Freezing Hot Water vs Cool Water

Is it similar to dust(flower, grain dust) fires? because the oxygen can access the dust more easily. I think hot water molecules that vibrate leave room for the cold to get in, while cold water is more tightly packed. I am out of my league here, i am just guessing

Heat is vibration, so how does that work in with your theory?

Cold is lack of hot ! There is no cold and hot different energies.

The flow of temperature is only a one way street. hot to cold

Thank you for the valuable additional information.

or is it hot to less hot? the word cold is only adjective.

Instead of adjective, maybe a better choice of words would be relative

probably meant "subjective"

I'll defer to the experts that will respond with specifics, but it goes something like this.

To freeze a unit volume of water at 1 degree C takes the relevant energy for the phase transistion to solid for that volume.

To freeze the same volume of HOT water takes the energy required to get it to zero, but when it gets to zero there is actually less volume (co-efficient of thermal expansion stuff) and then the energy to freeze that reduced volume.

The reduced volume of the hot water means that there is less total energy to remove to take it to solid.

This is false. It takes longer for warm water to freeze than it does cold water.

I have tried it.

Aristotle aside, the experiments I ran proved otherwise.

I guess if one were in a hurry to freeze water, they could boil it first, just to hurry things along.

Don't boil it in a microwave...

great,,,, now your going to get the thread closed down.

So, if your experiments proved otherwise, does that mean you believe that all other experiments that disagree with your results are also invalid?

Yes! If I think of any others, I'll let you know what they are.

Alright, I'll take a GA away. ............... ^{u big pussy u}

The explanations here and other places I've made a quick check seem to be lacking a critical detail...that being time held at the initial 'hot' and 'cold' temperature for the two different samples.

There must be some non negligible hold time required at the starting temperatures. If there weren't, then a new container of water at the 'hot' temperature could be placed in the freezer as soon as the original 'hot' container had reached the original 'cold' temperature, and the new container should freeze more quickly than either of the originals. Repeat a couple of times and you could reach impossible temperature change rates.....suggesting that something is missing in the explanation.

So, do you know what the requirement is for the history of the water prior to the 'start' of the experiment?

Nobody has addressed the CONTAINER. the water has to be contained in something and that is going to affect the experiment. Would certainly explain why one fellow would get the expected result (cold freezing faster).

Actually, you are correct. I used aluminum containers, ignorant of the fact that to make the miracle work, one would need to use an insulating "beaker".

Perhaps the secret is glass. It was around long before aluminum.

The rate of heat transfer is proportional to the difference in temperature. The hot water is going to cool much faster because the temperature differential is greater. The ability of water to stratify may be playing a role here. Molecules have what are called "crystalline structure," it refers to how they orient to each other. I am wondering if perhaps if the hot water is placed in a sufficiently cold freezer with a low-density container, like a paper or plastic cup (so as not to interfere with the experiment) if the lattice structure of the hot water holds it's structure or skips a change. liquid water is at its most dense at 39 degrees, which is kind of counter-intuitive. The answer re: reduced mass of hot water versus cold water (of equal volumes) coupled with the rate of heat transfer might alone explain it without taking into account changes in crystal lattice structure. Maybe the warm water stratifies while the hot doesn't and this somehow affects the experiment? The hot water would be sufficiently "degassed" compared to the cold. Cold water holds more co2 and oxygen than hot water. Maybe this degassed state plays a role by speeding the heat transfer throughout the water molecules more rapidly.

Thats the other thing, earlier that freezing water from a hot water heater is because there is a lack of gases in there is a lack of bubbles so it would freeze faster.

for nucleation to occur, there has to be something for the crystal to latch onto to form, such as........ dust particle, bubble and so on.

What happens is that it nucleation forms on the sides of the container side wall if the water is degassed and .....pure. Which now leads us to purity........then we have to talk about .......ionized water or de-ionize? of which can be quite....corrosive.

Earlier, I always thought thermals was boring..........when in fact its quite......interesting, after I actually needed to know some fundamentals for actual applications

So what is your point here?

Obviously, you are not trying to debunk the science, right?

Obviously... I'm not trying to debunk the science.

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I CAN'T. NO ONE CAN.

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Experiment methodology devoid of rigor made that a certainty.

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No true rigor = no true science.

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No science = nothing to debunk.

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obviously, I'm not trying to tell you I find the conclusions of Aristotle and Mpembe irrefutable, just unreliable.

I have not tracked down experiments, but it seemed a fair assumption that the effect was real given that there is a reward for the solution to the problem and the number of years that it has been known (both since Aristotle and Mpemba's work).

Might have been better if the reward were for doing a rigorous, peer-reviewed experiment to confirm the effect is (or is not) real.

Sounds to me like the sort of thing a lot of people would like to believe is true, as it has a nice paradoxical ring to it.

Have you taken any time to research this or is this a case where you have already made up your mind and no further discussion (or facts) are necessary?

You can do a quick search on the net for the Mpemba Effect and find qualified experiments like this one.

If you are still unconvinced, run the experiment yourself.

Given the overwhelming evidence that demonstrates this effect it seems senseless to argue the point, but feel free to prove or disprove this for yourself.

AH,

The link is broken.

I find it difficult to conceed that terms such as "slightly warm" and "tepid" when related to an experiment could be construed as "science" by anybody.

The imposition of so many preconditions to achieve success with the experiment leaves me cold. Pun intendeed.

I will conceed that, under certain controlled conditions, warm water may freeze more rapidly than cooler water.

This is by no means proof of anything.

I just happen to have some sun handy, and a pyrometer, so maybe during beer n brats tomorrow I'll run some tests.

Happy Holiday!

Sorry, for some reason it won't work.

Try this one and go to the top of the page and hit mpemba effect link to go back to the start of the experiment.

Proof? Doesn't you statement prove that something happens? There is a preponderance of evidence that "under certain conditions" hot water freezes faster than cold water. The whole crux of this post was to explore why.

You have stated that it is true as well, but the question is not if it does or does not exist, it does, but what is the mechanism that drives it?

No I haven't made up my mind in advance, that's why I wrote "....confirm the effect is (or is not) real". I don't mind which way it goes. Do you believe it's already accepted as fact by the scientific community?

The link you posted is interesting but doesn't mention controlling for any of the possible influences discussed in this thread, the one in #11 and in your link about a layer of ice being a likely one in my opinion (if it turns out the effect doesn't exist).

Also the plotted temperature of the flat parts of the curve, 2.5°C is surprising. Expected to be at 0°C, and 2.5° is a big difference.

Yes, I think the effect is real, but I have too many other things in life to do than research and post scholarly links that document the Mpemba effect.

If it were untrue it would seem that the Royal Society of Chemistry would not be wasting time and money offering a prize for solving the puzzle of the Mpemba Effect.

Just how much proof do you need? Are you as skeptical when you are told water freezes at 0°C, or that the speed of light is approximately 299,792,458 m/s, or the existence of virtual particles popping out of an electromagnetic field?

The effect is real. The effect is not real. Therein lies paradox. The environment/parameters of the experiments designed to demonstrate the effect clearly can be manipulated to influence the outcome.

So, no, the Mtemba effect is not novel.

When adequate capacity for heat absorption surrounding the sample, coupled with the increased vapor deposition of the higher temp sample, is combined, the surface of one sample may show ice crystals more quickly than the other. Is this the Mtemba effect? That's certainly where this discussion is leading me, and the challenge issued by the RCoC will never be met.

Demonstrations of one square meter of ice, reaching -1C in the center, in an environment of constant heat removal potential, seem to be more appropriate. I'll post if I find one. It would be fun to see.

GA

Also the plotted temperature of the flat parts of the curve, 2.5°C is surprising. Expected to be at 0°C, and 2.5° is a big difference.

I think you've pointed the way to the flaw in the experiment as performed. They really needed to place temperature sensors at far more than one position in the samples to get a feeling of what was really going on.

'...a fair assumption that the effect was real given that there is a reward for the solution to the problem and the number of years that it has been known...'

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This reasoning is spurious. Neither, the longevity of a commonly held belief, nor the failure to award a prize promised in return for an explanation deemed sufficient, does much to support the idea that the phenomena goes beyond an artifact introduced in either the experimental methodology or the subsequent analysis.

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I'm sure we can agree that there are numerous examples of conflicting beliefs each commonly held over (different) lengthy times, so that can't be a good indicator.

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The failure to award a prize might just as easily be related to the framing of the problem (or the judgement of what constitutes an acceptable answer), as to the existence of some yet unknown property of water.

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Erroneous framing seems to be the biggest problem with the 'Mpemba effect'. The 'Mpemba effect', in making the claim that 'hot water freezes faster than cold water under certain conditions' attributes (without support) the quality specifically to the water and not to the process.

The claim itself is rather unscientific as it requires the reader to fill in some implied but undefined conditions. For example it leaves the reader to make an assumption about the conditions leading to freezing... removal of calories at the same rate, or exposed to the same conditions of contact with a fluid below the freezing point. This is more slippery than at first glance it might suggest.

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The claim singles out water as where the 'effect' occurs, but makes no specific (testable) claims about changes in volumetric or molar heat capacity, heat transfer modes, thermal conductivity, enthalpy of fusion, or freezing point.

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The link you provided to the experiment provides a good example of the some of the problems. The experiments were run for one sample then the other back to back. The description suggests the hot sample was run first. No measurement was recorded of the air temperature in the freezer at the beginning and during the experiment. No measurement was recorded for the amount of time the compressor ran during each experiment. No measurement was recorded measuring the depth of insulating frost lining the freezer at the outset of the experiment.

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Even if the hot sample had not been run first, differences in initial frost thickness, differences in initial freezer temperature, and differences in the percentage of the time the thermostat triggered the internal fans and heat removal by vapor compression system all need to be accounted for.

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I have an analogy... using my toaster at the same high setting, frozen bagels consistently come out black whereas room temperature bagels are golden brown. Do you see a problem if I say that 'frozen bread burns more easily than room temperature bread'?

This whole exercise makes my experiment of 30 years ago seem almost credible.

#3

Okay.

Science? What science?

Et tu, Lyn?

Look at my post Post # 94.

http://cr4.globalspec.com/search/sitesearch?do=show&sort=textmatchrank&srch=zamboni&order=asc

Individual anecdotal observations aside, published reports show that under some conditions, hot water does freeze faster than cold water. This observation even goes back to the days of Aristotle, but surfaced again in the 1960's.

You can read of this in the Wikipedia article: http://en.wikipedia.org/wiki/Mpemba_effect

Does this imply that recently boiled water at room temperature would boil faster than non-recently boiled water at the same temperature?

-A-

According to a physics professor, whom I know to be correct, hot water will only freeze faster if you have a nice layer of frost in the freezer to begin with.

This is because the frost melts more readily with the hot water and thereby improves the thermal transfer to the previously hot water in the ice cube trays.

If you place the cold and hot water on a clean and dry surface that has no contribution to the race, the cold water will always freeze first.

When the air is the only factor for heat transfer, then the cold water has a head start. Calories of heat are like calories of fat. The activity determines the loss rate and sometimes the activity is more than meets the eye!

The water vapor above the liquid water acts as a heat sink and the lower amount of non-condensable gases lowers the insulating effect, furthering the heat transfer speed...The gradual transition in molecular density vs the air to water barrier of the colder water, is the critical difference.....I'll take that in cash...$

Sorry Solar Eagle, I can only write you a check.

Are you telling me that the hot water wouldn't have to face the same air to water barrier that the colder water had to start with? Seems like a leap to me.

Better hold that check for a few days. It isn't good until payday.

Yes, I call it the hazy phase barrier vs the dip your toe in the water(DYTIW) barrier....and I didn't just make that up,,,,maybe

No, it only appears to freeze faster, what actually happens is because it is warmer, the water water actually evaporates more so there is actually less water volume to freeze.

Yes, that was an early proposal, but when you weigh the resulting ice and compare to the initial state they are virtually identical.

Yes the thermal conductivity is not effected, But at the end result, with less mass due to evaporation, your have an ice cube from the initial hotter water as compared to from the initial colder water, Smaller ice cube but an ice cube none the less......

It's a nice theory, but testing showed no significant mass loss, which probably does not account for the entire effect. That would pretty much discount that theory, at least as a sole source.

Yes by itself it doesn't account for the entire effect on was is going with only a small portion that in itself is seemingly irrelevant.

As an analogy, I like to use that its kinda like taxes, Sales tax increase for instance.

This little tax...... Its nothing, its only 0.015% tax. Which can be irrelevent by its self.

Until you add it to:

• the existing 5% sales tax
• plus an addition 1.5% new stadium tax for the new stadium in the area.
• Plus a 1% room tax for tourism,
• Plus an addition tax because your eating in at your resturant instead of take out.
• And anything else tax, that I forgot to mention

And before you know it, your in Liberal Heaven, because you no longer have no take home pay, after you paid all your taxes.

Yes, it's kinda like that, that little bit in itself is nothing, until you add up all the other little nothings, you actually have a very relative effect on you making ice.

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I think that analogy is not relevant.

In order for the water to freeze faster a significant amount of mass must be lost and I think the total loss of mass due to evaporation will be insignificant.

This is not an idle theory. It is simple to mass the water before beginning the cooling process and after the process to determine the mass difference. It would seem unlikely that such an obvious cause would go undetected in experiments.

Ha! You are trying to get this form to tell you the answer so you can collect the $1500.00 prize from UK's Royal Society of Chemistry. You can read about it here. I have a few theories but they need to pass mustard before they ever get accepted. Until then accept the God theory:

"G+YUKS/U=Ice (from) tepid h2O.

Translated for non-geniuses, it computes to, "God having a laugh at our expense leads to warm water freezing faster than cold."

If you find the answer on this form you will have to share the bounty by consensus. I'd settle for a beer.

'...pass mustard...'!!!!

LOL,

Be assured, you are providing a good laugh to many more than just whatever deity floaty thing you imagine.

Thank you.

While your at it pass the biscuits, please. Good catch.

For people making ice sculptures, they boil the water first before freezing it to get clear ice, free of bubbles. I suspect (as others have mentioned) that dissolved gases may be playing a part.

Whoever gave me the "off topic" earlier, Thanks.

I've gone and done some investigations and learnt a lot about water, specific heat and so on. There is truly a paradox in this phenomenon. When I did the sums that my initial guess proposed, the relationship was not feasible. (I was wrong.)

The ratio of thermal expansion compared with the 4.6J/g degree C cooling change does NOT explain this.

That would be a useful experiment, good answer. It would also be worth doing it with 2 samples both of which have been boiled for a while to expel dissolved air (in a clean SS saucepan, not a kettle with a good layer of scale!) left to cool and then one reheated just before putting in the freezer.

And in sealed containers, to obviate the evaporation issue. But then how would you detect onset and completion of freezing? Come to that, how would you do it unequivocally in an open container? Opinion could depend on what you're hoping to prove.

Also interesting to measure temperature vs time of each, which is of course a falling part, followed by a flat part at presumably 0°C, followed by further fall when all frozen. Just maybe it's not exactly 0°C in both cases, due to various effects others have mentioned. Temperature measurement could be a more objective way of defining freezing point.

Another thought - does it depend on the temperature of the freezer? Result for -100°C could differ from that at -5°C.

Another thought - does it depend on the temperature of the freezer? Result for -100°C could differ from that at -5°C.

it would, by created a larger approach temperature differential

Yes, obviously they would both cool quicker. What I meant was would it affect which of the samples froze first?

'....It would also be worth doing it with 2 samples both of which have been boiled for a while to expel dissolved air....'

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The descriptions of the experiment I have read do state boiled water was used in both conditions, attempting to remove variation due to dissolved gasses.

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I think the effect is due to several factors, but the most dominant factors have to do with differences in heat transfer by convection as opposed to conduction....

When both containers are put into the freezer, the freezer air is heated by the warmer container to a temp at of above the colder container. This means that the colder container is only losing heat through the bottom. This initiates a thermal stratification that dampens or eliminates thermal convection currents, since the more dense cold water is already lower than the warmer water.

The warmer container is losing heat to the sides and top (in addition to the bottom). This initiated a current that flows up the center and falls down the outside.

Eventually as the warmer container approaches the temperature of the colder container, the colder container begins to loose heat out the sides and more so out the top....but at this temp close to freezing, water density decreases as temperature falls, which continues the stopping/dampening effect on thermally driven currents.

The previously warmer container still has circulation albeit now slower and continuing to slow. Heat transfer rates are much greater for convection than conduction in most cases, and this is likely the dominant factor....

Unless it really is just that the hot container melts through the insulating frost.....

This raises another question - are both containers placed side-by-side in the same freezer (allowing heat transfer between them) or in separate freezers? If it's 2 domestic freezers the temperatures probably won't be exactly the same, so it would be done twice, with the samples swapped.

What if the hot water kicks in the engine of the freezer which would lead to a quicker freezing while the cold water would not have that effect?

Placing both in the same freezer will mitigate this effect.

I suspect when tests are run individually or in separate freezers, the mechanism you propose is often what causes the hot sample to freeze in a shorted amount of time.

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I also suspect that different effects occur when both a hot an a cold sample are placed in the same freezer which can lead to the hot sample freezing first.

My guess is that a couple things are working in tandem:

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- The warmer sample melts through any frost to attain better contact with a shelf or support which is likely metal with good thermal conductivity. The support is in contact with a large thermal mass at below freezing temps and/or has significant surface area exposed to the freezer air.

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- Convection driven up and away from the hot sample is likely to deposit an insulating layer of frost preferentially upon the cooler sample...impeding heat transfer.

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- Early in the process, the hot sample is likely to drive the temperature and humidity up in the freezer. Even though this is likely to trigger the circulation of air and removal of heat, the temperature may not be below (or much below) the temperature of the cooler sample, for some time. By the time the a temperature below freezing is attained in the freezer air, other effects such as those mentioned above and things such as inertia convection currents in the hot sample, may provide all that is necessary for the hot sample to freeze first.

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The problem with this claimed effect is that lack of specificity in scientific terms. That hot water sometimes takes less time to freeze than cold water when placed in a commercial freezer, isn't really deserving to be titled a named 'effect'.

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If a claim were made using scientific units of measurement, I would give it a lot more leeway. I just don't think that a strong case can be made that the behavior of water with regards to specific heat varies significantly from our understanding in the parameters traversed in this type of experiment.

Aristotle described fisher folks using hot water as an "ice solder" to hold their rods in place when ice fishing.

No container.

I liked his concept of intuitively opposing trends causing an accelerated progression.

This is a load of b****cks: Lyn is right.

In earlier reports Mpemba acknowledged that the only effect he had seen was that the hot ice cream cartons melted the frost which formed an insulating layer on the bottom of the freezer compartment.

This point appears to have been deliberately made insignificant in the current wiki article.

Absolutely correct on all points.

Good comments from PFR and from Codemaster. What I was getting at in my first comment is : That we should strive to do experiments under controlled conditions that can be repeated. In this way one can compare like to like. And one may rule out suspect factors (Best done one at a time).

Once we start changing the conditions or altering the starting point then the picture becomes more and more cloudy. This way we loose track of what is causing what.

Note : In practice (eg in comerial New Product Development), we don't always have enough time and money to pursue each factor endlessly. In such commercial R&D, we often have to reduce the number of steps in our search for answers. We often have to make a decision to close down a certain avenue of ideas because of economics.

It is possible that the phase transition from vapor to liquid has an effect on the temperature of the environment above the water.Latent heat is released when changing from vapor to liquid, and this heat is also removed from the surface of the water below.The falling condensate also creates a microscopic "rain storm" on the surface of the water, which agitates the surface on a molecular level, causing a more efficient exchange of heat at the surface interface between the air and water.(More effective surface area)

It is also known that water expands when it freezes,and perhaps the phase transition from vapor to solid proceeds much faster when the molecules are at the proper"spacing" for ice to form.This could indicate a kind of "inertia" of the phase change property:When the water rapidly changes from vapor to liquid, the temperature continues to drop into the next phase: solid.

It would be interesting to be able to plot the temperature in real time of the two containers as they freeze, both inside and outside, and look at the slope of the temperature drop.I speculate that there is a longer "flat spot" where the water is at 0 degrees C,but not yet solid,in the cold water than the hot.

I would speculate that there is also some microscopic sublimation going on in the surface above the liquid.

On another vein, water vapor is lighter than air, and the surface of the hot water is covered by water vapor,which reduces the boiling point of the water which leads to more heat loss at the surface when compared to the cold water.

As the water condenses,it falls back into the container, not much water is lost,but it has removed some heat in the process.Very similar to clouds in the macro world.

It is possible that the phase transition from vapor to liquid has an effect on the temperature of the environment above the water.

yes, its I'm sure boundary layer are happening that may have an insulating effect?

.....The falling condensate also creates a microscopic "rain storm" on the surface of the water, ......

don't know about that. But I'll share from my observations, do not know the relevancy.

A few years ago, I loved frosted mugs. I'll put in the freezer a prepped mug where vapor was clearly visible when I put them in the freezer.

Well before the summer was out, I had to defrost the freezer because of the ice build up in the freezer.

So after all of this is said...

Should I connect the icemaker feed line to a hot water pipe?

I believe that is the normal convention, believe it, or not.

In my considerable experience with ice maker output, I've found that once the bucket is full, my consumption of cubes is the limiting factor, not the supply.

How long it takes the cubes to form matters not, as long as there's enough in the bucket for my gin and tonic(s).

Hey, whats so funny about that.........

Years ago, a girl I was dating, I hooked up her refrigerator icemaker lines on the apartment she was renting. The plumbing was a spegetti nightmare. After double checking twice, ^{(Lets see, yes that was (4) times)} I still hooked up the icemaker lines to the hot water. .

btw, I notice on her faucetts handles, 'C' means Hot and 'H' means cold.

'...btw, I notice on her faucetts handles, 'C' means Hot and 'H' means cold.....'

Perhaps it is Spanish? Agua caliente y agua helada.

si'

Is that that "South of the Equator" thing again?

Once again!

_{<unsubscribes>}

There is a reported fourth state of water called the Gel state where the water behaves as a gel. Dr Pollock has reported such phenomenon and refers to a zone of water where such states can occur as exclusion zones (EZ). An exclusion zone is a highly negative charged area and is found wherever water interfaces with a suitable material. The EZ will exclude most other anions and cations providing a very pure water zone. Water with a lower TDS or lower gas concentration will freeze quicker than those areas with higher concentrations. Salt water in the ocean may not freezer until you reach minus 3 degrees C while fresh water freezes at 0 degrees C. The lowering of the gases would occur by heating and then cooling water. However, the TDS will concentrate, ever so little, by simple heating due to evaporation of water. It makes me wonder if the EZ is increased a bit more by the heating process thus providing a thicker layer of pure water. There is a reported EZ at the interface with water and air and that may have something to do with the freezing of water at the surface first. It is a phenomenon that is real but still not understood to complete satisfaction. I would posture that the answer to OP's question lies in the understanding and exploration of the physics of the EZ in water.

Mazhur, just name the bar where we can get the free beer.

My building just got an ice palace full of ice sculptures. The sculptors told me definitely that water that had been heated makes the best, clearest ice. I'm not sure if they said it froze quicker, I'll try to find one to ask, but they went back to Lithuania.

My personal off-the-wall thought is I wonder if 'rate' comes into play. Can there be such a thing as 'rate of cooling' that comes into play when two containers of water are placed in the same freezer, one hot, one cold.

The hot one is going to have a greater temp differential with the freezer, and a certain 'rate' of cooling is going to happen. This 'rate' is going to be different for the cold water.

If the 'rate' is really greater for the hot water, it may beat the cold water to the frozen state.

For my next experiment, I will need a tall tower, preferably slightly leaning.........

I could not find a single scientifically designed experiment that demonstrates this. It has all of the makings of an urban legend. Ice cream makers use hot ice cream mix in their freezers not because it freezes faster, but because it is faster than cooling it off, and then making ice cream. They want some ice cream, get it? Cold ice cream mix (pre cooled,) most certainly turns to ice cream faster than hot Ice cream mix. I make it all the time in my Cuisenart. If I don't pre cool it, it takes forever.

About.com states that in many instances, cold water freezes before hot water. They don't know why.

It boils down to (no puns) the broad definitions employed in creating this seemingly brain twisting topic. I would love some one to post data, apparatus and technique. I've already burned an hour, and can find site after site that says, "as unlikely as it seems" blah blah blah blah. Here's why, we think. But no real data.

Boiled water is said to be 'biologically dead' water. Similarly when water is heated or is hot it is ousted of some or all of its oxygen which may tend to change its nature as compared to fresh or cool water. This might be the reason for quicker cooling of hot or boiled water when frozen at an initial room temperature.

If taken for granted that microwave brings changes in the molecular position of water during heating it may also be deduced that exactly the same might happen when tepid or hot or boiled water is subjected to cooling. I am not sure about it but microwave heating when thought in reverse heat transfer tends to furnish some food for thought on this subject...

Have a look...

http://www.wimp.com/microwaveoven/

When water vapor is cooled suddenly, it can sublime, that is, change directly into ice from a gas, bypassing the liquid state.This is what happens in a snow storm.

When this ice contacts the water surface, it absorbs heat from the water, as it changes into a liquid state.This cooling will occur in addition to the normal heat exchange processes going on , so the hot water is cooled by 2 phases of heat exchange, rather than one.

This is occurring on a very small scale, but the effect is large.The water is more quickly cooled by having given up heat to the ice and to the air above the water.

If the water is cooled very slowly, at say 31 degrees F, the effect would be less dramatic than at a lower temperature where sudden cooling of the vapor and resultant subliming can occur.

Any physics experts wish to comment?

The most pertinentexplanation I found in different sources is the fact that hot water has less gas in solution. Presence of gas molecules is a kind of barrier for water crystal continuity thus it takes more time for cold water. The rate is only at start higher for hot water but after a time it becomes as the one for cold water (when water temperature decreases enough). There are 2 aspects to consider : the amount of energy to evacuate via convection via the wall container convection and how water when cooled behaves. Hot water contains more heat but the melting energy for ice is the same for cold or hot water. IMHO only the presence or absence of elements disturbing the lattice growth can be the reason. What is BAD is nowhere is the full experiment description to be found with all details.

I remain unconvinced that the effect is real, if all the precautions (as covered in this thread) to ensure there's a like-for-like comparison, are taken. Anybody agree?

I'm still curious about the 'rate' factor. In weight in motion, there is momentum, or inertia, where a weight continues after force is removed. In gravity, there is an acceleration of speed increasing per-second-per-second.

Could such a phenomenon be available in heat transfer???

That did occur to me, but I can't think of any mechanism how inertia would apply to heat transfer. But perhaps somebody else can.

If you consider a recipient filled with a fluid the heat transfer occurs at the wall and/or at the surface. Let us look first at the wall. If the wall becomes colder then the fluid will also become colder in the near to the wall layer and thus heavier, it will flow down-wards. because of this flow in the center a compensation flow will come upwards.

This flow pattern will continue as long as the fluid did not reach it crystallisation temperature. Of course since viscosity is also temperature dependent the flow velocity will change, decreasing over time. If the heat is lost as well via the upper surface and/or the bottom the flow pattern will be more complex and a kind of circulation islands will be generated.

The same phenomenon occurs in the earth with flows from the crust to the center and vice versa. Displacement of plates is due to those flows. I have seen the result in Island where two plates part and one can see very well where it happens.

Concerning the problem we discuss there is an aspect which can be related to those flows. If water is hot the velocity can be higher and since water has a low viscosity it could be higher even if the temperature sinks. this could lead to better uniformity of temperature in the fluid and broader regions reaching at same time the transient from fluid to solid. In the absence of the disturbing gas molecules this could lead to a faster passing to ice.

Hi,

I've been gone, but the reference to flowing downward on the inside of the container reminds me of a properly poured glass of Guinness.

It seems to me that one has to impose too many artifical conditions on the subject of the experiment (water) to obtain the desired results.

For any reasonalbe person to related it to natural conditions and consider it a "natural occurrance" is not logical.

To borrow a line from "The Best Little Whorehouse in Texas", "Don't pee in my boot and tell me it's raining".

Maybe ignorance is bliss.

Why does water expands when freezinc? The same riddle, isn't it?

No, that is well understood. When water freezes it forms a molecular lattice structure that actual takes up a slight bit more volume that water molecules do in the free liquid state.

Precisely, it has something to do with arrangement and intermolecular freedom of movements. Somewhere in the transient phase of cold water to ice, molecules contracts and are restricted to freely moved, heat transfer is somewhat function of contact surface areas and convection.

In Hot water, molecules tend to expand(surfaces areas expand) and convection between them is at high rate. This explained when hot water is cooled it will freeze faster than cool water.

Conversely speaking, try to cook unthawed chicken, the same phenomena could be observed.

trying to cook unthawed chicken, in analogy, would theorize that it would cook faster than thawed chicken, implying that the enhanced heat exchange would result in reduced cooking time (or time to required to achieve target temperature) (which may or may not meet your definition of cooking).

Your statement that hot water when cooled (no temperature offered) will freeze faster than cool water (no temperature offered) is not only unprovable, (no data) it smacks of an intentional omission of data. I believe this is at the heart of this OP.

nope, you got the wrong point. Water as it freezes decrease thermal conductivity, that is why it would make marine life possible with such property. Why is sea not all frozen in winter?- It acts as insulator at the surface. That is the reason why it happened.

As to the chicken, unthawed chicken is definitely hard to cook than the thawed one because of the same reason.

Thermal conductivity of water is a function of temperature, it so happen that at higher temperature, water is more thermal conductor than at lower temperature, so to speak.

That's the mechanism, but it doesn't explain why it happens. Water is highly unusual in this respect (and in some others). If it contracted on freezing like most liquids, life would be very different, if it got started at all.