1. air cycle cooling systems

2. Use of air cycle machines to adjust the temperature of the air directed into the passenger and crew compartment of this large aircraft. It is directed to the ability to provide cabin cooling air, it should be noted that the cabin could also be heated and pressurized. Large aircraft utilized air cycle cooling because of its simplicity, freedom from troubles and economy.

3. PRINCIPLE OF COOLING
When the gas (air) is compressed, it becomes cooled. If the pressure cylinder is connected to an air compressor and compressed air is forced into the cylinder, one can observe that the cylinder becomes warm or event hot, depending upon the level of compression and the rate at which the air is compressed. If the cylinder filled with highly compressed air is then allowed to cool to ambient temperature, the pressure in the cylinder will be reduced to a certain degree as the air is allowed to escaping will be much lower than the ambient temperature, due to the air expanding as its pressure returns to the ambient value.

4. This cool air can then be used as a cooling agent
This cool air can then be used as a cooling agent. In air cycle system, the air is continuously compressed and then the pressure is reduced by passing the air through the expansion turbine. The air is leaving expansion turbine is at low pressure and temperature. The cooled air is directed through ducting with control valves to regulate the amount of cooling air needed to produce the desired temperature.

6. SYSTEM OPERATION The system is composed of a Primary heat exchanger,
Primary heat exchange by pass valve,
Flow limiters,
Refrigeration unit,
Main shut off valve,
Secondary heat exchanger,
Refrigeration unit bypass valve,
Ram air shut-off valve and an air temperature control system.

7. SYSTEM OPERATION
Air from the cabin air conditioning and pressurization system is bled from the compressors of both engines. The engine bleed lines are cross connected and equipped with check valves to ensure a supply of air from either engine. A flow limiting nozzle is incorporated in each supply line ruptures and to prevent excessive hot air bleed through the rupture.