Cash prize offered for solving Mpemba effect

RonL

It seems quite simple in my mind,

The hot water has a more aggressive internal action, which will reflect a greater distribution of heat as it declines in temperature. The distribution of heat at a faster rate will reflect less heat overall throughout the liquid, this means a cooler central area.

When the two volumes are at an equal temperature, the hot has dispersed more heat as it declined and still has a greater internal kinetic action taking place, this continues to more evenly move heat to the boundary layer points of heat transfer, thus that center volume has a lower temperature and becomes solid before the cold container.

This is my thought process and no prior thinking, other than hearing the statement and had always discounted it's validity, the thread put my mind to work.

DragonPetter

Assuming that this is a real effect, then is it only valid for water? If so, then the explanation can only apply to water.

Andre

Deadline today. I just did submit something and I wonder if own thoughts about the results of my little experiment can be posted here.

sophiecentaur

What puzzles me is: the temperature of the 'hot water' will drop. On the way, it will pass the temperature that the 'cold water' started at. Unless there is some other factor that the experimenters haven't told us about, it is then the same stuff at the same temperature that the cold water was (it is now 'cold water') but later. How can it then (from that temperature) cool faster and overtake than the other lot of water?
Although I can't say that the effect could never happen under any circumstances, this is just not a fair test, as described - because it isn't actually described.
Possible factors are: dissolved gas affecting the latent heat of fusion, convection currents in the hot water allowing faster heat transfer by stopping the formation of an insulating of ice on the outside of the initially cold water, the thermostat (my favourite).

I heard this statement as long ago as 1954 (ish), when we (the family) bought our first Fridge. But at nine years of age, I didn't question it too much - just enjoyed ice lollies at home for the first time. (popsicles - for our trans-atlantic cousins)

ZapperZ

Just in case people are not aware, there has been quite a number of studies, both experimental and theoretical, on this effect:

http://arxiv.org/abs/0704.1381
http://arxiv.org/abs/physics/0604224
http://arxiv.org/abs/physics/0512262
http://arxiv.org/abs/1003.3185
http://arxiv.org/abs/1101.2684

Zz.

sophiecentaur

But, from what I read of those abstracts, the conditions aren't all defined in the same way. They are quite specific and sophisticated. It makes me wonder what the original statement (not the OP - I mean the really original one) was really about.

I don't think it ever meant that when you put your ice cube tray in the freezer, it's better to fill it with warm water. THAT is what everyone immediately thinks it's all about.

Andre

Meanwhile I did some interesting observations.

As I was alerted yesterday on the the contest, I did some hasty unsophisticated tests.

The hypothesis about impurities like dissolved gasses, delaying crystal forming appeared reasonable. So I used three small sealed containers with precooled boiled water and just tap water and one with hot tapwater. At around 50 minutes in the freezer, the cold boiled superfroze upon touching. Eventually the tap water followed. The warm boiled came last. That seemed to confirm that idea.

Today I wanted to reproduce that and to see if the hardiness, would also affect it, I also used rain water. We have a lot of that. I used small glass (test) tubes and sealed off the water with olive oil to prevent evaporation cooling and re-aeration

At a certain moment at which I expected some freezing, all appeared still liquid. So I touched the water surfaces with a toothpick.
When I touched the set, the control tube flash froze. When I touched the precooled boiled samples, nothing happened, still liquid. But upon touching both initial hot samples flash froze.

Back to square one, or does anybody have an idea?

( I do )

Apart from that it struck me that the flash frozen crystals sank rather than floating.

Andre

This picture was taken right before the touching test

#1 and #2 are precooled boiled tap and rain water |(that did not react upon touching)
#3 is plain, not precooled tap water (apparantly already partly frozen)
#4 and #5 are initially hot boiled tap and rain water (that flash froze upon touching a few seconds later).

Something trivial :P struck me there.

krd

Think of it in terms of two buckets - a warm bucket and a hot one - most of the heat is lost at the top of the bucket. In the warm bucket there's a warm trapped layer in the middle of the bucket - it's trapped by falling cold water. In the hot bucket the middle layer is more energetic, and breaks through to the top of the bucket where it cools quicker. The hot bucket even pushes down cold water with more force. The distribution of heat in the two buckets is completely different.

IF.......You had an stirrer going in both buckets......the cooler bucket would freeze first.


I heard about this competition a while back. I think they were looking for a fancy pants demonstration. Doing it with thermal cameras and a walk in freezer might be a thing - then quite a bit of experimentation to get the optimal temperatures for the demonstration. It will probably be done by some precious rich kid nerd (with lots of help) who will then go on TED Talks, and make us all want to vomit.

Andre

I wanted to make clearer pictures so I wiped the condensated water off the tubes and then...?

krd

I think your tubes may be too small.

And before doing these, or any other, experiments, you're meant to have some kind of theory.

krd

But there should be less dissolved gasses in the hot sample than the cool one.

For crystal nucleation total absence of impurities is more of a problem. Once the crystals nucleate they get going. Beyond a certain point it doesn't really matter how much impurity is in the water.

The Mpemba effect is a conversation piece. It would be a real pain in the *** to actually replicate. Though I think I may have seen it as a child. I think it may be important in the way jelly/jello sets in the fridge.

DragonPetter

So they drill in your head in high school science class on the scientific method. I don't think he is planning to submit his observations to any peer reviewed journal. Also, hypothesis != theory, even though that's not even necessary. It can be a helpful tool to guide your experiments, and if you want to prove something, you need one, but there's no scientific rule that says you need to have one to simply make observations. Even experimenting, by itself, is not the scientific method. You don't need to have a theory to make controlled observations. Many theories came after observations.

Do you think Maxwell's equations existed before Faraday?

krd

No, but he's trying to repeat an effect that has already been observed.

The whole Mpemba combination - and I think they have prizes for a whole bunch of similar problems. It's not just that should be able to repeat it, but you also need a theory to make it repeatable.

I think it might take quite a deal of messing around to find the ideal conditions.

Once an effect has been observed - then you need a theory - if the theory allows a reproducible result, then maybe you have something. But it has been reproduced. If I was going to do it, I'd try to track down any of the notes or people who'd been involved. Set up the conditions to repeat it. Look into the body of knowledge that might cover it - set up my thermal cameras and buckets in a walk in freezer.

Andre

Sorry if I confused you, we completely agree there. The idea is that hotter water freezes quicker because of that effect.

But with confusions like these you may wonder what causes you to be on the wrong foot.

Oh and I submitted those observations I did in he second test, I'm just wondering if anybody sees what I see, with the key word 'condensation'

krd

I don't think you're onto anything there. The condensation will be thermally neutral, and if anything may act as an insulator.

Your cool tubes, were cool enough to allow condensation, and not hot enough to stop it.

You know when you get wet, you feel cold?....That's because the thin layer of warm air is no longer over your skin. So, your body cools quicker. But that principle is not a factor in the Mpemba effect.

I think one of your problems in the reproduction of the Mpemba effect is your tubes are too small - too much surface area in relation to your volume.

russ_watters

I did a test a few years ago with coffee cups. Results still negative.