3 ms·

I got into this rabbit hole once and remember having the same thought, I checked some paper and they used the same mass as measured when putting water into the

by comboy 4y ago

I got into this rabbit hole once and remember having the same thought, I checked some paper and they used the same mass as measured when putting water into the freezer. AFAIR it was also tight, closed container so evaporation shouldn't have a big impact (checking mass after sure seems like a good idea). Intuitively hot water should be much slower to freeze. It takes quite a bit of time for it to get to the same state that the cold water is at the start. After that time, the way we look at it, it's at the same point in experiment as if we have just put the colder water in. So we seem to still be missing something.

Tuna-Fish 4y ago
> After that time, the way we look at it, it's at the same point in experiment as if we have just put the colder water in. So we seem to still be missing something. Unless there is very substantial mixing, the container of hot water will never be at the same state as the container of cooler water. We did this in high school, with 3 open-topped 10L buckets, one with 25C water, one with 95C water and no mixing, and one with 95C water sitting on a magnetic mixer. They were not in a freezer, but outside at ~-25C. The freezing order was 95C unmixed, 25C, 95C mixed. We also had a few temperature probes in the 95C unmixed bucket, and found that about halfway through, the temperature of the water in the middle about 1/3rd of the way from bottom was sitting at 0C, while the temperature of the water at middle at the top was still >70C. Our final findings were that: 1. The buckets cool mainly by evaporation, which is only happening at the top, and which is much faster for hotter water 2. Water of different temperature stratas can be surprisingly stable even in a small container 3. In the unmixed bucket a stable, slow flow of water down the sides and up the middle forms. New hot water emerges from the middle, gets cooled and pulled to the sides, and then pulled down to the bottom. This circular flow is probably caused by the fact that water at the sides get initially cooled a bit and so it sort of biases the flow. But now there's people saying it still works with closed-top containers, so I dunno. My physics teacher clearly did this every year and knew what was going to happen. The class came up with those findings after some very specific questions by him.
- comboy 4y ago
  Very cool finding with the flow. It explains why when you take some round container and freeze water in it, the ice will be crystal clear at the edges, but it will not be crystalized so cleanly in the middle (turbulence once edges are frozen) Who knows, perhaps there's even some laminar flow happening at the edges :)

by comboy 4y ago

Tuna-Fish 4y ago

> After that time, the way we look at it, it's at the same point in experiment as if we have just put the colder water in. So we seem to still be missing something. Unless there is very substantial mixing, the container of hot water will never be at the same state as the container of cooler water. We did this in high school, with 3 open-topped 10L buckets, one with 25C water, one with 95C water and no mixing, and one with 95C water sitting on a magnetic mixer. They were not in a freezer, but outside at ~-25C. The freezing order was 95C unmixed, 25C, 95C mixed. We also had a few temperature probes in the 95C unmixed bucket, and found that about halfway through, the temperature of the water in the middle about 1/3rd of the way from bottom was sitting at 0C, while the temperature of the water at middle at the top was still >70C. Our final findings were that: 1. The buckets cool mainly by evaporation, which is only happening at the top, and which is much faster for hotter water 2. Water of different temperature stratas can be surprisingly stable even in a small container 3. In the unmixed bucket a stable, slow flow of water down the sides and up the middle forms. New hot water emerges from the middle, gets cooled and pulled to the sides, and then pulled down to the bottom. This circular flow is probably caused by the fact that water at the sides get initially cooled a bit and so it sort of biases the flow. But now there's people saying it still works with closed-top containers, so I dunno. My physics teacher clearly did this every year and knew what was going to happen. The class came up with those findings after some very specific questions by him.

comboy 4y ago
Very cool finding with the flow. It explains why when you take some round container and freeze water in it, the ice will be crystal clear at the edges, but it will not be crystalized so cleanly in the middle (turbulence once edges are frozen) Who knows, perhaps there's even some laminar flow happening at the edges :)