A commenter suggested that a glass of water left in a fridge would evaporate.

I couldn't tell if this is true. I don't want to do the experiment since it would take too long; so I thought instead I'd ask here.

Assume 1 cup (237 ml) of water in a typical cylindrical glass; the fridge is at 4C. Assume the fridge is never opened for the duration of this week. For "extra credit"*, assume the fridge has 640 lt volume, resides in a room at 25C and 50% humidity, and is opened 5 times a day.

*: No, it's not a homework question, hold your close flags.

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    $\begingroup$ Possible duplicate of Is air in the refrigerator dry? how much? $\endgroup$ – James Rowland Jun 22 '16 at 4:50
  • $\begingroup$ Why not try to do the experiment with a smaller quantity of water? $\endgroup$ – valerio Jun 22 '16 at 6:26
  • $\begingroup$ Ice in a freezer will evaporate. If your chicken breasts / burgers / steaks / etc aren't well wrapped, they end up freeze-dried. $\endgroup$ – John Duffield Jun 22 '16 at 11:46
  • $\begingroup$ Hi Superbest. If you haven't already done so, please take a minute to read the definition of when to use the homework-and-exercises tag, and the Phys.SE policy for homework-like problems. $\endgroup$ – Qmechanic Jun 22 '16 at 18:37

Evaporation depends on vapor pressure of environment. If vapor pressure inside the fridge is lower than saturated pressure of water at $4^\circ C$, then the water will vaporize.

  • $\begingroup$ I think that even if at the saturated vapour pressure the amount of water in the glass might change as water might condense elsewhere in the fridge? $\endgroup$ – Farcher Jun 22 '16 at 7:51

Yes, of course it will. You probably already know this.

  1. If you leave food uncovered for too long in the fridge, it dries out. If you have never noticed this for yourself, you are too hygienic and well-organized. Loosen up.

  2. If you leave ice cubes uncovered in the freezer for a few months, they dry out, leaving limescale. If you have never noticed this for yourself, drink less whisky.

And yes, it is partly to do with different temperatures in different parts of the fridge. The cooling coils (and the fridge wall next to the cooling coils) will be either (when not cooling) at the same temperature as the rest of the fridge or (when cooling) much, much colder. So there will be a constant migration of moisture from everywhere else onto the coils.

  • $\begingroup$ And now I know how the exposed coils at the top of my fridge sometimes have a frozen drop or drip water. Thanks, $\endgroup$ – Regular Joe Jul 13 '18 at 19:41

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