點解飛機在零下40幾度的高空飛時不會結冰?

some informations below maybe help to the people who wish to know (copy & paste from Boeing B747s' Aircraft maintenance manual):

The Anti-Ice System is the system which prevent ice formation on critical areas of the airplane and aid the pilots when flying under ice and rain conditions:
(1) Wing Thermal Anti-Ice
(2) Engine Nacelle Thermal Anit-Ice
(3) Pitot-Static
(4) Total Air Temperature and Angle of Attack Sensor Anit-Ice
(5) Engine PT2/TT2 Probe Anti-Ice
(6) P2.0/T2.0
(7) Flight Compartment Window Anti-Ice
(8) Windshield Wipers
(9) Windshield Rain Repellant
(10) Windshield Washers
(11) Water Line and Waste Drain Heaters
(12) Ice Detection

The wing thermal anti-ice (TAI) system prevents the formation of ice on the leading edge of the wings. The wing anti-ice system receives regulated hot air from the bleed air pneumatic manifold

The flow of hot air to the leading edge is electrically controlled by a switch in the control cabin, which opens and closes a pneumatic valve in each wing. When the valves are open, hot air flows through ducting behind the wing leading edge.

我想空氣中的水份不多, 而空氣與機身摩擦產生高溫, 有水都蒸發了。