Aircraft Refrigeration Systems

1.Simple air cooling system

• Main compressor driven by a gas turbine,heat exchanger, cooling turbine and a cooling air fan
• The air required for refrigeration system is bled off from the main compressor.
• This high pressure and temperature air is cooled initially in heat exchanger where ram air is used for cooling.
•  It is further cooled in cooling turbine by the process of expansion.
• The work of this turbine is used to drive the cooling air fan which draws cooling air from the heat exchanger and exit to atmosphere.
• The air from the cooling turbine is sent to the cabin and cockpit where it gets heated by the heat of equipment and occupancy.

2. Bootstrap Air cooling system

• It has two heat exchangers instead of one and a cooling turbine drives a secondary compressor instead of cooling fan
•  The air bled from the main compressor is first cooled by the ram air in the first heat exchanger.
• The air is compressed to a higher pressure and temperature in the compressor of the cooling turbine.
•  A substantial amount of heat of compression is removed in the secondary heat exchanger and the air is cooled further as its expands through the turbine section of the cooling turbine.

3. Regenerative Air cooling system

• The high pressure and temperature air from the main compressor is first cooled by the ram air in the heat exchanger.
• This air is further cooled in regenerative heat exchanger.
• In a regenerative system, a part of the cold air from the cooling turbine is used for precooling the air entering the cooling turbine.
• Lower temperatures are obtained at the exit of the cooling turbine, however, this is at the expense of additional weight and design complexity.
• The cooling turbine drives a fan similar to the simple system.

4. The reduced ambient air-refrigeration system

• It includes two cooling turbines and one heat exchanger.
• The air reduced for the refrigeration system is bled off from the main compressor is cooled initially in the heat exchanger.
• The air required for cooling is taken from the first cooling turbine which lowers the temperature of rammed air which is quite high due to ramming action.
• The cooled air from the heat exchanger is passed through the second cooling turbine from where the air is supplied to the cabin.
• The work of cooling turbines is used to drive the exhaust fan (through reduction gears) which draws the cooling air from the heat exchanger.

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