modern jetliner: heating system - how it workselectric or other?air is very cold at high altitudes
Actually, the problem is to get rid of heat, not to add it. Cabin pressure is picked off of the engine compressor stages; the compression of the outside air heats it, and it has to be cooled by a heat exchanger before being vented to the cabin.
I saw an article in USA Today a few years ago on this. Contrary to popular belief the air in the passenger cabin is circulated more frequently than generally thought. The air, as you stated, is quite cold at high altitudes, but the outside air is pulled into the aircraft through small vents. It is then heated by the heat generated by the engines to bring it to a comfortable temperature. The pilots can then control the temps by permitting more engine heat to heat up the air to the desired temp.
Usually thru bleed air systems coming off of an engine. This is routed thru ducts and transfers heat at an exchanger to carry the now warm fresh air to cabin.
Bryan is correct, The turbine engine has a bleed air system that siphons off some of the hot gasses from the combustion section (hot section) and runs it through a heat exchanger to heat the cabin air.
The customer bleed air as it is called is bled off the engine compressor section only. Never the combustion section. There is no need to heat this bleed air as the heat from the compression process brings it up to over 400-500 F already. After that it normally goes through a heat exchanger and then to an Air Cycle Machine which mixes the air and heats / cools the cabin as needed.
