Soup bowl effect

The soup bowl effect. Suppose we gently stir a bowl of soup with a spoon so that the soup revolves around the bowl. If the spoon is lifted out of the soup (i.e., the energy source is removed), the... 

The first effect is illustrated when we blow across a bowl of hot soup, to cool the soup. Our breath displaces the steam vapors that are on top of the soup. This encourages more molecules of steam vapors to escape from the soup that is, the vapor pressure of the steam above the liquid soup is diminished, because steam is pushed out of the soup bowl with air. The correct technical way to express this idea is to say, The partial pressure of the steam, in equilibrium with the soup, is diminished. But our breath itself does not remove heat from the soup. The evaporation of steam from the soup, promoted by our breath, takes heat. Converting one pound of soup to one pound of steam requires 1000 Btu. This heat of evaporation comes not from our breath, but from the soup itself. The correct technical way to express this second effect is, The sensible-heat content of the soup is converted to latent heat of evaporation. ... 

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