The effect works best when there is a large temperature difference between your breath and the food or drink, so blowing on a spoonful of hot soup will be much more effective than trying to cool a cup of lukewarm water. You move your relatively cooler breath where the heated air used to be convection. Eventually, a cloud of vapor surrounds the food, which limits the ability of other water molecules near the surface to vaporize. Water molecules in hot foods and drinks have enough energy to escape into the air, changing from liquid water to gaseous water water vapor. Also, blowing on an ice cream cone will melt it more quickly. If you didn't blow on your food, the energy would be transferred to the surrounding container and air molecules conduction , causing your food to lose energy become cooler , while the air and dishes would gain energy become warmer. The limiting effect is mainly due to vapor pressure, which is the pressure the water vapor exerts back on the food, keeping water molecules from changing phase. Evaporative cooling is so powerful, it can even lower the surface temperature below room temperature.
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