Aircraft refrigeration system (air cooling system)

DEPARTMENT OF MECHANICAL ENGG. S.R.I.M.T, Lucknow
Ripuranjan Singh
Asst. professor
For any query contact at
ripuranjansingh999@gmail.com

Methods of Air Refrigeration Systems
• 1. Simple air cooling system,
• 2. Simple air evaporative cooling system,
• 3. Boot strap air cooling system,
• 4. Boot strap air evaporative cooling system,
• 5. Reduced ambient air cooling system, and
• 6. Regenerative air cooling system.

1.SIMPLE AIR COOLING SYSTEM
Fig:-Simple air cooling system

FIG:-T-S DIAGRAM FOR SIMPLE AIR CYCLE COOLING SYSTEM

IF V IS THE AIRCRAFT VELOCITY OR THE VELOCITY OF AIR RELATIVE TO THE AIRCRAFT IN METERS
PER SECOND, THEN KINETIC ENERGY OF OUTSIDE AIR RELATIVE TO AIRCRAFT,
From the energy equation, we know that
2000
v
hh
2
12 
2000
V
T.cT.c
2
1p2p 

p
2
12
c2000
V
TT 
1p
2
1
2
.c2000
1
T
V
T
T

1p
2
1
2
.c2000
1
'
T
V
T
T

and

• We know that C.O.P. of the air cycle
'T'T
'TT
)'T'(Tcm
)'T(Tcm
23
56
23pa
56pa







If Q tonnes of refrigeration is the cooling load in
the cabin, then the air required for the
refrigeration purpose,
Power required for the refrigeration system
kW
60
)''( 23 TTcm
p
pa 

and C.O.P. of the refrigerating system

2.Simple Air Evaporative Cooling system

T-s Diagram

3.BOOT-STRAP AIR COOLING SYSTEM
• he term Bootstrap as used in Air Cycle Refrigeration
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
The 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

4.Boot-strap Air Evaporative Cooling
System

T-s diagram

If Q tones of refrigeration is the cooling load in the cabin,
then the quantity of air required for the refrigeration purpose
will be

5.Regenerative air cooling system
Fig:-Regenerative air cooling system

Fig. :-T-s diagram for regenerative air cooling system

6. Reduced Ambient Air Cooling
System

Fig:-Reduced ambient air cooling system

Fig:-T-S diagram for reduced ambient air cycle cooling
system.For any query contact at

ADVANTAGES

Comparison of Various Air Cooling Systems
used for Aircraft
• Comparison of Various Air Cooling Systems used for
Aircraft are shown in Fig.
• These curves show the dry air rated turbine discharge
temperature (DART) against the Mach number.
• we see that the simple air cooling system gives maximum
cooling effect on the ground surface and decreases as the
speed of aircraft increases.
• .The boot strap system on the other hand, 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.
Fig. Performance curves for various air cooling systems.

Ques1.
An aircraft refrigeration plant has to handle a cabin
load of 30 tonnes. The atmospheric temperature is
17°C. The atmospheric air is compressed to a
pressure of 0.95 bar and temperature of 30° C due
to ram action. This air is then further compressed in
a compressor to 4.75 bar, cooled in a heat
exchanger to 67°C, expanded in a turbine to I bar
pressure and supplied to the cabin. The air leaves
the cabin at a temperature of 27°C. The isentropic
efficiencies of both compressor and turbine are 0.9.
Calculate the mass of air circulated per minute and
the C.O.P. For air, = 1.004 kJ/kg K and 1.4.

Q=30 TR ; T1=17° C=17+237=290 K ; p2=0.95 bar ; T2=30° C=30+273=303 K
; p3=p3'=4.75 bar ; T4=67° C=67+273=340 ;p5=p5'=1 bar ;
T6=27° C=27+273=300 K ; ; cp=1.004 kJ/kg K; cp/cv= =1.4
0.9
Let
Let
T2 = Temperature of air at the end of ramming or
entering the main compressor,
T3’ = Temperature of air leaving the main compressor
after isentropic compression,
T4 = Temperature of air leaving the heat exchanger, and
T5 ‘= Temperature of air leaving the cooling turbine

Ques.2
A boot-strap cooling system of 10 TR capacity is used in an
aeroplane. The ambient air temperature and pressure are 20°C
and 0.85 bar respectively. The pressure of air increases from
0.85 bar to 1 bar due to ramming action of air. "The pressure of
air discharged from the main compressor is 3 bar. The discharge
pressure of air from the auxiliary compressor is 4 bar. The
isentropic efficiency of each of the compressor is 80%, while
that of turbine is 85%. 50% of the enthalpy of air discharged
from the main compressor is removed in the first heat
exchanger and 30% of the enthalpy of air discharged from the
auxiliary compressor is removed in the second heat exchanger
using rammed air. Assuming ramming action to be isentropic,
the required cabin pressure of 0.9 bar and temperature of the
air leaving the cabin not more than 20° C, find : 1. the power
required to operate the system, and 2. the C.O.P. of the system.
Draw the schematic and temperature -entropy diagram of the
system. Take =1.4 and cp =1 kJ/kg K

solution
Given : Q = 10 TR ; T1 = 20° C = 20 + 273 = 293 K ; p1 = 0.85 bar ; p2 = 1 bar ;
P3=P3'=P4=3 bar ;p5 = p5' = p6 =4 bar ;  2C1C  80% =0.8 ; T =
85% = 0.85 ;  877 ' ppp 0.9 bar ; T8 =200
C= 20+273 =293 K ; y=
1.4; cp = 1 kJ/kgK

Thank You
For any query contact at ripuranjansingh999@gmail.com

Aircraft refrigeration system (air cooling system)

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