Heating in Blackhawk.
Hi Hedncld. Your question regarding the temperature rise of the bleed air is relatively easy. The temperature rise is due to the air being compressed. Just think of how a diesel engine works. There are no spark plugs (some have "glow" plugs to initiate ignition at start-up) in a diesel. In fact, they are sometimes called "Compression Ignition" engines because they run at very high compression ratios, 18-22 : 1 is common, which causes sufficient temperature rise to ignite the fuel/air mixture.
The heated air from the bleed air system would be far too hot to be ducted direct to the cabin of the Blackhawk, so it probably goes through an air to air heat exchanger and then into a mixing plenum where it is mixed with ambient air at the appropriate ratio to have air at the desired temperature ducted into the helo. There would be some friction induced temperature rise in the air passing through the engine compressor, however the major temperature rise is due to the effects of compressing the air.
By the way, ACM's are used to reduce air temperature in many aircraft, the B707/B747 being typical examples.