Freezing Towel in Fridge

When I put a large glass container of water in our fridge it lets off a lot of condensation leaving a puddle on the top shelf it was sitting on. We were just wiping up the puddle every so often but decided it would be easier to put a towel under it instead. The towel does its job well enough but it actually freezes solid. My question is why. The water container is on the top shelf right at the front of the fridge. The only thing freezing is the towel.
- James (age 24)
Trevose, PA, US

That's an intriguing effect, and we aren't sure of the explanation. One possibility is just that the circulation in your fridge blows colder air on the shelf than on the region higher up. In our new fridge, the rear part is colder than the front. Most fridges have some sort of unevenness. Here's some evidence for that simple (boring?) explanation. Without the towel, water spontaneously relocates from the container to the shelf. That's an indication that something is thermodynamically different between those two places. The vapor pressure is lower on the shelf than in the container. In other words, it looks like the region of shelf is just colder. Maybe extra cold air is blowing past there, so that just above the shelf is even colder than the shelf, which has some thermal connection to other regions. That could make wet towel freeze even though the puddle didn't.

How to test that idea? One way would be to put a thermometer in, mounting it in various spots. Try to suspend it by a string so as to not disturb the airflow too much.

Mike W.

(published on 05/03/2015)