Less chance of carby ice at higher levels of relative humidity?

[Romeo Juliet Whiskey]

Its interesting when studying the Carburetor Icing Probability Chart that the probability of icing at some point of relative humidity decreases as humidity increases. In fact, if its 28 degrees outside, we are on decent and the relative humidity is 50% then we have a moderate to serious carby ice. If the relative humidity suddenly jumps up to 90% then there is only a chance of light ice.

 

I was under the impression that the higher the relativehumidity, the more probability there is of carby ice? The CASA probability chart says otherwise.

 

 

[facthunter]

Doesn't make sense to me. There is a greater amount of ice possible with more (absolute ) moisture content. Higher temps permit more water to be held at any given RH, but it's getting further from the zero degrees required to form ice, in the carb which can easily be less than ambient. Water forming ice undergoes a change of state, similar to water vapour going to water drops, so there may be some heat involved there, affecting the total picture. Nev

 

 

[mnewbery]

http://www.atsb.gov.au/media/56519/carb_icing.pdf

 

http://www.mrc-eng.com/Downloads/Moist%20Air%20Props%20English.pdf

 

 

 

The point of the ATSB document is that there is so much water in the air at 28C and 90% RH that it is unlikely but still possible to reduce the temperature to where icing occurs

 

 

 

Specifically at 28C and 90% RH the coefficient is around 75 Kilojoules per kilogram of humid air per degree drop/rise. At 50% RH that number drops to 60 KJ/Kg/Degree.

 

 

 

Much easier to cool to zero with only a little water and a little temperature.

 

 

[Romeo Juliet Whiskey]

http://www.atsb.gov.au/media/56519/carb_icing.pdf

http://www.mrc-eng.com/Downloads/Moist Air Props English.pdf

 

 

 

The point of the ATSB document is that there is so much water in the air at 28C and 90% RH that it is unlikely but still possible to reduce the temperature to where icing occurs

 

 

 

Specifically at 28C and 90% RH the coefficient is around 75 Kilojoules per kilogram of humid air per degree drop/rise. At 50% RH that number drops to 60 KJ/Kg/Degree.

 

 

 

Much easier to cool to zero with only a little water and a little temperature.

That makes sense... Cheers!