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Flight Controls and Environmental Control Systems
Published in Stephen J Wright, Aviation Safety and Security, 2021
The bleed air is too hot and too high pressure to directly duct into the aircraft cabin, as typically temperatures of the air are about 200°C. Hot bleed air from the engine compressors is metered through the bleed air valve, located in the engine pylon, on to the ECS pack: inside the pack unit. The air is further metered through a pack flow control valve (see Figure 4.5), passed through a primary heat exchanger (where there is a temperature reduction), then to the ‘air cycle machine bootstrap turbo machinery’ comprising of the compressor (C) and the turbine (T). The bootstrap compressor (C) centrifugally compresses the bleed air and thus raises the temperature and pressure, and the air is passed to a secondary heat exchanger, where there is a temperature reduction in the air. The air flows to a water extractor, which is required since ice crystals can form in the bootstrap which, if not removed, would cause significant damage to the turbine and associated turbo machinery. The air passes out of the turbine with an associated drop in temperature and pressure as the outlet bleed air expands rapidly. Finally, the cool, conditioned air is distributed into the cabin air system (Figure 4.5).
Cabin systems
Published in David Wyatt, Mike Tooley, Aircraft Electrical and Electronic Systems, 2018
Engine bleed air, with temperatures in the order of 150 and 200°C and a pressure of between 30-35 pounds per square inch (psi), is directed into a primary heat exchanger. External ram air (at ambient temperature and pressure) is the cooling medium for this air-toair heat exchanger. The cooled bleed air then enters the centrifugal compressor of the air cycle machine (ACM). This compression heats the air (the maximum air temperature at this point is about 250°C) and it is directed into the secondary heat exchanger, which again uses ram air as the coolant. Pre-cooling through the primary heat exchanger increases the efficiency of the ACM by reducing the temperature of the air entering the compressor; less work is required to compress a given air mass (the energy required to compress a gas by a given ratio increases with higher temperature of the incoming air).
One-dimensional and three-dimensional computational thermal fluid hybrid analysis-aided air distribution pipeline system design
Published in Engineering Applications of Computational Fluid Mechanics, 2020
Most commercial aircraft use an air-cycle machine (ACM) as a source of cool air. The cooled air from the ACM is mixed with the high-temperature bleed air from the engine to adjust its temperature. Considering the fuel efficiency, a certain percentage of cabin air will be recycled to maintain enough fresh air for the cabin passengers. These three sources of air are conveyed into the mix manifold and mixed thoroughly, then supplied to the different compartments of the aircraft, including the cockpit, forward cabin, afterward cabin, galley, lavatory and individual gaspers, as shown in Figure 1. Separate main pipes are used to extract air from the mix manifold for each compartment, and the conditioned air drawn from the mixer is distributed to various locations in the aircraft compartments through branch pipes. Each independent pipeline from the mix manifold can be considered as a subsystem.