On 9/5/2021 at 8:23 AM, JoNorvelleWalker said:As much as I respect the great minds, I call balderdash. I maintain blowing on soup cools it primarily by the Joule-Thomson effect, in which a gas is cooled by being forced through an orifice, eg. one's lips. This is easy enough to prove with an experiment: with mouth open, blow on soup with all one's might. Keep blowing, because you will be at it quite a while.
As a rule of thumb, you'll achieve ~0.25 K/bar JTE when decompressing air. Assuming that you are unlikely able to create more than 0.1 bar overpressure in your mouth, that amounts for 0.025 K of temperature decrease when blowing. It is unlikely to cause a significant effect to soup.
On 9/5/2021 at 8:23 AM, JoNorvelleWalker said:Then purse your lips, as one naturally does when cooling soup, and continue blowing. The soup cools quickly. The experiment does not need soup, or even a thermometer. With mouth open blow on your hand. Your breath feels warm. Purse your lips and continue blowing. Your breath feels cool.
Funny enough, the reason for that is that the superficial moisture on your hand gets evaporated faster by the stronger blow through your pursed lips. The heat of evaporation of water is magnitudes larger than the JTE ...
So, all in all, both guys seem to be in line with the current themodynamic theory ...
