Controversy continues over whether hot water freezes faster than cold
quantamagazine.org
quantamagazine.org
Also, if some of the water starts at 100°C, then presumably some of it will evaporate, and one should measure how much remains... The article does mention this possibility, though it doesn't evaluate or quantify it.
In theory you could also go by number of particles (measured in mol).
If it's 'yes this does happen, why?' then it seems right to try same mass, to test that theory.
Under controlled conditions, it would not. Ideally it would be in a pressure regulated space.
That probably wouldn't do much to help us answer the question of what will happen in our own freezers which aren't pressure regulated. While I'm glad there are and will continue to be all kinds of investigation and exploration around the Mpemba effect what I (and many others) really want to know is if heating water first would help with real world situations like having ice cubes ready in time for an event.
I can accept that it might not always be the case, but considering that at this point we can't say for sure if the effect is real at all it'd be nice if we could get it settled that it worked often enough and potentially decreases freezing time enough to be worth the time and trouble of microwaving our ice cube trays even if all the details and underlying mechanisms aren't well understood.
I should probably just start trying it myself and see what I come up with on my own, but even imperfect lab experiments would be much more accurate and trustworthy. I regularly do things like heat a mug full of water in the microwave, get distracted, and then forget all about it for hours.
If the mechanism is that 10% of the water evaporates away, allowing the remaining 90% to freeze smaller by virtue of its reduced mass, the take-away for making ice in a hurry is not to use hot water. It is to use cold water, but a little less of it.
Honestly, smaller ice cubes is probably your best bet if you need ice in hurry either way.
It would do a great deal to answer the question. Knowing the base physics (or at least the outcomes) then allows further experimentation and calculation to answer more complicated (less controlled) conditions.
> I regularly do things like heat a mug full of water in the microwave, get distracted, and then forget all about it for hours.
AFAIK, everyone does that ^^
A more mundane explanation is that hot water evaporates faster than cold, decreasing its volume and thus the time it takes to freeze.
[Edit - Cannot delete my comment now. As 'ketzo' points out below my point is not same as OP's. OP points out that hot water is less dense. Maybe less dense liquid cools faster]
That quoted sentence says that hot water loses volume compared to cold water.
The person you’re replying to is saying that hot water simply takes up more space as well.
- 1 m³ of hot water is less water (in terms of mass) than 1 m³ of cold water
- 1 kg of hot water has a bigger surface area than 1 kg of cold water
I am still not convinced that this alone would explain such a phenomena. I'd rather believe there is some weird fluid dynamics and layering involved.
The singular is "phenomenon".
The second less so. Hot water has a bigger surface area, which makes heat loss fast at first. When it gets to cold water's temp it should have the same surface area as the cold water making the advantage disappear.
> Water is a strange substance, less dense when solid than liquid, and with solid and liquid phases that can coexist at the same temperature.
> the Mpemba effect could happen through a related mechanism that Raz has previously described with Lu in systems that undergo a second-order phase transition, meaning that their solid and liquid forms can’t coexist at the same temperature. Water is not such a system (it has first-order phase transitions),
This is where BTUs come in handy..
Or is this effect unique to just water?
At the macro level, one can come up with ideas. Convection currents within the fluid, and in the air touching the fluid, maybe; though, say, once the hot water has cooled from 100°C to 35°C over a period of—what, ten minutes?—I'm pretty skeptical that there would be so much inertia in those currents that they'd persist, and persist strongly enough to accelerate the 35° to -1° cooling, enough to beat the head start of the water that started at 35°.
Maybe the initially cool water forms some uniform layer of very-cool water at the top (which, being very cool, doesn't exchange much heat with the very-cool air above it; an ice layer would be an example of this), which is held together by surface tension or something; whereas with initially hot water, that layer is not uniform and there's more mixing (and constantly-created convection as a result)? I have no idea if any of that is realistic. If so, it would suggest that shaking a cup of cold water (perhaps after a few minutes in the freezer) would work as well as having it start hot.
... After writing the above, I saw that (a) infogulch below has the same idea, (b) Wikipedia has an anecdote appearing to confirm it[1], and (c) the article doesn't seem to mention shaking, stirring, or otherwise agitating the cup.
[1] The Scottish scientist Joseph Black investigated a special case of this phenomenon comparing previously-boiled with unboiled water;[9] the previously-boiled water froze more quickly. Evaporation was controlled for. He discussed the influence of stirring on the results of the experiment, noting that stirring the unboiled water led to it freezing at the same time as the previously-boiled water, and also noted that stirring the very-cold unboiled water led to immediate freezing. https://en.wikipedia.org/wiki/Mpemba_effect
I'd be curious to know if the defect remains while stirring until frozen.
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.
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.
Who knows, perhaps there's even some laminar flow happening at the edges :)
Introducing hot water into a freezer rapidly raises the ambient temperature of the freezer. This causes the thermostat to click on, and the heat pump therefore runs until the ambient air drops down below the thermostat's shut off point. A lot of heat is removed very early on, and the ambient freezer temp is at its lowest going into the liquid to solid phase change.
With the cold water, the ambient air of the freezer doesn't rise nearly as much. The thermostat does n't click on until a long while later, once enough heat leaks out of the freezer. The ambient air is warmer going into the phase change.
It doesn't work if you put the two cups in the same freezer, but at least it could explain some anecdotes.
Near boiling water is about 4% less dense than near freezing water. If you filled the buckets right to the top, there would be less water in the hot bucket.
I don't know if I'd call it trivial, bringing 1 kg of water from 85C to 0C involves about 100W for a duration of one hour whereas a typical freezer removes heat at, what, 200W or 300W?
That looks like the amount of energy needed to heat that water.
But cooling things doesn't work the same way. Instead you want to extract that energy/move it somewhere else. The efficiency of some approaches, unlike when heating something, can hugely depend on ambient temperature. It's possible you'll be able to extract more useful energy cooling something than you'll have to expend!
This may happen but, in a normal freezer, the action of the compressor is meaningless.
My feezer is 70% full, with probably 30kg of stuff in it. This stuff is mostly at -22C (I have a thermometer), and so, this mass is what cools new things added to the freezer, fast.
(Why -22C instead of -18C? Salt water fish is in there, and I also want a little headroom.)
For example, most manuals urge one to not have an empty freezer. That cold mass is one reason why.
When I was a kid, we had a fridge from the 50s in a cottage. When I started drinking, we'd put 5 cases of beer (24*5) in glass bottles in there, and 2 hours, yes hours later they'd be at 1C.
Now, modern fridges/freezers literally do not have that degree of cooling power. This is on purpose, for it is more efficient to power a small compressor all the time, than a massive compressor for 10 minutes.
You may want to argue this point, and that's fine, but I am merely providing info both from the manuals of modern freezers and fridges, which I have read, and from online when looking at why they are so bloody slow to cool things.
My LG fridge manual actually says not to put warm meat in my freezer, unless the thing has loads of frozen stuff in it.
Otherwise the meat could go bad before freezing.
Oh, another wonder of modern fridges. If you buy one and put it outside, or in an unheated garage, the freezer becomes useless.
This is because many fridges have no thermometer in the freezer part, and only get a reading when the compressor comes on, to cool the fridge.
As the fridge is always cool when it is 3C outside, or cooler, the freezer never keeps stuff frozen.
> My LG fridge manual actually says not to put warm meat in my freezer, unless the thing has loads of frozen stuff in it.
That sounds silly to me. In my experience ice cubes freeze within an hour and meat within a couple hours.
> “We all have this naive picture that says temperature should change monotonically,” said Raz. “You start at a high temperature, then a medium temperature, and go to a low temperature.” But for something driven out of equilibrium, “it’s not really true to say that the system has a temperature,” and “since that’s the case you can have strange shortcuts.”
I gotta admit, that's pretty cool and unintuitive.
It's found it's way into the "minimal valley" whereas an arbitrary lukewarm state might be closer to a "ridge".
Clearly, yes, if you could start at the magic state that would be ideal. And there should be experiments that use a bunch of thermometers too compare the time from the same average temp (the initially warmer one just gets the "running start").
Mathematically it is not hard to abstractly characterize what is going on. (This is not saying the actual physics is easy!!) Temperature is an equivalence class on fluid states, but the average time to transition between those states does not form a metric space. The failure of the triangle property shows that the composition of transitions induces non-uniform distributions within the temperature equivalence classes that subvert the expected transition time by which we had attempted to build a metric space to begin with.
Just like non-euclidian space in the 19th century, this is the sort of thing where the mathematics can say "yeah sure seems legit" before the physics stops saying "wait wtaf",
1. Temperature is monotonically related to energy content. A warmer system has more energy than a colder one, all else being equal.
2. To cool, a system must release energy. The rate at which a system can release energy is monotonically related to the difference in temperature between the cooling system and the cold sink to which its energy is being released. The bigger the temperature difference, the higher the rate of energy release (all else being equal).
For the Mbemba effect to be real, one of those two premises must be false. Which one is wrong?
In equilibrium, the temperature of the water is directly related to the energy content, with the heat capacity being the conversion factor.
But under the thermodynamic definition, the temperature of the system depends not only on its energy but also on its entropy. And one of the points the article is making is that even when we know the total amount of energy entering or leaving the system, its entropy may not be nearly so easy to measure or calculate when its state is far from equilibrium.
Let's say you're given a few hot potatoes and have to cool them down as fast as possible. You have a refrigerator but you can only keep one of them in it at a time. How do you decide which one to put in at any given time so they all reach temp the fastest? When the "system" involves many possible pairings of temperature differentials it feels very intuitive that some configurations would be better than others. So it removes the mind-bending thermodynamics law breaking aspect of it.
Admittedly, this isn't really what the article says! I honestly don't get how my above intuition squares with the whole energy minima thing, and so while useful as a thought exercise to at least help me entertain the idea, I'm not really sure it's correct?
It doesn't have to "learn" anything in order for there to be a substantial difference.
> The Scottish scientist Joseph Black investigated a special case of this phenomenon comparing previously-boiled with unboiled water; the previously-boiled water froze more quickly. Evaporation was controlled for. He discussed the influence of stirring on the results of the experiment, noting that stirring the unboiled water led to it freezing at the same time as the previously-boiled water, and also noted that stirring the very-cold unboiled water led to immediate freezing. https://en.wikipedia.org/wiki/Mpemba_effect
I'm surprised the article didn't mention this.
Very interesting!
Stronger convection means greater heat transfer, thus greater rate of cooling down.
But it'd be surprising if the inertia of the convection of the initially hot system didn't just gradually decline (because of friction) to almost exactly (little bit greater) the same level of convection (which the initially cool system had in the beginning) when it reaches the same average temperature.
That is, you could perhaps model the bulk of water as having a temperature field, and clearly every point in that field passes through the starting temperature of the initially-cool system, but the gradient landscape is vastly different.
Heat transfer, convection, conduction, evaporation and so on should be available in useful implementations in state of the art simulation software.
Because this is literally about the time-domain solution to heat conduction and fluid dynamics (convention) with different initial conditions and boundary conditions (shape of vessel, temperatures at boundaries, etc.).
For example if there isn't uniformity of initial temperature, if there isn't uniformed of the applied cold sink, if there isn't uniformity of heat flux capacity due to conductivity of the interfacing boundary conditions, etc. There's even questions about the water purity or contaminants which definitely would change the answer.
These are not and often can not be controlled. And in practice at home, you will never duplicate even what the answer is in a control lab experiment.
It is the norm to have a range solutions that entirely depend upon initial conditions and boundary conditions. And there's also uncertainty of even knowing the values of these conditions.
Expecting a simplistic yes/no answer to many problems ESPECIALLY those involving heat transfer and fluid dynamics is like asking for a specific date for your date from your date of birth or your childhood medical history.
See also climate change - we DO NOT KNOW there is a specific date when things "tip" and ANYONE claiming there is a date let alone timeframe is a liar or so ignorant they can't possibly be right! The error of any model is larger than the estimate value itself.
You'd think people would have learned something from the 20th century about the FACT that we do not live in a 19th clock-work universe with complete predictability. We know how it can never be predictable especially if fluid dynamics is involved - you know, mathematical chaos and all.
Both means yes. It's pretty clear that in some circumstances cold water freezes faster. The interesting thing is whether hot water EVER freezes faster.
Some years ago, I kept chickens here in Michigan through the winter. I wanted to leave them with access to water while I was gone at work, but after filling the tank in the morning, I'd often come back to a block of ice and thirsty chickens in the evening. My experimental procedure was as follows: On a Saturday when I'd be home all day, I filled two identical 5 quart poultry waters to the same level, one with 115F hot tap water and one with normal 47F cold tap water. Both came from our well, from a sink with an aerator, and both passed through a softener. The hot water had been heated in a tank-style residential water heater, not over the stove. The troughs were left outside of the coop in a shed (several feet apart) to prevent unpredictable chicken activity from messing with the results. I put thermocouples in both troughs and checked in every half hour to take readings.
The hot water froze first by several hours!
The cold one reached 32F first, and after hitting 47F the rate of change of the one that had been hot was similar to the cold one (maybe slightly faster, but my measurements were too coarse to be confident of that), but both spent quite a bit of time at exactly 32F. The hot one just spent so much less time at 32F that the couple of hours to drop to 47F didn't matter. Both still had a considerable volume of liquid water in the bulk tank, the part exposed to air froze first, but that's still a failure because the chickens couldn't drink. I didn't have any equipment to measure dissolved gasses in the water, or measure convection or stacking in the tank, measure the rate of evaporative cooling, measure the rate of cold air being pulled over the surface by convection driven by the hot water temperature differential, or otherwise test any other factors that might be different from two apparently identical 32F tanks of water, all I knew is that the hot water froze faster.
The result of the experiment was just to put a small electric heating adapter under the base. After that it didn't matter. Another tragic example of pragmatism over curiosity...
For example, let's say you started with the hot water, and then let it cool to 47F--perhaps by putting it outside in below freezing weather. You then ran another tub of hot water, and did the experiment between those two. It definitely seems impossible to me that the new hot one would freeze first, which leads me to believe there must be something measurably different between the cool tap water version and the cooled down hot water.
Here’s an example [0].
1. Warm liquid changing the nature of the freezer (Derek mentions melting frost into a conducting layer but there's also warm water triggering the thermostat of a freezer to work harder)
2. Supercooling can prevent ice forming in calm water, even when the water is below freezing (the effect is wildly unpredictable leading to experimental problems)
Derek then quotes the following study and meta analysis from 2016 that carefully accounts for these and other problems, which finds no evidence of the effect and concludes the other studies' claimed effects are within their own margins of error (including issues like placing thermometers at slightly different locations in a vessel giving dramatically different timing results):
Container 1A - Control temperature
Container 1B - Control temperature
Both go into freezer 1
Container 2A - Control temperature
Container 2B - Near boiling
Both go into freezer 2
Now see if there's a difference in freezing time for Container 1A compared to 2A.
2 glass beakers with same amount of water: 1 hot, 1 cold, stirring both at the same rate. Teacher told us the experiment was over once ice starting forming on the surface…
Cold water developed ice first. Outside in that weather, no one waited to see how long hot takes to become ice.
> Or perhaps external factors come into play: A layer of frost in a freezer can act as an insulator, keeping heat from leaking out of a cold cup, whereas a hot cup will melt the frost and cool faster.
Evaporating water takes quite a lot of energy so the rest of the water is cooled:
> During evaporation, energetic molecules leave the liquid phase, which lowers the average energy of the remaining liquid molecules. The remaining liquid molecules can then absorb energy from their surroundings. This process can take place at any temperature because some of the molecules in a liquid will always have enough energy to enter the gas phase.
Source for the quote: https://highschoolenergy.acs.org/content/hsef/en/how-can-ene...
I always thought this was the reason when observing the effect when trying to pour hot instead of cold water to defrost your windscreen during cold winter months :)
This sounds like a risky experiment, the windshield is likely to shatter with such thermal differences and the associated tensions.
If I am not mistaken, a windshield is created already with internal pressure to ensure it will shatter to pieces when the local pressure changes abruptly (via punching e windshield with a hard pointy object for instance)
Quite counter intuitive. You would expect to have water cooling slow down when it reaches temperature of colder water.
I got a little hyper focused and spent well into the night scrawling equations on a huge whiteboard and I don’t think I ever felt that I proved it one way or the other.
I remember being pretty defeated because I thought I had all the knowledge I needed to solve the problem. I guess it wasn’t so simple after all :)
Is there something I'm missing?
The coffee cools faster if it's hot. So putting in the creamer immediately steals the most efficient cooling period for the coffee. There are some caveats that I don't consider that could make a difference like that the surface area of the combined liquid is larger so it transfers heat more efficiently.
I don't know enough to argue with any confidence but this is very surprising to me. Ignoring for a moment the thermal conductivity of different mug materials, it seems like a large amount of energy would go toward heating the mug up to near liquid temperature rather quickly. Then you'd have at least as much heat loss between the mug and air (compared to exposed liquid and air).
The mug I imagine we're talking about is a ceramic mug, which I believe to have high thermal conductivity just based on what processor covers are made of. It also has plenty of mass.
If you're talking about an insulated mug obviously this changes. But just the fact that insulated mugs exist proves my point that a large amount of heat is lost through the mug...
However, if we really want to overcomplicate things we could consider the possibility of an insulating air pocket in a half-empty cup, leading to less convective losses. Consider a vacuum flask half full of hot coffee outside in a strong wind. If you fill it to the brim with creamer it might cool faster. Evaporation might become important too.
Correct, and we're trying to optimize for hot coffee after 30 minutes. We want cooling to be less efficient.
If you remove those units at the start, you've reduced the starting temp a bit, but you haven't much changed the long tail of the cooling. You essentially just started the coffee at a slightly cooler temperature, but this doesn't affect the curve much. Or to think of it another way, the change in temperature at the start corresponds to a small amount of X axis (time) on the curve.
If you add the cream later, the temperature reduction corresponds to a larger amount of time on the curve. This means the temperature will be lower than the above.
So to my intuition, cream first should yield hotter coffee
You had all the knowledge needed to solve the problem, you just chose the wrong approach :)
The article goes into the difficulties in analysing out-of-equilibrium systems (both experimentally and theoretically).
Btw, I have seen similar experiments in really cold climates, where a cup of hot water thrown freezes immediately, but cold water does not.
Anyways, I am always one for running the experiments :)
IIRC this is because the surface tension of hot water is significantly lower, so the thrown hot water disintegrates into much smaller droplets, which freeze more quickly.
I have no idea if this is accurate.
I would not use this plumber.
[1]: [Czech language] https://www.moni.cz/aktuality/tepla-voda-jako-pitna
Find an old tank and open it, and you'll never even consider drinking that water.
See also Tom Scott's video on Britain's history with separate hot and cold taps and why hot taps sometimes had unsanitary cold water tanks to supply them: https://www.youtube.com/watch?v=HfHgUu_8KgA
For Geneva: you can drink the hot water
For France: you can drink the hot water but it is disgusting
All of them talk about the same effects (fisdolved oxygen, piping ,...) and come to different conclusions.
My take on that: nobody questions the potability of cold tap water so I will use that one, there is nothing to gain (possibly a shorter time to boil? that trumps the extra cost?)
if hot water takes shortcuts and freezes faster than cold, then it requires less energy to do so - that is the crux of the debate
You say that as if entropy ain't realy.
> if hot water takes shortcuts and freezes faster than cold, then it requires less energy to do so - that is the crux of the debate
You can't escape the first and second laws of thermodynamics.
lol no. Those pipes never even got warm. Ice makers don't use anywhere near enough water to flush even a short line.
---
For doing the math! Many ice makers use about four fluid ounces of water per cycle, slightly over 100ml: https://products.geappliances.com/appliance/gea-support-sear...
Per hourly cycle. Or nearly.
When was the last time you turned on the hot water an hour after anyone else used it, and had even the most sightly warmed water within one half to one third of a glass of water?
Never. Even the under-sink heaters hardly work that fast, and their water only has to travel like a meter at most.
This means, once the hot water within the pipe has cooled (within the pipe) it'll still have the same gas content as cold water.
dT/dt = kT
Where T is temperature delta, t is time, and k is some proportionality constant. So the rate of cooling is changing as the delta temperature reduces, specifically, it is getting exponentially reducing as it gets closer to thermodynamic equilibrium (where no heat is exchanged):
T(t) = Ce^kt C = T(0)
Which means there is a larger cool down with the hot water at first, but under this simple model, once the T(t) hits the same temperature of the cool water it's being compared to, it's cooling rate should be equivalent (and a lot slower).
This all just feels like sloppy measurement of some kind.
It could be better written as: exposing hot water to a large temperature gradient allows the water to change energy states in a way that it cannot do when that temperature gradient is small. Those fun new energy state changes allow the hot water to give up more energy faster and freeze sooner.
So no, the hot water in this case is not becoming cold water in the sense that you mean.
I have an undergrad degree in physics and nothing you just said sounds right at all. It all just sounds like gibberish. What kind of "energy states"? Molecules bounce off each other and vibrate around. The measurement of that kinetic energy is called "temperature".
> The abstract findings suggested that the components of a hotter system, by virtue of having more energy, are able to explore more possible configurations and therefore discover states that act as a sort of bypass, allowing the hot system to overtake a cool one as both dropped toward a colder final state.
> “We all have this naive picture that says temperature should change monotonically,” said Raz. “You start at a high temperature, then a medium temperature, and go to a low temperature.” But for something driven out of equilibrium, “it’s not really true to say that the system has a temperature,” and “since that’s the case you can have strange shortcuts.”
Maybe the hot water is somehow more able to align its molecules in a crystal structure faster, and this somehow causes it to freeze first?
2 glass beakers with same amount of water: 1 hot, 1 cold, stirring both at the same rate. Teacher told us the experiment was over once ice starting forming on the surface…
Cold water developed ice first.
https://www.pnas.org/doi/10.1073/pnas.2118484119
A cold system normally takes longer to warm up than a cool system. Yet recent theoretical studies have suggested that the reverse may sometimes be possible. Here, using a colloidal particle in a heat bath, we present experimental evidence for this inverse Mpemba effect. By carefully choosing the energy landscape, we can make the cold system heat up exponentially faster than the heating rate of cool systems. While similar behavior has been seen in systems that cool down—the Mpemba effect—we find that entropic effects generally make anomalous heating harder to observe than anomalous cooling.
For this reason, switching off the gravity stops the convection.
1. The larger the temperature differential, the faster the heat transfer.
2. The outer layer of hotter water will lose temperature very quickly and generate a convection flow inside the container, which would replace outer layers of now colder water with hot water relatively quickly, accelerating the heat transfer.
3. The outer layer of the colder water will lose temperature much more slowly, thus the convection will be less pronounced, not significantly accelerating an already slow heat transfer.
Of course all this will depend, non linearly, on:
1. The temperatures involved (1C water will certainly freeze faster than 99C water when put in a -25C freezer).
2. Shape of the containers (as it affects the convective flows and hence the heat transfer).
3. Total mass of water: I suspect for small (in range of up to decilitres) and large (beyond decalitres), cold water tends to freeze faster. The first, because convection effects are very limited for both waters, and second, because convection effects on cold water become significant enough to improve heat transfer.
4. Environmental conditions: relative humidity of air in the freezer, temperature of the freezer, is freezer empty, are the walls close or far, the actual freezer performance, etc. All of that affects the heat transfer coefficient and make it potentially non constant and not equal between the two waters.
My daughter tried to replicate the effect in our home freezer for a science fair project. Apparently her experimental parameters were not tuned just right because she was not able to replicate the effect. The fair judges were very interested in her project, even though she wasn’t able to make it work.
When I was a kid I used to keep lizards as pets. I quickly noticed that if I filled up the water trays with cold water it would evaporate within a day from the hot heat lamps. Hot or very warm warm out of a kettle would last much much longer. I made a study as a science experiment for school and scored badly as the teacher said it was impossible.
"Mpemba opted to skip waiting for his boiled-milk-and-sugar concoction to cool to room temperature like the other students had done. An hour and a half later, his mixture had frozen into ice cream, whereas those of his more patient classmates remained a thick liquid slurry..."
Boiled milk and sugar is not going to freeze in the same way as pure water, there are effects from the mixing of anything, but some of the substances in milk are oily so you might even have colloidal effects. It seems like if that's where Mpemba first saw it, you should start there to attempt to reproduce it?
So given a big enough surface (turn it into a foam) should allow it to dissipate the heat much faster, then a liquid, were the energy first has to do a slightly chaotic thermodynamic walk to the surface (away from gravity), aggregate with other local energy spikes into one spike big enough to eject a molecule from the bonds and allow energy to escape.
Sending soundwaves through the liquid that intersect with each other creating cavitys, aka foam would also help.
Just encase someone wants to know, this can be measured in BTUs British thermal units. It's the measure of energy used per heating water till it's boiling point . It's also measurable if cooling the water to it's freezing point.
Fun fact is about state changing from 212 to 212 liquid to vapor is significantly more BTUs then the 1:1 (btu to one degree Fahrenheit) .
- hot tap water has more mineral contents than cold water which helps form the initial ice crystals
- hot water in a container creates a convection effect on the air surrounding it, thus creating an influx of cold air around the container, helping cool more quickly
- hot water in a container melts the ice/snow under it (if the experiment is conducted outside), reducing the insulation with potential colder ground
- thermal motion of hotter H2O molecules may help create accidental collisions that trigger the formation of ice crystals
I still don't know what happens if I put two glasses of water, one at room temperature and the other at 100 C, into a freezer and determine which one freezes first. If I don't see the hot water freezing first all (most?) of the time, there's nothing else to consider.
Maybe the controversy has to do with the lack of solid experimental data.
The effect must be very small for it to be so difficult to measure.
Key point there, at the very end, worth taking on board (which is different from listening to every willfully ignorant nutter).
You can't account for all confounding variables.
That's what makes them confounding to begin with.
not to mention static vs rolling friction (as in rolling boil)
So it quickly reduces temperature.
Maybe a more thermodynamic way to state this is:
- temperature is an aggregate measure, so because of the nature of the ensemble, you can have some states at -22 C that still have some molecules of water (or groups of molecules of water connected by intermolecular bonds), at a higher temperature.
- when you start higher, you are going to end up with more of these higher temperature pockets in your ensemble, as your aggregate temperature drops through the degrees toward freezing
- these higher energy / "higher temperature micro regions", provide more possible microstates for the water crystals to rearrange, than if these intermolecular clumps of water were lower temp, (or were less numerous, as would be the case starting lower), and the higher temp clumps (or pockets, in the honeycomb of partially crystallized water) will probe the space of configurations of molecular arrangements more effectively (than if they were lower temperature, or less numerous, as would be the case starting lower).
- By being able to search more of the configuration space, they naturally are able to more quickly find optimal water crystal arrangements of molecules, where some H20 from the higher temp clumps, can slot into the existing lattice, or accrete onto the existing surfaces of forming ice crystals. So these ice crystals in a solution of liquid that has these higher temp pockets can be more effective at generating the movement necessary to find configurations where molecules, and clumps of molecules effectively fit together in the lattice, letting it find more effective crystal structures, leading to more efficient (and faster) crystallisation.
These other commenters are talking about the same thing:
- https://news.ycombinator.com/item?id=31929552
It's never been controversial. It doesn't.
It's cute a high school kid in Africa did an experiment that had a wrong answer and people are not sure exactly why.
Position in freezer, different sizes etc. And exploring why is worthy of science at all levels.
But this nut jobbery shows why science is broken at a structural level.
It's on them to make this replicable . Which they have not for 60 years
Yet science does not denounce the result after 60 years. Think about that.
There's little point talking about something as broken as "Science" but I suspect this is the same issue as why we have only recently understood syphons. Science doesn't have an answer for when multiple things are happening.
There are multiple genuine things screw up the result. But it's probably mainly one. But since the other things are legitimate science can't converge.