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Old 06-27-2012, 02:27 PM   #1
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Can SMP Solve the Mpemba Effect mystery?

Royal Society of Chemistry offers $1600 prize

Quote:
Why does hot water freeze faster than cold water?It seems a simple enough question - yet it has baffled the best brains for at least 2,300 years.

•Aristotle agonized over it fruitlessly in the fourth century BC
•Roger Bacon in the 13th century used it to advocate the scientific method in his book Opus Majus
•Another Bacon, Francis, wrote in his 1620 Novum Organum, that "slightly tepid water freezes more easily than that which is utterly cold" but could not explain why
•Descartes was defeated by it in the 17th century AD
•Even perplexed 20th and 21st century scientists and intellectuals have swarmed over it without result

Now the Royal Society of Chemistry is offering £1000 to the person or team producing the best and most creative explanation of the phenomenon, known today as The Mpemba Effect.
A guy once tried to tell me that cold water boils faster than hot water. I told him he was talking nonsense. As far as I know he was. But now I see something similiar which I've never heard of before. Tepid water freezes faster than ice cold water?

It would be cool if SMP could submit a winning solution to this mystery and make 2+2 famous in Royal Society circles.


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Old 06-27-2012, 03:09 PM   #2
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Re: Can SMP Solve the Mpemba Effect mystery?

Water does seriously weird **** at surfaces. If I had to hazard a guess, I'd say that low-temperature water forms an insulating layer around the surfaces of the vessel (and the top of the liquid to a lesser degree) that higher-temperature water doesn't form allowing for better heat transfer to the environment, and as high-temperature water cools, it doesn't cool uniformly, and the thermal gradients keep enough convection going to prevent that layer from forming quickly in the formerly-hot water. I would be quite surprised if you took identical water (except for T obv) in identical vessels, both with good magnetic stirring, and the cold water didn't get "fairly frozen" faster.
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Old 06-27-2012, 03:17 PM   #3
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Re: Can SMP Solve the Mpemba Effect mystery?

I remember being told it was because there is less gas dissolved in warm water. Since it was the only explanation I've heard I assumed it must be the reason, but I guess it's not.
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Old 06-27-2012, 03:57 PM   #4
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Re: Can SMP Solve the Mpemba Effect mystery?

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Originally Posted by TomCowley View Post
I would be quite surprised if you took identical water (except for T obv) in identical vessels, both with good magnetic stirring, and the cold water didn't get "fairly frozen" faster.
That would be a pretty good way to test your theory. I'm actually pretty surprised the solution hasn't been discovered yet. You'd think industry would need to know this sort of thing and some engineer would have figured it out by now. It's hard to believe £1000 is going to do the trick.
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Old 06-27-2012, 04:33 PM   #5
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Re: Can SMP Solve the Mpemba Effect mystery?

Somebody could test this at home with 2 glasses and a vibrator. (See if effect exists in the glasses alone. If so, see if effect still exists if a running vibrator is sitting on top of them)
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Old 06-27-2012, 05:09 PM   #6
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Re: Can SMP Solve the Mpemba Effect mystery?

Can you see the Mpemba Effect in other liquids too?
Not only the faster freezing but also going faster from T1 to T2.
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Old 06-27-2012, 05:48 PM   #7
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Re: Can SMP Solve the Mpemba Effect mystery?

You cant seriously try to answer this without complex physics that deals with the phase transition mechanism and how it takes place across the body of water depending on the environment and the condition of the water that in principle is different from boiled and cold. The container geometry also may play a role. Also the exact content of water matters (is it 100% water molecules, eg real drinking water never is that plus it has minerals/salts etc).

I am also willing to claim the answer depends on how fast the system is forced to freeze.

I sure hope its not a hoax as i have no personal experimental familiarity with such effect so i take it now for granted by the references. It should be a physics no chemistry problem though unless its a physical chemistry subject that chemists are more advanced in dealing than many-body/liquid state/phase transition physicists. But real material scientists are the only ones that can do it right (ie physicists) if forced to do the real problem in all its glory.


Another thing to ask is if the ice formed is identical in structure in both waters.



Something i have observed however that is different but maybe similar in explanation ultimately is that water that has been boiled and then cooled and forced to be reboiled again arrives at the rapid bubble phase without the gradual bubble phase that the originally cold water had (just get water from faucet and boil it and observe how it arrives to rapid bubbling gradually, then coolit and repeat boiling, there is always an earlier gradual slower bubbling phase before the intense one sets in in the fresh water. Of course that could be a result of the air diluted in the water having been mostly released from the original boiling.


The very first experiment i would do is take water that has been thoroughly boiled many times to remove any air and then start the experiment with this type of totally clean 100% , air free water from same cold temperature always of course and then boil and try to freeze etc . Then report and only if then we still have a difference the problem is real interesting.

Also i am ultra confident the starting temperature of both waters matters and seriously you cant expect that water that is real cold vs 90 C degree water will still lead to 90 freezing faster. The hot water seriously takes time to become cold before freezing is possible. To bypass that extra time would be ridiculous unless they both start the attempt to freeze from close enough temperatures or the coldest one is not very close to 0 anyway.


Edit: Read some of what i said (concerns for set up) and other here http://en.wikipedia.org/wiki/Mpemba_effect

Last edited by masque de Z; 06-27-2012 at 05:59 PM.
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Old 06-27-2012, 06:04 PM   #8
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Re: Can SMP Solve the Mpemba Effect mystery?

Other simple thing to study is to try to start cooling down hot water and see how fast the 100C goes to say 5 C vs how fast the slightly warm 35C goes to 5 C using identical coolers. Is it a race between 100and 35 or 100 and 10 or is it a more proper race of 100 down to 20 (that period not counting) and 20 waiting for the 100 to reach 20 and then both introduced in a freezer. That last thing would be intriguing for sure if they both started from same temperature when entered in the cooler. Especially if they had similar air content,salts etc

What must be established is how intense the effect is as function of the water contents and how it changes as the starting 2 waters temperature difference changes and also how it changes if the cold water is far from 0. Also how it changes as the cooler becomes slower or very rapid in cooling ability.

Basically its all garbage without proper set up and study of what affects the phenomenon.
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Old 06-27-2012, 06:11 PM   #9
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Re: Can SMP Solve the Mpemba Effect mystery?

Supposedly it has been observed in boiled and DI water. Supposedly it's also observable, at least for some starting setups, even as faster arrival at a certain temperature (although as you point out, obviously this isn't going to hold in all setups) before anything actually freezes, so there's something going on that isn't related to phase changes (assuming all of that is true). If so, it really doesn't leave much.
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Old 06-27-2012, 06:11 PM   #10
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
Originally Posted by masque de Z View Post
Other simple thing to study is to try to start cooling down hot water and see how fast the 100C goes to say 5 C vs how fast the slightly warm 35C goes to 5 C using identical coolers. Is it a race between 100and 35 or 100 and 10 or is it a more proper race of 100 down to 20 (that period not counting) and 20 waiting for the 100 to reach 20 and then both introduced in a freezer. That last thing would be intriguing for sure if they both started from same temperature when entered in the cooler. Especially if they had similar air content,salts etc

What must be established is how intense the effect is as function of the water contents and how it changes as the starting 2 waters temperature difference changes and also how it changes if the cold water is far from 0. Also how it changes as the cooler becomes slower or very rapid in cooling ability.

Basically its all garbage without proper set up and study of what affects the phenomenon.
Agreed.
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Old 06-27-2012, 06:27 PM   #11
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Re: Can SMP Solve the Mpemba Effect mystery?

Another thing related to boiling is that most of us i think have observed when you boil water you see the first small bubbles originate from the bottom of the vessel. Clearly when you try to boil in the warming up phase the temperature of the water is not the same across all its volume. The layers of water close to the metal surface obviously get heated high first and probably have a higher temperature during the process until all of it has reached 100 or nearby. In a cooling process similar effects on the reverse take place as the core of the water is obviously surrounded by other external layers (plus of course you also have some transport) that are the first to lose energy to the environment of the cooler on the race down.
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Old 06-27-2012, 06:39 PM   #12
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Re: Can SMP Solve the Mpemba Effect mystery?

Water, when it freezes expands, contrary to others which upon freezing contract. In effect, since the water (ice) is in an expansive state the amount of warmth needed to bring to boiling point is less than if the initial state is liquid water. Conversely, going in the opposite direction can be related to this originality of quality in water.

The expansion of water at the freezing point is a great anomaly to consideration of any type of mechanistic approach. If water didn't expand how will we have ice hockey? It's a real troubling point especially if you're a Montreal fan who can use some expansiveness to their personalities( in joke to hockey fans which probably doesn't make any sense in any case).

It would be interesting to document the quantity of evaporation of ice and liquid water in various states. I really haven't got this bull's eyed yet but the fact that water is unlike any other material in the earthly realm at or around its freezing point is significant.
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Old 06-27-2012, 10:02 PM   #13
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Re: Can SMP Solve the Mpemba Effect mystery?

Mpemba Effect
Quote:
If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first
So evidently, as the 100C water cools down to 35C its condition when it reaches 35C must be different than the initial condition of the water that started at 35C. What would the difference be?


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Old 06-27-2012, 10:34 PM   #14
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Re: Can SMP Solve the Mpemba Effect mystery?

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Originally Posted by PairTheBoard View Post
Mpemba Effect


So evidently, as the 100C water cools down to 35C its condition when it reaches 35C must be different than the initial condition of the water that started at 35C. What would the difference be?


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If the vessel is has non-negligible thickness, then the difference is probably a larger temperature gradient within the vessel.

I would like to see this experiment done with a sealed "thin slab" of water (this removes evaporation as a factor as well as the temperature gradient). Actually, I suspect someone has already done it. But I just don't care enough to look for it.
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Old 06-27-2012, 11:56 PM   #15
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Re: Can SMP Solve the Mpemba Effect mystery?

I'm not completely convinced this actually happens and is a robust effect...but maybe something with nucleation site density?? Though I have no idea why it would be higher for water that was recently hot.
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