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Q & A: slowly freezing ice cubes

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Most recent answer: 02/16/2017
Q:
I regularly freeze large ice cubes for my bar, and the strangest phenomenon has been occurring. It is taking 2 full days to freeze the cubes. They are 2 inch x 2 inch cubes in silicone molds, 6 and 8 cubes per mold, in an upright commercial freezer at -4 farenheit. There are 8 silicone molds total. The water I'm using is bottled, Earth 2o brand, begun at room temperature. The molds are stored together in either a stainless steel pan with a lid, or a plastic container with a plastic lid. I cannot, for the life of me understand why it's taking so long to freeze. Can you offer any suggestions?
- Joshua (age 41)
Portland, OR, USA
A:

There are basically two possibilities. Either it's taking an unusually long time to cool the water (poor air circulation?) or the water isn't freezing until it gets much colder than 0°C (32°F), i.e. it's supercooling. (See http://van.physics.illinois.edu/QA/listing.php?id=1618, http://van.physics.illinois.edu/QA/listing.php?id=1618

)My guess is supercooling. Here's an experimental test. Wait one day, so that the water should probably be below 0°C, but would take another day or so to freeze at your current rate. Then drop a little flake of ice in. Does it quickly turn to slush? If so, it's supercooled. If not, it was just cooling very slowly.

Mike W.


(published on 02/16/2017)

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