Alcademics

I decided to measure the rate of freezing of an ice block in my (pretty crappy) freezer at home. It's just a standard apartment freezer. 

For all four times, I began with the same set of parameters:

• Igloo Legend 12 cooler
• 6 liters of cold tap water (this fills up the cooler a little more than halfway), in the freezer with the top off 

This is the typical set-up to make crystal clear ice slabs via directional freezing. 

Then I froze the water for 24 or 48 hours, setting the temperature on the coldest of warmest setting. 

I kept checking what those temperatures were, and found that there was a huge variation of temperature when set on setting.

• Warmest setting = 0F to 11F, average about 5F (-17C to -11C, average -15C)
• Coldest setting = -15F to 10F, average about 0 to -5F (-26C to -12C, average -17C to 21C)

The rates were

So if I want to make a slab of ice that is a little more than 2 inches thick, I can fill a cooler to 6L and leave it in for 2 days at the warmest setting. For me, this is ideal thickness to make big ice cubes. 

What is interesting here is that leaving the water in the freezer for double the length of time more than doubles the thickness of the slab, while we'd expect the rate of freezing to slow down. There is extra energy required to cool down the water to freezing temperature before it begins freezing, but most of the energy used should be in converting the water to ice. Perhaps this has to do with the insulated container, that cooling from one direction only is more energy intense than from all sides. Makes sense to me. 

Maybe I'll try 3 days to see how thick it gets.