The document details various aircraft refrigeration systems, highlighting the need for cooling due to both external and internal heat sources. It describes several types of air refrigeration cycles, including simple, bootstrap, regenerative, and reduced ambient systems, and compares their advantages and disadvantages. Key features and operational principles of these systems are discussed, focusing on their cooling efficiencies and application in different aircraft environments.

1. AIRCRAFT REFRIGERATION
SYSTEM

2. Why there is a need of cooling an aircraft?
• External Heat sources
– Solar radiations directly coming from the sun
– Skin friction causing rise in temperature of air.
• Internal Heat sources
– Human beings
– Electrical and Electronics components
– Engine parts

3. Types of Air Refrigeration Cycle
• Air cycle refrigeration is one of the earliest
methods used for cooling.
• The key features of this method is that, the
refrigerant air remain gaseous state
throughout the refrigeration cycle.
• Based on the operation, the air refrigeration
system can be classified into
– Open Cycle
– Closed Cycle

4. Open Cycle

5. Closed Cycle

6. Open Cycle Vs Closed Cycle
Open Cycle Closed Cycle
Air is directly led to the space to be
cooled.
Dense air passed through pipes all the
time.
Since air is supplied to the refrigerator at
atmospheric pressure, the volume of air
handled by the compressor is large.
Suction pressure is higher than
atmospheric pressure so a smaller volume
of air is to be handled by the compressor.
Moisture leads to the formation of frost at
the end of expansion thus drier is used.
Pressure ratio can be reduced which
results in higher COP.

7. Advantages of Air Refrigeration System
• Air is used as refrigerant, which is easily
available and inexpensive.
• Refrigerant (Air) is non-toxic, non-flammable,
non-corrosive.
• Weight per tonne of refrigeration is quite low
(compared to other systems).
• The cold air can be directly used for
refrigeration so there is no need for separate
evaporator.

8. Disadvantages of Air Refrigeration System
• Lower C.O.P. compared to other refrigeration
cycle.
• Running cost is high.
• The mass of air required to circulate in the
system is very high when compared to other
type of refrigeration cycle due to low specific
heat capacity.

9. Types of Aircraft Refrigeration System
1. Simple air refrigeration system
(a) Without evaporative cooling
(b) With evaporative cooling
2. Boot strap air refrigeration system
(a) Without evaporative cooling
(b) With evaporative cooling
3. Regenerative air refrigeration system
4. Reduced ambient air refrigeration system

10. Simple Air Refrigeration System
(Without Evaporative Cooling)
T-S Diagram

11. Stagnation Temperature of air

12. Flow rate of air and Power required

13. COP of the system

14. Simple Air Refrigeration System
(With Evaporative Cooling)
T-S Diagram

15. Calculations of Power Required
and COP of the system

16. Bootstrap Air Refrigeration System
• Features of the system
1. Bootstrap indicates a system
in which the pressure of the
working fluid is raised in two
levels by using two
compressors before the
working fluid which is air,
expands in the turbine
section
2. Main components of this
system are:
- Two heat exchangers (air
cooler and after-cooler)
- A secondary compressor,
which is driven by the turbine
of the cooling system

17. Bootstrap Air Refrigeration System
(Without Evaporative Cooling)

18. Bootstrap Air Refrigeration System
(Without Evaporative Cooling)

19. Bootstrap Air Refrigeration System
(With Evaporative Cooling)
T-S Diagram

20. Air Flow Rate and Power Required
• If Q tonnes of refrigeration is the cooling load
in the cabin, then the quantity of air required
for the refrigeration purpose will be

21. Regenerative Air Refrigeration System
Features of the system:
1. Two heat exchangers but
does not requires ram air
for cooling the air in the
second heat exchanger.
2. Air from the primary heat
exchanger is further
cooled with the portion of
refrigerated air bled after
expansion in the turbine.
3. Lower turbine discharge
temperature but at the
expense of further
complications and
additional weight.

22. Regenerative Air Refrigeration System
T-S Diagram

23. Reduced Ambient
Air Refrigeration System
• Features of the system
• In the reduced ambient
system, there are two
expansion turbines, one in the
cabin air stream and another
in the cooling air stream.
• Both the turbines are
connected to the shaft driving
the fan which absorbs all the
power.
• The turbine for the ram air
operates from the pressure
ratio made available by the
ram air pressure.

24. Reduced Ambient
Air Refrigeration System

25. Dry Air Rated Temperature (DART)
• It is the temperature in terms of which the
comparison of different types of aircraft is
made.
• It is the temperature of the discharged air
from the expander if there is no condensed
moisture is present.
• Rating of aircraft: kg of air per unit time at
the design DART.

26. Comparison of Different
Aircraft Refrigeration Systems
• Simple Air Cooling System
gives maximum cooling effect
on the ground surface and
decreases as the speed of
aircraft increases.
• Boot Strap System requires
the air plane to be in flight so
that the ram air can be used
for cooling in the heat
exchangers.
• For high speed aircrafts, the
boot strap evaporative or
regenerative systems are used
because they give lower
turbine discharge temperature
than the simple cooling system