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Old 07-27-2016, 10:42 PM
watchwolf49 watchwolf49 is offline
Join Date: Dec 2009
Location: State of Jefferson
Posts: 7,390
Originally Posted by Machine Elf View Post
The ambient air will have to be very dry. According to the standard psychrometric chart, 90F air at ~12% relative humidity will generate condensation if cooled to 32F. So if your ambient relative humidity is more than 12% at 90F, then you're going to add moisture to your ice cream sandwich, rather than drying it out. There are places with humidity that low, but they're relatively rare.

If the AC's evaporator is only cooling the air to 40F, then it's not drying it out enough to prevent condensation when it's further cooled to 32F. Hope you like soggy ice cream.
You may be going the wrong direction here. Let's assume the air coming out is 40F and at 100% RH. The air will start immediately mixing with the 70F air, the two will have a temperature above 40F, which means the RH of this mixed air will be below 100%. Evaporation will occur, and even if the air is then 100% RH, it is immediately push downstream being replaced by more air below 100% RH.

I understand you point, however it's invalid with the A/C unit. Even if our original air is 90F at 100% RH, the output will be 40F and 100% RH. The extra water condenses in the A/C unit and drains out the piping provide for this, not on the surfaces where the cooler air is going.

That doesn't mean the water is rapidly evaporating after it melts, and I have been specifying that this all depends on the RH. If the air is indeed leaving the A/C unit at 100% RH, then we may well see the melting first and not notice the evaporation. However I'm taking the OP at face value where we have a car full of young ladies exclaiming "It's like totally not melting". I'm only suggesting under certain circumstances this can be explained as I have above, The water melts but then quickly evaporates giving the impression that it's staying frozen, when it's actually "sublimating" instead.

One thing for absolute sure, ice cream in a 40F air flow will not stay frozen.

Last edited by watchwolf49; 07-27-2016 at 10:46 PM.