Robin, I think you said this, but let me expand on temp vs.
pressure. As pressure decreases with increasing altitude, the
boiling temperature also decreases. ( the less pressure, the more
the water [air?] molecules can jump out of the water and escape
boiling). If we increase the pressure with a radiator cap (or in a
pressure cooker) it takes a higher temperature to boil.
The current way to also increase the boiling point of water is to
mix it with ethylene glycol. I don't believe this was available in
WW2 so they probably used water mixed with denatured alcohol (to
prevent loss by crew members)
Joel
They had glycol in WW II. In fact they tried pure glycol.
Trouble was the thermal conductivity of pure glycol was no where near
as good as pure water (few fluids are) so it was mixed with water to
improve the thermal conductivity.
Paul Lamar
I don't think the space between the molecules is filled up with air so
much as voids in the liquid.
Three issues here.. The temperature drops within the troposphere with
increasing altitude (up to about 35k MSL). The reduction in air
temperature helps the cooling system be more efficient. Interestingly,
the region between the top of the troposphere and the stratosphere is
characterized by essentially constant temperature (from about 35k MSL to
about 60k MSL, I think).
The lower density air at altitude means that the cooling system is less
efficient - fewer air molecules passing through the system to energize?
Can that be made up for by the increased true airspeed (the speed the
molecules are actually going when they enter the cooling plenum is
higher)? Does that suggest a particular plenum architecture for high
altitude flight?
The lower density air at altitude means that (above the critical
altitude) less energy is available to heat the system.
Matt-
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