I’ve done super chilled pure water(like cooling undisturbed bottled water well below freezing). When you agitate it or open it, it freezes quickly. Not instantly though.
I’ve also thawed cold window glass with my breath and then watched ice crystals grow. That is pretty, but a bit slower. Even at -30 Celsius.
So what is the fastest it can freeze? I presume there is some latency of some sort involved. The speed of freeze. At -80, I could take a board sprinkled with droplets outside and it would take longer than milliseconds to freeze I suspect.
So lets design a linear test of some sort. How would we test and measure it? A long acrylic tube filled with purified water, super cooled? Then you tap one end with an hard object, and watch it propagate to the other end?
Assuming we rule out the possibility of the process leapfrogging the freezing fluid by transmitting something through and along the walls of the container, it seems like the upper limit for this is going to be the speed of sound in the medium being frozen - that’s usually the maximum transmission speed of any mechanical/physical process in matter.
I think getting rid of the enthalpy of fusion may be the limiting factor. As it freezes it’s going to evolve 79.92 calories per gram of ice formed. If that has no place to go it will slow down the change of phase.
I think there are 2 speeds here, the actual freezing of the water (very fast), and the propagation of the freezing disturbance (what you’re seeing), like speed of air molecule vibration and speed of sound. The vibration is like the freezing, being faster.
I don’t think you’d want to tap the end, since the sound could propagate faster than the freezing. Better to introduce a nucleation site, somehow. If you had a pan of supercooled water, you could lower an ice crystal onto the surface. You might have a different speed propagating along the water surface, versus through a volume of water, though.
AaronX, I’m not sure what you mean by the speed of the “actual freezing of the water”.
Perhaps OP means–and if not, I mean and would like to ask :)–when does the freezing of said molecules amount to a state where the water/ freeze displays a shear break at some macros state depending on mass and frozenhood chosen.
That coincides with what I noticed. I iceboxed a bottle of Doctor Pepper and when I opened it, the top half went slushy. Then it slowed or stopped. Once I poured half into a glass the other half iced up.
Right. I imagine the chemical reaction happens nearly instantaneously, but the growth of crystals is much slower.
If I wack a super cooled bottle on the counter, it should all ice up, but with a careful opening, the crystals have to propagate the freezing.
I mean the time taken for water molecules to assemble into ice.
Another problem (you may have noticed this when supercooling): freezing of supercooled water doesn’t result in a solid block of ice. It’s more like slush. So I don’t think the speed of freezing of supercooled water is the same as the speed of solid ice.
Maybe I’m missing something here but Cecil speaks about what freezes fastest but not what freezes first. Hot water should freeze more quickly than cold water but the cold water should still get to the freezing temperature before the hot water. My understanding is that it’s conceptually a bit like Zeno’s Paradox of Achilies and the Tortoise: Zeno's paradoxes - Wikipedia - although the actual relationship and maths behind it must be very different.
…where a cup of near-boiling water is thrown in the cold air and turns to ice almost instantaneously. If you instead threw a cup of cold water it would still be liquid when it hit the ground so in this case hot water DOES freeze first. I think what’s happening in the video is that the hot water droplets are so close to steam they break into fine particles which present a larger surface area and cool extremely quickly.
So basically, I don’t know anymore. This whole hot water turning freezing thing has confused the hell out of me. But my layman’s understanding is that hot water doesn’t freeze before cold water although it cools more speedily; however all bets are off if you greatly agitate the water when it is is near to boiling point. Someone please clarify this for me, or tell me if I’m wrong!
With all do respect to your master, he ain’t exactly correct.
In a previous life, I was a recreational vehicle mechanic. In the spring in would come the RV’s with broken copper tubing due to freezing temperatures. And it was always just the hot water pipes that were split open. Always had me a wonderin’. Years later I was in engineering classes and taking a large dose of calculus, when I discovered that water that has been heated will have a faster rate of change than water that has not been heated. Which is why only the hot water side on the RV’s had split pipes.
I really think you misunderstood something. There’s no way for water at a particular temperature to remember what it’s temperature was before.
Now heat loss goes up as the temperature difference goes up, so currently hot water in a cold place will lose more heat than cool water, but as the water cools down, the heat loss also slows down; there’s no ‘momentum’ or anything to it: heat loss depends only on the current temperature, not what it was before.
For the RVs, my best guess is that the hot water pipes were more corroded, so they split easier (or they tended to be made out of different material to begin with).
You are correct. Water doesn’t have a memory. But a molecular change happens when water has been heated, thus allowing it to have a faster rate of change.
cite:
the molecules in hot water, which is less dense than cold water, continue to move and in doing so cool quicker than cold water, which remains static.
What molecular changes? Nothing in your link, or in the actual paper which is here, say there is a molecular change to the water.
The paper actually say in its conclusion,“It therefore appears that the overriding conclusion is that circulation within the water is the primary cause in the differential between the rates of cooling that produce the Mpemba affect.”
That is true. It is also true that temperature is a macroscopic property - that is it is an average. If you have say a glass of water at 35F and you maintain it at 35F - all parts of the water will uniformly be at 35F. Now if you had a glass of water at 50F and you try to cool it in a refrigerator or in cold weather (without intense mixing) - the water near the surface/wall of the glass versus the center of the glass will be at different temperature when the average temperature cools down to 35F. The surface/wall of the glass will be conducive to form crystals while the bulk will conduct heat better due to higher temperature
Calcium carbonate precipitates out in water heaters. Also, most gasses have reduced solubility in water at higher temperature, so small bubbles could evolve from the water. Both of these will affect the freezing temperature of water, causing the hot water pipes to freeze first, even though both pipes are at the same temperature.
With all due respect, I did read your link. I also read (and linked to) the paper written by Adam Smith on which the entire article is based, titled “The Mpemba Effect: a three week study in the freezing effects of water.”.
Again, it is in the conclusion of this paper that it says, “It therefore appears that the overriding conclusion is that circulation within the water is the primary cause in the differential between the rates of cooling that produce the Mpemba affect.”
I can find no mention of a molecular change to the water in that paper.