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Old 01-20-2021, 03:08 AM
Cumulo Cumulo is offline
Join Date: Apr 2015
Location: KHMT
Posts: 76
Default isentropic vs adiabatic expansion?

Originally Posted by Freemasm View Post
2. As others noted, most of the cooling is due to the evaporation of fuel.

Id need more data but with a lack of such, this seems doubtful. Low local static pressure levels seem to be the prime driver. Example: Axial Compressors ice at very high ambient temps when inlet guide vanes are less than full open (no fuel evaporation effects). Likewise, carb heat is rarely needed at power levels greater than 80% i.e. throttle valves open/low static pressure loss. Similarly, closed throttles (resulting low local static P added to that of Venturi) where very little fuel flow (very low latent heat losses) are most prone to icing for given conditions.

If someone has related data, it would be appreciated. As of now, I would need some convincing.


Expanding a gas through the blading of the inlet guide vanes of an axial compressor, which was one of your points, could possibly produce much more cooling effect than a throttle process..
I suggest that that process will be adiabatic and produce a lower temperature that a throttling process will. I am less certain about the difference compared to the carburetor venturi though.

I don't have the numbers for the relative effect of expansion vs latent heat of fuel, but I suppose some one could grind it out using the different ratios.

Learned to fly in Michigan in the winter and early spring in my then C65 Champ nearly seven decades ago. It was stick/throttle/carb heat most days. Carb icing was expected and pretty much ho-hum. Later, early Bonanzas with PS-5's, a dry carburetor with the fuel introduced down stream, no icing. So, I would have to guess that the temperature drop from fuel evaporation is the more important factor. But again, no numbers.

Something related to fuel cooling effect: In Libia in WW2, the standard beer cooler was an empty drum, usually delidded with prima cord, filled with beer bottles and avgas, then bubbled with an air hose. Presto, cold beer due to the latent heat of gasoline. And that is how to win a war.
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