3. Refrigeration is a process of removal of heat from a
substance at a temperature lower than the
surrounding with the aid of external work.
In a refrigeration system, the rate at which the heat is
absorbed in a cycle from the interior space to be
cooled is called Refrigerating Effect.
Refrigeration
4. *
*In a refrigerator, a medium called Refrigerant
continuously extracts the heat from the
refrigerator which is to be kept cool at
temperatures less than the atmosphere &
finally rejects to it.
*Refrigerant acts as a heat exchange medium.
*e.g.- Ammonia, Freon, Methyl Chloride, Carbon
dioxide, Isobutane.
5. Unit of Refrigeration & Ice making
Capacity
The capacity of a refrigeration system is expressed in
tons of refrigeration which is the unit of refrigeration.
A ton of refrigeration is the quantity of heat absorbed
in order to form one ton of ice in 24 hours when the
initial temperature of water is 0°c.
1 Ton of Refrigeration = 210 kJ/min = 3.5kW
Ice making capacity is the capacity of the refrigerating
system to make ice beginning from water to solid.
S.I. unit of ice making capacity is kg/hr.
6. Coefficient of
Performance
The coefficient of performance(briefly written as C.O.P.)
is the ratio of desired effect to the work input.
Mathematically,
(C.O.P.)refrigerator = Desired effect = Q2____
Work Input Q1-Q2
7. T1=Tsurr
Source T1
T2<Tsurr
Sink T2
R Work Input,W=Q1-Q2
Heat Absorbed, Q2
Heat Rejected, Q1
Refrigerator is a
reversed heat engine.
It extracts Q2 amount of
heat from sink & releases
Q1 amount of heat to
source.
Input—Work(Q1-Q2)
Output– Heat
Refrigerator
10. 11
Type of Refrigeration
Vapour Compression Refrigeration
Refrigeration cycle
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
11. 12
Type of Refrigeration
Vapour Compression Refrigeration
Refrigeration cycle
Low pressure liquid refrigerant in
evaporator absorbs heat and
changes to a gas
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
12. 13
Type of Refrigeration
Vapour Compression Refrigeration
Refrigeration cycle
The superheated vapour enters the
compressor where its pressure is
raised
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
13. 14
Type of Refrigeration
Vapour Compression Refrigeration
Refrigeration cycle
The high pressure superheated gas
is cooled in several stages in the
condenser
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
14. 15
Type of Refrigeration
Vapour Compression Refrigeration
Refrigeration cycle
Liquid passes through expansion device,
which reduces its pressure and controls the
flow into the evaporator
Condenser
Evaporator
High
Pressure
Side
Low
Pressure
Side
Compressor
Expansion
Device
1 2
3
4
15. Advantages
Very mature technology.
It has very less running cost.
It has smaller size for the given capacity of refrigeration.
It can be employed over a large range of temperatures.
The C.O.P. is very high.
Disadvantages
Many systems still use HCFC refrigerants, which contribute
to depletion of ozone layer.
Initial cost is high.
The prevention of leakage of refrigerant is the major
problem in vapour compression refrigeration.
16