If you froze a glass of water in your freezer and found that the ice disappeared, it is likely due to a process called sublimation. Sublimation is when a solid (like ice) transitions directly into a gas without passing through the liquid phase. In the context of your frozen glass of water, the ice may have sublimated into water vapor without melting first.
Here's what might have happened:
Low Humidity in the Freezer: Freezers are designed to maintain very low temperatures, typically well below the freezing point of water. At such low temperatures and with low humidity levels, the frozen water in your glass may have started to sublimate directly into water vapor, rather than melting into liquid water.
Porosity of the Ice: The ice's porous structure can also contribute to sublimation. The surface area of the ice exposed to the dry freezer air increases due to the porous structure, facilitating the direct transition of ice to water vapor.
Time and Temperature: The process of sublimation is gradual and may take some time to become noticeable. If your freezer maintains a consistently low temperature, the ice in the glass will eventually sublimate over a longer period, leaving the glass dry without any visible liquid water.
The presence of the penny on top of the ice might have contributed to a faster sublimation process. The metal penny could have conducted heat more effectively and created small areas of slightly warmer temperature on the ice's surface, enhancing the sublimation process.
It's important to note that sublimation is a natural process, and over time, any ice left exposed to a dry environment can undergo sublimation. This is why, in some cases, ice cubes in the freezer may shrink in size even if they are not used for an extended period.
If you want to test if your freezer has defrosted at any time, you might consider using other methods or indicators that are not prone to sublimation, such as checking for any thawed or refrozen food items or using a temperature data logger to monitor temperature fluctuations.