Subject:- Refrigeration and Air Conditioning

Topic:- Introduction to Refrigeration

Difficulty:- Low

Air Conditioning in aircraft is more difficult compared with the vehicles moving on the ground because of extreme cold conditions at high altitudes and rapid changes of surrounding atmosphere. The introduction of high speed jet transport air-planes in passenger services has greatly increased the important of aircraft air-conditioning in recent years. The temperature and pressurization must be capable of responding to rapid changes of ambient temperature and pressure as airplane climbs and descends.

Advantages: • Air Distribution: the source for cabin pressurization and ventilation is air compressor as air can be bled from the compressor because all modern power systems are axial air compressor coupled with gas turbine. This provide a definite source of fresh air and at a pressure adequate to maintain required cabin pressure over a wide range of operating conditions.

• High pressure bleed air has a certain disadvantages for pressuring, over a wider range of operating conditions. High pressure exercised to assure that air is free from engine oil contamination.

• A portion of the cabin air may be recirculated but it should be filtered and purified. The recommended ventilation rate is 6 m3 min per passenger for cock pit crew members.

• Refrigeration systems used for Aeroplane Air-conditioning: an air-cycle or vapour cycle refrigeration system can be used for aeroplane air-conditioning. The main advantage of air-cycle refrigeration system is its light weight, while the main disadvantages are low C.O.P. and poorer ground cooling.

• Vapour Cycle Refrigeration System: The vapour cycle systems has higher COP than air cycle but it is generally heavier. It has an additional advantage of providing ground cooling with an electrical power source and this is most important consideration in adopting for aeropane cooling.

• Modern Aeroplane using vapour cycle system are equipped with alternators providing 400 pcs power which permits relatively high rotational speeds and results in considerable lighter equipment. Vapour compressor driven by air-turbiines are also developed which operate at 80000 rpm and above. The shaft seal and speed control are the main problems with compressors.