this process the temperature of the refrigerant drops below the
state 1 i.e., temperature of the refrigerated space.
Working principle of Standard vapor compression Refrigeration
System based on Ideal vapor compression refrigeration cycle
DRY compression versus WET compression
ACTUAL vapor compression refrigeration cycle
ACTUAL vapor compression refrigeration cycle
ACTUAL vapor compression refrigeration cycle
 Evaporator
1. The purpose of the evaporator is to remove unwanted
heat from the product
2. Refrigerant contained within the evaporator is boiling at a
low-pressure. The level of this pressure is determined by
two factors:
i. The rate at which the heat is absorbed from the product
to the liquid refrigerant in the evaporator.
ii. The rate at which the low-pressure vapor is removed
from the evaporator by the compressor
3. When leaving the evaporator coil the liquid refrigerant is
in vapor form.
4. Types of Evaporators
i. Flooded evaporators
 Compressor
1. The purpose of the compressor is to draw the low-temperature,
low-pressure vapor from the evaporator via the suction line.
2. When vapor is compressed it rises in temperature.
3. The compressor transforms the vapor from a low-temperature
vapor to a high-temperature vapor, in turn increasing the
pressure.
4. These are three types
1. Hermetic:
i. It is one in which both motor and compressor are kept in a single outer
welded steel shell. It is leak proof but cannot be repaired.
ii. This usually last for 2-3 years but works silently.
2. Semi hermetic:
i. These are also sealed with the motor in the same housing but the casing is
darted type and can be repaired effortlessly.
ii. These are usually last 3-10 years
3. Open
i. It is one in which both motor and compressor are kept with out casing (no shell).
It can easily repaired.
ii. It is general type of compressor
 Condenser
1. The purpose of the condenser is to extract heat from the refrigerant
to the outside air.
2. Fans mounted above the condenser unit are used to draw air
through the condenser coils.
3. The temperature of the high-pressure vapor determines the
temperature at which the condensation begins.
4. As heat has to flow from the condenser to the air, the condensation
temperature must be higher than that of the air.
5. The high-pressure vapor within the condenser is then cooled to the
point where it becomes a liquid refrigerant once more, whilst
retaining some heat.
6. There are three types of condensers:
i. Air cooled are generally used un domestic refrigerators
ii.Water cooled are generally used in heavy load applications (plants,
Central AC)
iii.Evaporative are a combination of water cooled and air cooled
condensers. In these condensers the hot refrigerant flows through the
coils. Water is sprayed over these coils.
 Expansion Devices
1. The expansion valve is located at the end of the liquid line,
before the evaporator. The high-pressure liquid reaches the
expansion valve, having come from the condenser.
2. The valve then reduces the pressure of the refrigerant as it
passes through the orifice, which is located inside the valve.
3. On reducing the pressure, the temperature of the refrigerant
also decreases to a level below the surrounding air.
4. This low-pressure, low-temperature liquid is then pumped in to
the evaporator.
5. These are basically 2 types
1. Constant restriction types
1. Capillary tube
2. Variable restriction type
1. Automatic expansion valve
2. Thermostatic expansion valve
3. Float valves
 Automatic expansion valve

Thermostatic expansion valve

Capillary tube
 Reversed Carnot cycle
1. Reversing the Carnot cycle does reverse the directions of heat and
work interactions.

2. A refrigerator or heat pump that operates on the reversed Carnot cycle

is called a Carnot refrigerator or a Carnot heat pump.

3. The reversed Carnot cycle is the most efficient refrigeration cycle

operating between two specified temperature levels.

4. It sets the highest theoretical COP.

 Reversed Carnot cycle
VS
vapor compression refrigeration cycle
 refrigerants
It is defined as any substance that absorbs the heat through
vaporization or expansion and loses it through condensation in a
Refrigerating system .
It is the working fluid in Refrigerating system
(1) Inorganic Refrigerants : Ammonia, Carbon dioxide , sulphur dioxide
dioxide, water and Air.
(2) Organic Refrigerants : Various Hydro carbons and Halo Carbons.
The Halo Carbon refrigerants were first developed by an American
Company “R.I DuPont de Numours & Co.” under market trade
mark as F-11, F-12 and F-22, called Freon groups. Further to keep
order so many new refrigerants having complicated names, the “R”
numbering system was established in 1957 by Du Pont and persists
today as Industry standard.
Designation / Numbering System of Inorganic Refrigerants:
R-(700 + Approximate Molecular Weight )
Ammonia : R-(700 + 17) = R-717
 The desirable properties of a refrigerants are:
1. High critical temperature to have large isothermal energy transfer.
2. The specific heat of liquid should be as small as possible and of vapour
should be as high as possible to give less superheating of vapour.
3. High latent heat of vaporization to get more refrigeration effect.
4. Large conductivity to reduce size of condenser and evaporator.
5. Low specific volume of vapour
6. Low freezing point such that there is no blockage during flow through
evaporator.
7. Non corrosive to metal and inert so as to not react with other materials
and commodities of the refrigeration system.
8. Non-toxic
9. Low boiling point
10.Non-flammable and non-explosive
11.Low cost and easily available
12.Easy to liquefy at moderate pressure and temperature
13.Easy of locating leaks by odour or suitable indicator
14.Mixes well with oil.
15.Low viscosity so that pressure drop is small.
 Identification Refrigerant by Number

Refrigerant No Name and chemical formula

R-11 Trichloromonofluoromethane (CCl3F)

R-12 Dichlorodifluoromethane (CCl2F2)

R-22 Monochlorodifluoromethane (CHClF2)

R-500 Mixture of 73.8% R-12 and 26.2% R-152a

R-502 Mixture of 48.8% R-22 and 51.2% R-115

R-717 Ammonia (NH3)

R-134a Tetrafluoroethane (CH2FCF3)

Formula generation C m H n F p Cl q

Designated by R-(m-1)(n+1)(P)
 refrigerants
ASHRAE: American Society of Heating, Refrigerating and Air Conditioning Engineers
Designation / Numbering System of Organic Refrigerants:

Digit Numbers of entities Result

1st Number of Carbon-Carbon bonds 0

2nd Number of Carbon atoms - 1 (2-1) = 1

3rd Number of Hydrogen atoms + 1 (1+1) =2

4th Number of Fluorine atoms 3

R-123

Note : The number is omitted if the number is zero.

Halo CARBON refrigerants
selection of refrigerants
selection of refrigerants
 desirable properties of an ideal refrigerants
(1) Thermodynamics Properties
1. Positive evaporating pressure and moderately low positive
condensing pressure to avoid leakage of atmospheric air into the
system and to use light weight equipment and piping on the
higher pressure side of the system.
2. Higher critical Temperature : Greater than condensing
temperature for ease of condensation .
3. Low boiling / evaporating temperature : Low temperature at
atmospheric conditions to avoid vacuum in the system.
4. Low freezing /solidification temperature : Lower than boiling /
evaporating temperature to avoid solidification and choking of
flow. Most refrigerants have freezing point below – 30 ° C.
5. High latent heat of vaporization : Increase the refrigerating
capacity per kg of refrigerant.
 desirable properties of an ideal refrigerants
(2) Chemical Properties
1. Non-toxicity : Vapors should not be harmful to human and
product stored.
2. Non-irritability : There should be zero or very low irritability and
anesthetic effect of the vapors .
3. Non-flammable and non-explosive : It should not catch fire with
little leakage.
4. Inertness and chemical stability : It should not react with metals
and do not form harmful products in the presence of oil and
water. During entire cycle it should remain stable and not
change its chemical composition.
5. Non-corrosive
6. Oil solubility : It should carry oil to condenser and evaporator as
it reduces the heat transfer coefficient.
 desirable properties of an ideal refrigerants
(3) Physical Properties
1. Low specific volume of vapor : Reduces the equipment size.
2. High heat transfer characteristics (a) High thermal conductivity
(b) High heat transfer coefficients (c) low specific heat in liquid
form ( d ) low viscosity
3. Low specific heat in liquid form and high specific heat in the
vapor form : Increase the refrigerating capacity per kg of
refrigerant.
4. High electrical insulation strength : When comes in contact with
motor winding i.e. in hermitically sealed compressors.
(4) Other Properties
1. Easy leakage detection : Pleasant distinct odor so as to know
about its leakage. 2. Availability and Cheep cost
3. Easy handling. 4. Low power consumption / ton of
refrigeration
 properties and uses of some refrigerants
(1) Ammonia
Condensing Pressure 12 bar
Evaporating Temperature 0 °C for 1 bar
Critical Properties 132.6 °C , 116 bar
Freezing temperature - 77.8 °C
Latent heat of vaporization 1312.6 kJ / kg

1. Large latent heat : Hence small Refrigerating equipment.

2. Moderate working pressures : Hence large ice plant and cold
storage plants.
3. Excellent heat transfer characteristics
4. High dissolving capability of moisture and hence no ice formation
5. Attacks nonferrous metals
6. Non-corrosive to ferrous metals : Hence steel pipes are used
7. Insoluble in mineral oils 8. Toxic 9. Strong intolerable smell and
hence easily detectable.
 properties and uses of some refrigerants
(2) Carbon Dioxide
Condensing Pressure 70 bar
Evaporating Temperature - 78.5 °C for 1.01325 bar
Critical Properties 34 °C
Freezing temperature -110 °C
Latent heat of sublimation 62 kJ / kg

1. Low specific volume : Hence compact Refrigerating

plant.
2. Non-corrosive and non-flammable
3. High concentration leads to suffocation
4. Cheap
5. High condensing pressure : Demits to heavier working
parts , greater consumption / ton of refrigeration and
low COP.
 properties and uses of some refrigerants
(3) Sulphur Dioxide
Condensing Pressure 45 bar

1. Advantageous low pressure : Hence used

in small plants
2. Highly toxic
3. Non-flammable
4. Highly corrosive and attacks ferrous
metals.