Originally Posted by Freemasm
“2. As others noted, most of the cooling is due to the evaporation of fuel.”
I’d 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.
Evaporation of liquids is a very powerful cooling mechanism - that’s how most air conditioners work. As you point out, carb ice is a problem with the throttle closed - when air flow thru the venturi, and hence adiabatic cooling, is minimal. What happens is most of those fuel droplets hit the closed throttle plate, and evaporate right then and there, not spread out thru the induction system. Also, you might note that many (most?) fuel injection systems use a venturi to sense the air flow, but almost none of these systems have a ‘venturi heat’ system.