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Freezing Speed of Hot Versus Cold Water
bostonman:
--- Quote ---re: "...maybe this was already confirmed or rejected...my understanding is that the greater the temperature delta, the quicker something will change..."
Yup, confirmed by various replies by multiple people already.
--- End quote ---
I read these messages more thoroughly than now that I had time to devote in front of the computer (sometimes I scan the messages on my phone while out so I have time to process what is being explained).
I think the answer was provided by methods of more wording within explanations, but at least it confirms my initial understanding of the larger the temp delta: the greater the temp delta the quicker it changes and slows as it gets closer to the other object (room temperature in this case as per my previous example).
Maybe for a moment we should forget about actual freezing because the physics behind ice is more complex than I thought. I'll openly admit, I wanted to keep the data going for much longer than what my graph shows. Once I saw the outside temp was about 25 degrees F and expected to drop, I realized this could be my one last opportunity before winter passes to conduct this test, however, I expected the water to freeze much quicker. Due to thinking it would freeze quicker, I set up my area in an inconvenient location and in open view mid-afternoon. Once it turned night, I feared if I kept things setup throughout the night, animals might disturb things and/or someone may see the setup and enjoy two free saw horses (not that I live in a bad area, but someone did steal my garden hose and reel one year).
In any case, I made the assumption that seeing "ice", and 32 degrees F on the meters, was enough data to conclude what happened. Everyone is correct and that the tins weren't a solid chunk of ice (but they were quite solid), but my conclusion at a gross level was: hot water and cold water both reached "32" at nearly the same point (again, let's forget about actual freezing for a moment).
The other portion of my conclusion: If I had friends coming over and was out of ice cubes for drinks, starting off with hot water isn't going to provide ice cubes significantly quicker than plan old cold (tap) water. What I also knew before the experiment: if I place hot water in my freezer, I'm going to heat the freezer thus making the freezer work harder. Obviously this is why I conducted my experiment outside as one tin of hot water isn't' going to rob the Earth of cold.
Another reason I removed the test rather than keep it into the night: I knew many portions of my setup weren't ideal. As someone pointed out, multiple temperature probes placed in various areas would be ideal and all probes in the same locations in both tins; but also, the plywood the tins sat on were a heat sink, the data loggers aren't perfect, etc...
I expected to see a significant difference in temperature once one of the tins got close to 32, maybe something like the cold was 38 and the hot was 32 and it was clear hot or cold "freezes" faster than the other. Once I saw both tins had a significant amount of ice and it seemed both tins got there at nearly the same time, I figured at a gross level, I concluded hot versus cold have little affect on how long it takes to freeze.
Maybe my statement of using "freezing" was overboard. At a common sense level, I realize water doesn't always freeze as expected and at exactly 32. Now that I've read some technical reasons, I have a better understanding why. Having said this, it was probably wrong to to use absolute statements like "froze".
Based on my graph, and leaving out that my tins weren't technically "ice", I feel both reached an end point nearly the same time. Now at an atomic and physics level, and water impurities, I can't make any serious conclusions on which actually froze (and froze solid) quicker.
This experiment is from something that occurred years ago. My friend needed ice cubes and used hot water telling me hot water freezes faster. Over the years I've kept wanting to conduct such an experiment.
I think it's safe to say, if I have a friend that tells me using hot (tap) water is going to provide ice cubes much quicker, I know this will not be the case.
Siwastaja:
--- Quote from: bostonman on February 20, 2022, 05:11:06 pm ---but my conclusion at a gross level was: hot water and cold water both reached "32" at nearly the same point
--- End quote ---
But this is what I really struggled to understand. Like, are we looking at the same graphs? Because the graph you posted shows the cold one reached 32F at 17:15, and the hot sample at 18:15, roughly. Seems a big difference to me!
bostonman:
Oh, I understand your statement now.
You're correct, the cold water is 32 F sooner than the hot. I still feel due to many factors, it's close enough to conclude at a gross level you can't gain freezing time from starting off hot or cold.
But yes, you are absolutely correct, the hot water was still hotter than the cold and therefore took longer to "freeze"; clearly an error on my verbal statements versus the graph.
edit: I attached an expanded section of the graph
Siwastaja:
It could even be that the hot sample starts freezing as late as 19:10 or so, it's hard to say!
Mentally shift the red graph up by 0.25F (assuming sensor offset error, or small differences in mineral content) and you see what I mean: doesn't it replicate what the cold sample did earlier, even including that interesting "overshoot" which bumps back up again? (Someone more familiar with small-scale effects not well explained by the simple equations could comment whether those overshoots and bouncebacks are actual, or measurement artifacts.)
BeBuLamar:
Assuming the outside temperature is constant. The initial cooling rate of the hot water is faster but it's hotter so it has to cool down to the same temperature as the cool water at which time the rate of cooling is the same as the cool water when it started but now the cool water is cooler. So no you do not see the hot water reaches the outside temp before the cool water.
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