General > General Technical Chat
Freezing Speed of Hot Versus Cold Water
bdunham7:
--- Quote from: dunkemhigh on February 25, 2022, 06:42:07 pm ---Well, presactly. That's the problem, isn't it? And you not only have to determine that freezing has occurred, but when it occurred.
--- End quote ---
That is a problem with a pretty well established and accepted solution. Freezing is complete when the temperature starts dropping again at the end of the plateau. If that is a sharp curve, you know the point fairly precisely from graph of your data points. But if you terminate the experiment at 0C, you can't possibly pinpoint the time when the water is completely frozen, at least not with a graph of temperature.
PlainName:
--- Quote ---Freezing is complete when the temperature starts dropping again at the end of the plateau.
--- End quote ---
When your temperature probe drops you know the entire volume is frozen? Not just the part that your probe is embedded in?
IanB:
From an experimental point of view it is important that the sample is in a completely uniform state at the beginning and end of the experiment, so that its internal properties are everywhere the same. A practical way to achieve this is to have the sample well mixed. If you allow the sample to freeze, it becomes impossible to have it well mixed, and therefore impossible to know when it is uniformly frozen. For this reason, experiments should not allow the sample to freeze. They should go from liquid at one temperature to liquid at another temperature.
PlainName:
--- Quote ---For this reason, experiments should not allow the sample to freeze.
--- End quote ---
I know what you're saying. Just thought it was funny, given the context 8)
bdunham7:
--- Quote from: dunkemhigh on February 25, 2022, 08:08:37 pm ---When your temperature probe drops you know the entire volume is frozen? Not just the part that your probe is embedded in?
--- End quote ---
That's an issue for some experimental finesse and probe placement, but the general theory is that the temperature remains constant until the whole thing is frozen because any remaining liquid is still rejecting heat as it freezes. OF course any real physical sample will have a gradient, but nobody said experimental physics was easy, even for simple things. But this is not some new thing I'm proposing....
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