Mumbai University > Mechanical Engineering > Sem8 > Refrigeration and Air Conditioning

Marks: 4M, 8M

Year: May2013, Dec2014

Boot strap type aircraft refrigeration system:

Fig. Boot Strap Aircraft Air Refrigeration System

• The ambient air undergoes ramming before the compressor. Assuming isentropic ramming (process 1-2 in figure).
• After compression (2-3), the air bled from the main compressor is cooled by ram air in the first heat exchanger or intercooler (3-4).
• This air is then compressed further in the secondary or auxiliary compressor (4-5) and is led to the second heat exchanger, again cooled by ram air (5-6).
• The air is then expanded in the cooling turbine (6-7) which drives the secondary compressor. This cooled air is then finally sent to the cabin.
• This system is preferred for high speed aircrafts and hence the pressure of air after ramming is comparatively high. So a cooling fan is not required since ram air will now automatically flow over the heat exchanger tubes.
• Multistage compression with intercooler decreases the compression work for this system and thus in turn improves the C.O.P.