[JP]

By the way, the title of the post, "Will hot water freeze faster than cold waver?" is a bit misleading since it makes it sounds like it always happens.  The question Joe asks in the first post isn't misleading, since he asks if it's possible for it to happen.  Yes, it is possible, but no--it can't always happen.

Will hot water ever freeze faster than cold water.  If it does, why does it freeze faster than cold water?  Thanks for comments.  Joe L. Ogan

JP isn't this his original post?

Where does he say, "if it's possible for it to happen"?

I see that different conditions affect the model! Promoting different results

Phrasing it as "will hot water ever freeze faster..." is asking if its possible that it ever happens.  It is.  The post title "will hot water freeze faster..." suggests a general rule, which isn't the case.  This is a problem where precisely stating the question is important.

[Geezer]

By the way, the title of the post, "Will hot water freeze faster than cold waver?" is a bit misleading since it makes it sounds like it always happens.  The question Joe asks in the first post isn't misleading, since he asks if it's possible for it to happen.  Yes, it is possible, but no--it can't always happen.

Will hot water ever freeze faster than cold water.  If it does, why does it freeze faster than cold water?  Thanks for comments.  Joe L. Ogan

JP isn't this his original post?

Where does he say, "if it's possible for it to happen"?

I see that different conditions affect the model! Promoting different results

Phrasing it as "will hot water ever freeze faster..." is asking if its possible that it ever happens.  It is.  The post title "will hot water freeze faster..." suggests a general rule, which isn't the case.  This is a problem where precisely stating the question is important.

Well, science says "never say never", so nothing can ever be ruled out. However, I've not seen anything that indicates there is even one reproducible experiment that confirms the effect even happens.

[JP]

Ah, but we're not talking about cooling the water. The question was about freezing, but it's not very clear what was meant by that term.

If it means the entire mass of water becomes frozen, the discussion about localized effects may be less important. If it means when the first ice crystal forms then localized effects are more important.

If we are only interested in the rate of thermal energy transfer while the water is still liquid, it's quite simple to include an agitator in the water sample so that it has fairly uniform temperature. In fact, as we (hopefully) agree that pure water only starts to freeze at 0C (at STP), we can then leave out the freezing bit altogether, and focus on the energy that has to be removed to lower the temperature to 0C.

Stirring would probably force the hot cup to always freeze first (neglecting a huge evaporation rate).  I interpreted the question as asking without stirring--just putting two cups of water in the freezer, which is easy to experiment on at home.

I'm reasonably confident that if we run that experiment we will observe that the amount of heat that has to be extracted is always consistent with the initial temperature of the sample.

Whether you stir or not (again neglecting evaporation) the heat removed to freeze the water completely is going to depend (almost) entirely on initial temperature.  (You might be able to make arguments about super cooling, though... which is where stirring might help.)  Since the hot cup has to lose more heat, the entire problem comes down to if it can have a faster heat loss rate throughout so that it can win the race, even though it has further to go.

BTW, if we don't allow the water sample to be mixed/stirred/agitated, how do we even know what its temperature is?

I think you could do it by heating water on a stove top up to a certain (uniform) temperature, then pouring it into the cup.  Temperature is an average kinetic energy, so you could theoretically just take the average over the whole cup once the hot water rises and the cold water sinks (doing that in reality is going to be difficult).  This points out why this isn't just temperature-dependent though, since once the cooling processes begin, its complicated to define a temperature if the water isn't uniform throughout.

There are two interesting points to this "Mpemba effect," assuming its as easy to repeat as the popular science write ups say...  The first is that hotter water can often somehow automatically "boost" its cooling rate when you put it in the freezer.  The second is that it shows how the scientific method works.  If the simple, intuitive model fails, you can either come up with a more complicated and accurate model, or you can do as Geezer suggests and try to account for the complications (by constantly stirring, for example).  

[JP]

Well, science says "never say never", so nothing can ever be ruled out. However, I've not seen anything that indicates there is even one reproducible experiment that confirms the effect even happens.

You can find a bunch of experiments here: http://scholar.google.com.sg/scholar?hl=en&q=Mpemba+effect

Some peer-reviewed papers on the subject:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000063000010000882000001&idtype=cvips&gifs=yes&ref=no

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000074000006000514000001&idtype=cvips&gifs=yes&ref=no

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000077000001000027000001&idtype=cvips&gifs=yes&ref=no

This site also has a bibliography on it: http://www1.lsbu.ac.uk/water/explan.html#mpemba

[tommya300]

"Sublimation, Evaporation, and Condensation
The surface of solid ice or liquid water is a busy place. Water molecules are constantly
leaving it as water vapor and returning to it as ice or water. When molecules
leave the surface, the water is evaporating or the ice is subliming. When molecules
return to the surface, the water vapor is condensing. This simple picture of
water molecules taking off and landing on the surface of ice or water explains
many familiar phenomena. But to complete the picture, we must follow the flow
of energy in this system.
Ice and water both contain thermal energy, which is exchanged between
neighboring molecules and keeps them in motion. While the average water molecule
is unable to break free from the surface, molecules occasionally obtain
enough thermal energy from their neighbors to break their bonds and leave as
water vapor. In doing so, these molecules carry away more than their fair share
of the water or ice’s thermal energy and it becomes colder. Your body uses this
effect to keep cool on hot summer days, when perspiration that evaporates from
your skin draws heat from you and lowers your temperature."

http://www.howeverythingworks.org/supplements/water_steam_and_ice.pdf
------------------------------------------------------
http://www1.lsbu.ac.uk/water/explan.html#mpemba

Initially-cold water freezes at a lower temperature to a more completely solid ice with less included liquid water; the lower temperature causing intensive nucleation and a faster crystal growth rate. If the freezing temperature is kept about -6°C then the initially-hot water is most likely to (apparently) freeze first. If freezing is continued, initially-cold water always completely freezes before initially-hot water.

I see that graph and the temperature decay vs time

Still revising the ideas of the reasons why...from 2006 to 2009, someone will have the final answer applying some new tech measuring tool.

[Geezer]

"A number of scientists have investigated Mpemba's claim, but their results remain inconclusive."

http://physicsworld.com/cws/article/print/24493

This might be one for Snopes. It seems to have become part of scientific (as opposed to urban) mythology. Personally, I blame Aristotle.

Is there at least one repeatable experiment?

[Geezer]

Sorry for the second post, but I didn't think an edit was appropriate.

Let's get back to basics. Before we try to explain a phenomenon, would it not be a good idea to describe what the phenomenon actually is?

I would think that if it is not possible to reproduce a phenomenon consistently, we really don't know what we are investigating. Just because a bunch of people seem to believe that something happens is no reason to believe that something actually does happen.

So, if this is such a well accepted phenomenon, you'd think there would be a well accepted experiment that demonstrates the phenomenon. That being the case, you'd think it would be rather well documented by now.

The Geezer view is that a lot of scientists have had a lot of smoke blown up their kilts. Cold Fusion was debunked because the stakes were so high. I'm not sure this one would have survived an equal amount of scrutiny.

[tommya300]

"A number of scientists have investigated Mpemba's claim, but their results remain inconclusive."

http://physicsworld.com/cws/article/print/24493

This might be one for Snopes. It seems to have become part of scientific (as opposed to urban) mythology. Personally, I blame Aristotle.

Is there at least one repeatable experiment?

Yea Ice melts at 32 degrees F, always

[tommya300]

Sorry for the second post, but I didn't think an edit was appropriate.

Let's get back to basics. Before we try to explain a phenomenon, would it not be a good idea to describe what the phenomenon actually is?

I would think that if it is not possible to reproduce a phenomenon consistently, we really don't know what we are investigating. Just because a bunch of people seem to believe that something happens is no reason to believe that something actually does happen.

So, if this is such a well accepted phenomenon, you'd think there would be a well accepted experiment that demonstrates the phenomenon. That being the case, you'd think it would be rather well documented by now.

The Geezer view is that a lot of scientists have had a lot of smoke blown up their kilts. Cold Fusion was debunked because the stakes were so high. I'm not sure this one would have survived an equal amount of scrutiny.

Yea I was reading weather and evaporations on a large scale and reducing it in scale.
I gain some knowledge here thank you for the patience too.

[JP]

"A number of scientists have investigated Mpemba's claim, but their results remain inconclusive."

http://physicsworld.com/cws/article/print/24493

This might be one for Snopes. It seems to have become part of scientific (as opposed to urban) mythology. Personally, I blame Aristotle.

Is there at least one repeatable experiment?

There are a bunch of experiments summarized in this article: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000074000006000514000001&idtype=cvips&gifs=yes&ref=no

If you can't get to that, the one with the most repeatability seems to be the one by Jearl Walker in the article you cite.   To be fair, "although Walker
reported that he could reproduce most of his results, he still obtained large deviations in some of them."

I'm not sure that comparing this to cold fusion is fair, since cold fusion had/has a lot more funding and it was only claimed once to my knowledge (and then debunked.)  This effect has no where near that level of funding and has claims of observations in several different experiments.   

I strongly suspect this is reproducible, though it certainly doesn't overturn thermodynamics, but that it's not worth the time and effort required to do a systematic study that controls for all the variables.  This one is essentially in the realm of enthusiasts and high school science fair projects rather than high-tech labs.

[Geezer]

I strongly suspect this is reproducible, though it certainly doesn't overturn thermodynamics, but that it's not worth the time and effort required to do a systematic study that controls for all the variables.  This one is essentially in the realm of enthusiasts and high school science fair projects rather than high-tech labs.

I strongly suspect this is a load of complete bollocks  []

This chestnut has been going the rounds for close on fifty years. If there was an actual phenomenon to investigate, I'd think fifty years would be sufficient time for someone to come up with at least one repeatable experiment.

[JP]

The Jearl Walker one seems to be fairly repeatable.

[Geezer]

The Jearl Walker one seems to be fairly repeatable.

fairly?

Don't we need one that is repeatable? Fifty years is almost as old as me.

[JP]

Nope.  So long as you can repeat it at a rate that's above experimental error, it's probably a real effect.  Whether its 50 or 1000 years old doesn't matter if it meets this criteria. 

Understanding all the parameters that effect the result is a totally different story--and one that isn't worth exploring for most scientists because the effort involved in the experiments is far beyond the payoff--the explanation is probably fairly mundane and not very useful (not to mention that any research in this area is probably completely unfunded). 

[peppercorn]

Oh, I see where this is going...
An experiment on water that is dismissed by most scientists...

This is clearly not dismissal, this is subversion by the scientific establishment - as the explanation for this phenomenon would prove the truth about 'cars that run on water' scam invention that big-oil is suppressing  []

[JP]

Mhmm... It's because the water has memory.  But you can only see the truth if you wear your tungsten hat to keep the microwaves out.

[Joe L. Ogan (OP)]

Is it good science to ignore facts?  The anomaly has been repeated numerous times.  If we ignore facts, science will be reflected by who can shout the loudest.  I do not believe that science should be based on who can shout the loudest.  Thanks for comments.  Joe L. Ogan

[lightarrow]

maybe this is possible Geezer?

Producing a miniature weather pattern:
Steamy energetic water, in  a container, producing water vapors, is placed in a freezer.
The surface of the water in the container is cooling as the vapors escape.
But not all water vapors are lost, some condense and circulate above in a cycle to attempt to gain a lattice crystal structure, precipitates, dropping to the surface and transfers the exchange of heat.
When the water surface reaches its highest density the lattice crystallization begins at the condensed vapor level  and begins to displace the warm water below it. As this happens water begins to freeze at the surface first.
It is the vapors of the hot water creating an additional heat sink.
Note it is slushy not solid ice.
The other room temperature water does not have the abundance of energetic water vapors to do this extra heat sink exchange. 

So the effect would be given by gravity and differences in densities of water, not on the fact it's hot or cold. You couldn't generate such effect in the absence of gravity/ you could generate it in the absence of temperature differencies.

[Joe L. Ogan (OP)]

So, maybe I am wrong.  Perhaps science is and should be based on what those think that can shout louder and longer than others.  Thanks for comments.  Joe L. Ogan

[tommya300]

maybe this is possible Geezer?

Producing a miniature weather pattern:
Steamy energetic water, in  a container, producing water vapors, is placed in a freezer.
The surface of the water in the container is cooling as the vapors escape.
But not all water vapors are lost, some condense and circulate above in a cycle to attempt to gain a lattice crystal structure, precipitates, dropping to the surface and transfers the exchange of heat.
When the water surface reaches its highest density the lattice crystallization begins at the condensed vapor level  and begins to displace the warm water below it. As this happens water begins to freeze at the surface first.
It is the vapors of the hot water creating an additional heat sink.
Note it is slushy not solid ice.
The other room temperature water does not have the abundance of energetic water vapors to do this extra heat sink exchange. 

So the effect would be given by gravity and differences in densities of water, not on the fact it's hot or cold. You couldn't generate such effect in the absence of gravity/ you could generate it in the absence of temperature differencies.

Another condition added to the model?
Redefine the question to fit your statement may help?
Why does water freeze from the surface down?