So spring is springing madly and it is time for the 6 monthly fridge/freezer defrost. I wrestle out the 3 icecube trays as I begin, only to find that they all have very little ice in them, full cubes after several months in pack ice have become mere shards. How is this so and why does the pack ice grow instead of evaporating under these same conditions?
I live alone and know I filled those trays completely whenever ice was used, I just haven’t used ice in months.
Your freezer has an automatice defroster and doesn’t distinguish between ice on the walls and ice in the trays.
I probably should have said whether it is frost-free or not. It is not, in fact this one is just a little bigger than a bar fridge with a tiny freezer in the top that controls the temperature of the whole 140 litres. That may have something to do with it perhaps. The pack ice takes over the freezer pretty quickly in it.
Sublimation.
Possibly, after time in the cooler, aggreggates in the chilled air sanded down the cubes. Just a WAG though.
Awe, barbitu8, you beat me to it!
Yep, sublimation.
I believe the answer is that the “pack ice” that forms on the freezer parts is forming on a part that is colder than the rest of the freezer. The ice cube trays are resting on a warmer surface, and/or are plastic and insulate the ice cubes from the frost forming around them.
It wouldn’t take much of a temperature difference for the ice cubes to sublimate, drift over and deposit on the freezer walls.
Actually, I don’t suppose that really helps much, does it? Sublimation is the process (if I recall correctly) of a solid skipping a phase transition and converting directly to a gas or vice versa. In your case, ice to water vapor. As to why it does that when the ice on the walls grows, here’s my guess.
Douglips is more or less correct. Air, even very cold air, holds water vapor. The warmer the air, the more water vapor it can hold. As your freezer sits there, heat slowly leaks in. Eventually, it warms up enough to kick the compressor on and cool it down again. BUT when the freezer is freshly defrosted, this means that the walls cool down very fast while your ice cubes stay at a slightly warmer temperature for a short while. This effect is probably compounded because your ice cubes are sitting in a plastic holder that acts as an insulator.
So, as the air circulates it cools off near the walls and drifts over your (slightly) warmer ice cubes. As your ice cubes warm the air, the relative humidity of the air goes down, thereby making sublimation (ice to vapor) more likely. As the now (relatively) warm and wet air drifts over the colder walls and cools down, the relative humidity goes up and the process is more likely to go the other way, i.e. vapor to ice. The net result of this process is that, over time, the ice cube slowly shrinks.
Don’t even think about asking about the math for this!
On looking at the thread, I can see that my answer might appear to be a dig at Crafter_Man. Totally unintentional. Apologies in advance.
Thanks for going to the trouble of answering this folks. I have a full size freezer as well so I will conduct an experiment and keep an ice cube tray in there and compare results in a few months.