Correct Answer - Option 4 : Mass of refrigeration system is low
Explanation:
Aircraft cooling systems:
In an aircraft, cooling systems are required to keep the cabin temperatures at a comfortable level. Even though the outside temperatures are very low at high altitudes, still cooling of cabin is required due to:
- Large internal heat generation due to occupants, equipment etc.
- Heat generation due to skin friction caused by the fast moving aircraft.
- At high altitudes, the outside pressure will be sub-atmospheric. When air at this low pressure is compressed and supplied to the cabin at pressures close to atmospheric, the temperature increases significantly.
- Solar radiation
For low speed aircraft flying at low altitudes, cooling system may not be required, however, for high speed aircraft flying at high altitudes, a cooling system is a must.
Even though the COP of air cycle refrigeration is very low compared to vapour compression refrigeration systems, it is still found to be most suitable for aircraft refrigeration systems as:
- Air is cheap, safe, non-toxic and non-flammable. Leakage of air is not a problem.
- Cold air can directly be used for cooling thus eliminating the low temperature heat exchanger (open systems)
- The aircraft engine already consists of a high speed turbo-compressor, hence separate compressor for cooling system is not required. This reduces the weight per kW cooling considerably. Typically, less than 50% of an equivalent vapour compression system
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Design of the complete system is much simpler due to low pressures. Maintenance required is also less.
