The document summarizes the basic vapor compression refrigeration cycle. It consists of four main processes: (1) compression of refrigerant vapor in a compressor, (2) condensation of the high-pressure vapor into a liquid in a condenser, (3) expansion of the high-pressure liquid through a throttling valve or expansion device, and (4) evaporation of the low-pressure liquid in an evaporator. The refrigerant absorbs heat from the evaporator and releases heat in the condenser, allowing for transfer of heat from low to high temperature regions. The coefficient of performance (COP) measures the efficiency of the cycle. Proper selection of refrigerant depends on the application.

1. Basic Refrigeration Cycle
Made by
Engr. Zubair Latif
Comsats institute of information technology, Lahore

2. Introduction
A major application area of thermodynamics is refrigeration,
which is the transfer of heat from a lower temperature region to a
higher temperature one.
Devices that produce refrigeration are called refrigerators, and the
cycles on which they operate are called refrigeration cycles.
The most frequently used refrigeration cycle is the vapor
compression refrigeration cycle in which the refrigerant is
vaporized and condensed alternately and is compressed in the
vapor phase. Another well-known refrigeration cycle is the gas
refrigeration cycle in which the refrigerant remains in the gaseous
phase throughout

3. Principles of Refrigeration
 Liquids absorb heat when changed from liquid
to gas(latent heat of vaporization)
 Gases give off heat when changed from gas to
liquid.(latent heat of condensation)

4. Four basic processes
1. 1-2 isentropic compression (in a compressor)
2. 2-3 constant pressure heat rejection ( in a condenser )
3. 3-4 isentropic expansion ( in a metering device such as
throatling valve)
4. 4-1 constant pressure heat addition ( in a evaporator)

5. The cycle of cooling

6. Compressor
The refrigerant comes into the
compressor as a low-pressure gas, it is
compressed and then moves out of the
compressor as a high-pressure gas.

7. Condenser
The gas then flows to the condenser.
Here the gas condenses to a liquid, and
gives off its heat to the outside air.

8. Expansion Valve/
Metering Device
The liquid then moves to the expansion
valve under high pressure. This valve
restricts the flow of the fluid, and lowers
its pressure as it leaves the expansion
valve.

9. Evaporator
The low-pressure liquid then moves to
the evaporator, where heat from the
inside air is absorbed and changes it
from a liquid to a gas.

10. Compressor
As a hot low-pressure gas, the
refrigerant moves to the compressor
where the entire cycle is repeated.

12. Coefficient of performance
(COP)
• The performance of refrigerators and heat pumps is expressed
in terms of coefficient of Performance, defined as
COP = desired output / required input
Or
COP = Cooling effect/ work input
= QL/Wnet,input
• A rule of thumb is that the COP improves by 2 to 4 percent for
each °C the evaporating temperature is raised or the condensing
temperature is lowered.

13. Selecting the right refrigerant
• There are several types of refrigerants such as CFCS, ammonia,
hydrocarbons,( propane, ethane, ethylene etc.), Carbon dioxide,
air( in the air conditioning of aircraft) and even water ( in the
applications above the freezing point).
• The right choice of refrigerant depends on the situation at hand
• The industrial and heavy-commercial sectors were very satisfied
with ammonia, and still are, although ammonia is toxic but due
to its several advantages like higher COPs, low cost, no effect on
ozone etc.