The present invention relates to a mixing device suitable for use in an aircraft air-conditioning system, and to a method of operating such a mixing device.
In a modern aircraft the passenger cabin, or sections of the passenger cabin, the freight compartment, or sections of the freight compartment, and the cockpit constitute different climate zones, which are conventionally air-conditioned, both in flight and on the ground, by means of an air-conditioning system specific to aircraft. Furthermore, the aircraft air-conditioning system is utilized to dissipate heat from heat-generating components on board the aircraft, e.g., electrical or electronic components. In the air-conditioning units of the aircraft air-conditioning system, the hot compressed air drawn in from the aircraft's engine compressors or auxiliary engine compressors is expanded and cooled to a desired low temperature.
The air processed in the air-conditioning units is fed as cooled fresh air to a mixing device, where it is mixed with recirculation air sucked out of an air-conditioned area of the aircraft, e.g., the passenger cabin. The mixed air produced in the mixing device, made up of cold fresh air processed by the air-conditioning units and recirculation air sucked out of an air-conditioned area of the aircraft, is ultimately utilized to air-condition the different climate zones of the aircraft. If the climate zones of the aircraft have to be cooled, the cold fresh air produced by the air-conditioning units is fed to the mixing device, often at a temperature of <0° C. Consequently, because of the moisture contained in the fresh air and/or recirculation air, ice or snow can accumulate in the mixing device or the ducts connected to the mixing device.
It is known from DE 10 2006 037 539 A1 that fresh air lines through which cold fresh air flows from the air-conditioning units of an aircraft air-conditioning system are protected from icing by the introduction of warm drawn-in engine air, controlled by trim valves.
DE 10 2009 003 937 A1, on the other hand, teaches that, to reduce the risk of icing in ducts through which cold fresh air flows in an aircraft air-conditioning system, the geometry of the ducts shall be designed in such a way as to avoid the creation of areas in which a fresh air stream passed through the ducts has a reduced flow velocity, especially in ducts with a small cross-section of flow.
Finally, DE 10 2010 014 354 A1 describes a mixing device suitable for use in an aircraft air-conditioning system, where premixing cold air fed to the mixing device in a first premixing chamber, and premixing warm air fed to the mixing device in a second premixing chamber, can improve the mixing quality and thereby minimize the accumulation of ice or snow in the mixing device, or the ducts connected to the mixing device, due to inadequate mixing of the air streams fed to the mixing device.