Author Topic: Freezing Speed of Hot Versus Cold Water  (Read 10752 times)

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Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #25 on: February 21, 2022, 12:06:53 am »
The Mpemba effect is real.  See e.g. Takada, Hayakawa, Santos, "Mpemba effect in inertial suspensions", Phys. Rev. E 103, 032901, 2021-03-08.  The only disagreement is whether it applies to water or not.  Given sufficiently rapid cooling in the experimental setup I described in my previous post in this thread, it can be shown to exist in water.  Anyone claiming otherwise is not sufficiently aware of the peer-reviewed articles on the subject within the last decade or so.  Many papers exist that claim otherwise, but suffer from incorrect assumptions or insufficient cooling rate, and extend the logical result (that the effect does not occur in these conditions) illogically into "the effect does not exist".

At the core of the real Mpemba effect is that heat capacity is not constant in non-equilibrium states.

It is well known that for solids, heat capacity is dependent on the lattice structure.  Essentially, latent heat - energy stored in the material without affecting the temperature of the material –, is associated with the phase change: the change in structure.  Water ice itself has at least nineteen different phases.  Note that while many can only be produced in specific (high) pressures, some of them can remain stable well outside their formation range.  Given temperature and pressure, there is often more than one stable phase.  Indeed, at the triple point, the solid, liquid, and gaseous phases are all in dynamic equilibrium.

For liquid water, the situation is more complicated, because any molecular structures involved are temporary and unstable (with the most stable ones, like water methane clathrates, involving other molecules), and the really interesting physics involves the properties of individual water molecules; the hydrogen-oxygen bonds (and to a lesser extent, the hydrogen-hydrogen bonds) in non-equilibrium states, when cooled or heated rapidly.

To simplify what happens in the real Mpemba effect, is that the liquid at hand is far from an equilibrium state, and because of recently been at much higher temperature, can lose heat energy much faster than the same liquid at the same temperature in an equilibrium state would.  Simply put, the recently-hot liquid has smaller heat capacity.  (The reality is more interesting, especially when the sample starts getting nearer to an equilibrium state of the heat bath, as localized heating can often be detected due to the latent heat.  But close enough for an intuitive understanding, the interesting parts and the actual mechanism, are more like technical details.)

If we had some kind of device or meter that could measure the net energy flow between the heat bath (freezer) and the (originally liquid) sample, we'd find that at the same temperature, the energy flow from the recently-hot sample to the heat bath is higher than for the sample that was not originally that hot.

In other words, there is nothing really odd here, just a variation in the heat capacity, depending on whether the water sample was really hot (boiling) or not.  Nothing anomalous in the everyday life sense, just an interesting physical phenomena.

I am actually a materials physicist (or close enough; I never submitted my thesis on ferrochrome structure providing the corrosion resistance effects), specialized in the numerical simulation aspects.  The Mpemba effect is interesting, because it was only in the last decade or so that we could numerically simulate the effect; and do so with multiple different classical chemical force-field potential models.  (Because of the large number of electrons involved [two per molecule, with hundreds of molecules minimum needed due to periodic boundary conditions inherent in ab initio simulations], and the difficulties in modeling hot water in ab initio simulations, the entire phenomenon hasn't been simulated ab initio (using e.g. VASP, Dalton, Siesta, or similar) thus far, only at specific temperatures showing the differences in the molecular structure of each water molecule, supporting the observations in simulations using classical force-field models.)
 
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Offline CatalinaWOW

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #26 on: February 21, 2022, 12:26:51 am »
Nominal I have to disagree with just one thing in your response.  The idea that a liquid can have different states with different properties that are stable enough to have macro effects is weird, wonderful and yes, odd.  I guess your extensive experience modelling this makes this strange phenomena seem commonplace to you.

I put this in the same category as super-cooling, which though common enough under certain conditions is certainly generally uncommon and odd.  My son and I were greatly fascinated on a recent vacation when the freezer at the hotel would routinely super cool water bottles.  They could be removed from the freezer and were completely liquid, but a simple rap on a countertop would cause them to freeze solid in a few seconds.  Watching the freeze front chase through the liquid while the bottle was certainly gaining thermal energy from our relatively warm hands was one of the high points of the vacation.  But as relatively repeatable as this was in that set of circumstances, it is the only time in seven decades that I have actually observed the phenomenon.  And even there it only happened in perhaps a dozen bottles out of a couple dozen that were frozen.
 
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Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #27 on: February 21, 2022, 12:53:56 am »
Nominal I have to disagree with just one thing in your response.  The idea that a liquid can have different states with different properties that are stable enough to have macro effects is weird, wonderful and yes, odd.  I guess your extensive experience modelling this makes this strange phenomena seem commonplace to you.
Not commonplace.  And I would be very surprised if it did happen in equilibrium conditions, without significant energy flow in/out.

I meant more in the sense of anomalies or strange phenomena as used in e.g. History channel TV shows.

I put this in the same category as super-cooling, which though common enough under certain conditions is certainly generally uncommon and odd.  My son and I were greatly fascinated on a recent vacation when the freezer at the hotel would routinely super cool water bottles.  They could be removed from the freezer and were completely liquid, but a simple rap on a countertop would cause them to freeze solid in a few seconds.  Watching the freeze front chase through the liquid while the bottle was certainly gaining thermal energy from our relatively warm hands was one of the high points of the vacation.  But as relatively repeatable as this was in that set of circumstances, it is the only time in seven decades that I have actually observed the phenomenon.  And even there it only happened in perhaps a dozen bottles out of a couple dozen that were frozen.
Funnily enough, the only requirement for that to happen is that the water does not contain seed kernels, either surface defects in the container, or "impurities" in the water that the freezing process can start from.  Boiling the water, then bottling it while relatively hot, is often enough to remove the seed kernels.

The same can also occur when boiling water, especially when boiling water in a glass or glazed ceramic cup or mug in a microwave oven.
When you take the water out from the oven, it is steaming hot, but does not boil.  Drop a spoon in it, and it basically explodes, boiling all at once.

You are absolutely right in that this does belong to the same category, though.  In these cases, the water is not really in an equilibrium condition; it is in a meta-stable state, where a tiny little nudge in the parameter space is needed for the entire system to roll down into a more stable and closer to equilibrium state.  In the case of superheated or supercooled water, something needs to start the phase change reaction; after which the entire sample will change states almost at once, in a continuous wavefront, like Dominoes falling.

In liquid water, in the Mpemba effect, it is the energy flow (heat flowing out of the sample) that maintains the non-equilibrium properties of the water molecules.  In the simulations, it can be seen how the energy is lost in molecular interactions ("collisions") isn't equally distributed in the degrees of freedom; that it takes considerable time (considering typical time steps are in the femtosecond range, 10-15 seconds per time step) for each water molecule to "relax" to something close to an internal equilibrium state after each collision.  Both when the molecule loses or gains energy from the collision, too.  In this non-relaxed state, the chemical properties of the molecule, including heat capacity, differs from that when it is in relaxed state.

Put another way, if you somehow isolated one water molecule in the middle of the Mpemba effect, even without any energy flow in/out, the temperature and heat capacity of that molecule would still change, until it reached the relaxed state (in equilibrium with its surroundings).  (I have no idea how long that would take.  There are different simulations for different time scales, and I am not aware of any work trying to find out how fast that internal relaxation takes.  I know of a few methods how one could start to find out –– from the average collision interval between water molecules at standard pressure at different liquid temperatures –– but no idea if anyone has done the work needed.)

Water methane clathrates are similar, in that e.g. an earthquake (at the continental shelf at arctic or antarctic latitudes) is enough to make the clathrates release the methane into the water and from there to the atmosphere.  They, too, tend to be supercooled, in the sense that they stay liquid although their temperature is less than the freezing point of water.  (In tropical latitudes, methane tends to be generated in the seabottom mud due to biological reactions, with the organic mud forming a more or less methane-impermeable layer.  When the methane pocket pressure becomes high enough, it bursts through the mud.  No clathrates are involved there.  These methane pockets/bubbles, by the way, are suspected to be the reason for a few sunken ships in the Sargasso Sea near Bermuda, by the way; if the water is deep enough for the methane to mix into the water, it reduces the water density, and therefore the buoyancy.  The Sargasso weed itself, decaying at the seabottom, being the source for the methane.)
« Last Edit: February 21, 2022, 12:58:08 am by Nominal Animal »
 

Offline T3sl4co1l

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #28 on: February 21, 2022, 02:40:55 am »
Holy shit, you mean "structured water" actually exists?! -- Just, not in anything like the fantastical claims usually ascribed to that term, just in the more mundane matter of heat capacity -- in other words, that there's, apparently, degrees of freedom which don't equilibriate quickly with the bulk.  And it's not like, nuclear spins, obviously, which wouldn't have nearly enough heat capacity to be sensible (even in a strong magnetic field(?)), and yet, with an equilibrium time constant on that order?

Mind blown.

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Offline CatalinaWOW

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #29 on: February 21, 2022, 03:04:30 am »
The boiling out of a microwave phenomenon is widely reported, but uncommon enough that no one I have spoken to has personally encountered it.  These things show how inadequate terms like easy, common, rare and the like are to make useful decisions about risk and necessary precautions.  I have no idea how likely these events actually are.
 

Offline IanB

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #30 on: February 21, 2022, 03:28:01 am »
At the core of the real Mpemba effect is that heat capacity is not constant in non-equilibrium states.

What do you mean by "equilibrium state"? Thermal equilibrium? Mechanical equilibrium? Chemical equilibrium?

Furthermore, heat capacity is not constant. You do not have to qualify this. Specific heat capacity is a function of many variables, notably temperature.

However, setting all this aside, if you start out with 1 kg of water at 100°C and 1 kg of water at 25°C, and place them in identical containers in identical cold surroundings (for example still air at 5°C), then the water that starts our cooler will remain cooler for as long as you wait. The hotter water will never overtake it.
 

Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #31 on: February 21, 2022, 05:03:27 am »
Holy shit, you mean "structured water" actually exists?!
Not really, no, because the structures themselves do not last, and it is more to do with individual water molecules' degrees of freedom (specifically, the one corresponding to the lengths of the hydrogen-oxygen bond) than molecular structures per se.  The forces that form the molecular structures are much weaker than the molecular bonds between the oxygen and hydrogen atoms, best approximately described as Van der Waals forces.

(The molecular structures "observed" in simulations is typically a result of using too few water molecules, and periodic boundary conditions.  Essentially, the simulated volume is too small, and un-physical structures can pop up because of artificial effects due to the boundary conditions.)

Even though weak, the traditional example of showing how such weak forces can become observable in the macro scale, is to bring a magnet (or something with a static charge) close to running water running from a faucet: the stream bends, because each individual water molecule is polar.

To simplify A LOT, the core feature with water seems to be (based on simulations matching the experiments) that the hydrogen-oxygen bond length varies slower than the angular vibrational degrees of freedom.  Because the potential energy function is not symmetric, it takes "significant" amount of time for the energies in the different degrees of freedom to find the internal equilibrium state corresponding to Boltzmann distribution.

Simply put, when water molecules with different velocities and internal kinetic energies interact, the vibrational degrees of freedom are coupled better than the degrees of freedom related to the bond lengths, and it takes appreciable time for the internal kinetic energy distribution across the degrees of freedom to relax to the expected distribution.

When water molecules with very different energies (at very different temperatures) interact, the interactions tend to enforce that disparity rather than smooth it out.  Atoms and molecules do not actually collide like marbles; the outermost interacting electrons interact instead.  The end result can be treated like collisions, usually.  But, when you have polar molecules or complex molecules like proteins, these interesting effects can become measurable at the macro scale.

Mind blown.
Anyone having done any numerical simulations dealing with water molecules, has an intuitive grasp of how complex water chemistry really is.

So much so that when you first suggest simulating water molecules, every experienced numerical simulation person will be taken aback a bit, and will ask you if you realize how complicated and computationally-heavy task that is, especially compared to e.g. metals like iron or copper.

At the core of the real Mpemba effect is that heat capacity is not constant in non-equilibrium states.

What do you mean by "equilibrium state"? Thermal equilibrium? Mechanical equilibrium? Chemical equilibrium?
Thermal equilibrium.  Given fast enough heating or cooling, the heat capacity of a water molecule at a specific "temperature" (kinetic energy) will depend on its recent "temperature", because the kinetic energy within the molecule is distributed asymmetrically in the internal degrees of freedom, and it takes a relatively long time for the kinetic energy to reach the distribution among the degrees of freedom described by Boltzmann.

However, setting all this aside, if you start out with 1 kg of water at 100°C and 1 kg of water at 25°C, and place them in identical containers in identical cold surroundings (for example still air at 5°C), then the water that starts our cooler will remain cooler for as long as you wait. The hotter water will never overtake it.
That is what you believe.  Yet, it is not exactly true.  In still air, yes, because the cooling effect is not fast enough for Mpemba effect to occur.

However, if we use a heat bath with sufficient surface area to speed up the heat flow, based on the peer-reviewed articles I've read, it is possible for the originally hot water to become temporarily cooler than the other water sample.

This effect occurs, when the energy flow from the originally hotter sample to the surrounding heat bath is faster than from the originally cooler sample at that same temperature.
 

Offline IanB

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #32 on: February 21, 2022, 08:40:32 am »
Thermal equilibrium.  Given fast enough heating or cooling, the heat capacity of a water molecule at a specific "temperature" (kinetic energy) will depend on its recent "temperature", because the kinetic energy within the molecule is distributed asymmetrically in the internal degrees of freedom, and it takes a relatively long time for the kinetic energy to reach the distribution among the degrees of freedom described by Boltzmann.

Sorry, but this is not any kind of recognized or accepted physics or thermodynamics. There is no such thing as "temperature", there is only temperature. And a single  water molecule does not have a temperature or a heat capacity. Temperature is a macroscopic phenomenon resulting from averaging on a non-quantum scale.

What you can accurately say is that any system where heat is flowing is not in equilibrium, and also any system where the temperature varies from one point to another is not in equilibrium. But these are both macroscopic observations and do not have anything to do with individual molecules.

Quote
That is what you believe.  Yet, it is not exactly true.  In still air, yes, because the cooling effect is not fast enough for Mpemba effect to occur.

However, if we use a heat bath with sufficient surface area to speed up the heat flow, based on the peer-reviewed articles I've read, it is possible for the originally hot water to become temporarily cooler than the other water sample.

I sincerely doubt that such peer reviewed articles appear in mainstream physics journals, or if they do, you are misinterpreting what they are saying.

Quote
This effect occurs, when the energy flow from the originally hotter sample to the surrounding heat bath is faster than from the originally cooler sample at that same temperature.

The laws of thermodynamics say that the heat flow depends on the temperature difference. If two samples have the same temperature difference with the surroundings, then all other things being equal the heat flow is the same. If the heat flow is different, then the temperature is different.

You have to keep in mind that if you try to cool something down fast, it becomes even harder to get the heat out of it. Because you will rapidly cool down the outside surface while the interior remains warmer due to the limits of thermal conductivity.
 

Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #33 on: February 21, 2022, 10:28:55 am »
I'm trying to explain things in a way that laymen understand it.  Feel free to nitpick.

I sincerely doubt that such peer reviewed articles appear in mainstream physics journals, or if they do, you are misinterpreting what they are saying.
If you had bothered to read any related articles before spouting your beliefs, you'd have known better.  My previous posts in this thread – which you obviously didn't bother to read, just posted your superior beliefs – even had links to related articles.  For even more focused support for my arguments, see e.g.
Zhang et al., "Hydrogen-bond memory and water-skin supersolidity resolving the Mpemba paradox". Phys. Chem. Chem. Phys., 2014, 16, 22995-23002. Arxiv preprint.
Lu, Raz, "Nonequilibrium thermodynamics of the Markovian Mpemba effect and its inverse". PNAS May 16, 2017 114 (20) 5083-5088. PDF.

There is no scientific consensus yet, but the above definitely support my argument here, and are quite mainstream.
« Last Edit: February 21, 2022, 10:30:51 am by Nominal Animal »
 

Offline magic

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #34 on: February 21, 2022, 10:51:13 am »
To simplify what happens in the real Mpemba effect, is that the liquid at hand is far from an equilibrium state, and because of recently been at much higher temperature, can lose heat energy much faster than the same liquid at the same temperature in an equilibrium state would.  Simply put, the recently-hot liquid has smaller heat capacity.  (The reality is more interesting, especially when the sample starts getting nearer to an equilibrium state of the heat bath, as localized heating can often be detected due to the latent heat.  But close enough for an intuitive understanding, the interesting parts and the actual mechanism, are more like technical details.)

If we had some kind of device or meter that could measure the net energy flow between the heat bath (freezer) and the (originally liquid) sample, we'd find that at the same temperature, the energy flow from the recently-hot sample to the heat bath is higher than for the sample that was not originally that hot.
That makes no sense. You are now making claims about the container or surrounding environment having higher thermal conductivity because it "knows" something about the water inside.

Reduced heat capacity means that at the same temperature and the same energy flow, dT/dt is faster. Not quite as you explained it.

Another explanation you could reasonably attempt is increased thermal conductivity of water, i.e. less internal gradient across its volume.
 

Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #35 on: February 21, 2022, 01:49:14 pm »
That makes no sense.
Then read the linked paper.
 

Offline magic

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #36 on: February 21, 2022, 04:01:19 pm »
It's not the paper which made the statement that two samples at the same momentary temperature are conducting different amount of heat through (presumably) identical containers to (presumably) identical external environment. That's a statement about containers, not about water.
 

Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #37 on: February 21, 2022, 06:44:46 pm »
It's not the paper which made the statement that two samples at the same momentary temperature are conducting different amount of heat through (presumably) identical containers to (presumably) identical external environment. That's a statement about containers, not about water.
Sigh.

Here's a snippet from the abstract of the Zhang et al. paper:
Quote
Numerical reproduction of observations, shown herewith, confirms that water skin supersolidity [Zhang et al., Phys. Chem. Chem. Phys., DOI: 10.1039/C1034CP02516D] enhances the local thermal diffusivity favoring heat flowing outwardly in the liquid path. Analysis of experimental database reveals that the hydrogen bond (O:H–O) possesses memory to emit energy at a rate depending on its initial storage. Unlike other usual materials that lengthen and soften all bonds when they absorb thermal energy, water performs abnormally under heating to lengthen the O:H nonbond and shorten the H–O covalent bond through inter-oxygen Coulomb coupling [Sun et al., J. Phys. Chem. Lett., 2013, 4, 3238]. Cooling does the opposite to release energy, like releasing a coupled pair of bungees, at a rate of history dependence. Being sensitive to the source volume, skin radiation, and the drain temperature, the Mpemba effect proceeds only in the strictly non-adiabatic ‘source–path–drain’ cycling system for the heat “emission–conduction–dissipation” dynamics with a relaxation time that drops exponentially with the rise of the initial temperature of the liquid source.

Note the part where it mentions "Cooling [releases] energy, [...] at a rate of history dependence"?

The skin supersolidity is a related phenomenon discussed for the last decade or so, starting at Sun, et al. "Density, Elasticity, and Stability Anomalies of Water Molecules with Fewer than Four Neighbors". J. Phys. Chem. Lett. 2013, 4, 15, 2565–2570. https://doi.org/10.1021/jz401029z.
 

Offline CatalinaWOW

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #38 on: February 21, 2022, 06:49:16 pm »
To simplify what happens in the real Mpemba effect, is that the liquid at hand is far from an equilibrium state, and because of recently been at much higher temperature, can lose heat energy much faster than the same liquid at the same temperature in an equilibrium state would.  Simply put, the recently-hot liquid has smaller heat capacity.  (The reality is more interesting, especially when the sample starts getting nearer to an equilibrium state of the heat bath, as localized heating can often be detected due to the latent heat.  But close enough for an intuitive understanding, the interesting parts and the actual mechanism, are more like technical details.)

If we had some kind of device or meter that could measure the net energy flow between the heat bath (freezer) and the (originally liquid) sample, we'd find that at the same temperature, the energy flow from the recently-hot sample to the heat bath is higher than for the sample that was not originally that hot.
That makes no sense. You are now making claims about the container or surrounding environment having higher thermal conductivity because it "knows" something about the water inside.

Reduced heat capacity means that at the same temperature and the same energy flow, dT/dt is faster. Not quite as you explained it.

Another explanation you could reasonably attempt is increased thermal conductivity of water, i.e. less internal gradient across its volume.

The way I read Nominal's comments you have hit upon what he is saying.  The water loses heat faster.  Which would indeed slow heat transfer through the container.  But if the heat transfer through the container is not the dominant term you get the observed effect.  Remember that it is observed and repeatable (albeit with care and difficulty).  Arguments about possibility are just silly unless you are invoking experimental error.  That invocation requires supporting data just as anything else would.  Nominal has provided a credible theory, which may or may not be what is really going on, but can be modelled and fits the data.
 

Offline m k

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #39 on: February 22, 2022, 11:41:09 am »
Take hot enough water and sling it up to cold enough air and you get ice dust.
If you're under and temperature difference is not enough you'll get wet.
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Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #40 on: February 23, 2022, 01:23:11 am »
I completely forgot, and I've actually done it in real life! :palm:

Here is Viva Frei doing it on Youtube:
 

Offline IanB

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #41 on: February 23, 2022, 01:59:05 am »
That's a cool video, but it doesn't break any laws of physics. Calling it the "Mpemba effect" is just a clickbaity title to get views.
 

Online bdunham7

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #42 on: February 23, 2022, 02:23:37 am »
That's a cool video, but it doesn't break any laws of physics. Calling it the "Mpemba effect" is just a clickbaity title to get views.

This is why snow machines use hot water...oh, wait...
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #43 on: February 23, 2022, 03:59:08 am »
That's a cool video, but it doesn't break any laws of physics.
Neither does the effect discussed, even if you believe otherwise.

Next time you are somewhere cold enough, do the same with both hot and cold water.  Then come back and say that your results have nothing to do with the effect discussed here, even though only the hot water turned to ice mist, and the cold water remained as liquid droplets.

This is why snow machines use hot water...oh, wait...
Ha, ha.  Forgot about total energy?  You know, the electricity or fuel you pay for when using snow machines?

That was a pretty dumb post from you, I must say.



This thread is making me really depressed, to be honest.  So much "I don't believe you, because it is not how I believe things to be", instead of just checking out the peer-reviewd articles and studies by actual chemists and physicists.  Just "Because I cannot believe you, you must be wrong" type of arguments, and references to people who constructed a test setup where the phenomenon does not occur, and assume that must mean that the phenomenon does not exist.  No true counterarguments, just throwaway claims of "this violates that", without any basis for such claims beliefs.  None of this violates any of thermodynamics or anything else; I've even explained the most likely mechanism exactly how and why this happens above (with links to the underlying articles that supports that argument).

Do you not realize when your arguments are not science, but religion?  Dammit, I'm out.
 

Offline TMM

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #44 on: February 23, 2022, 04:05:01 am »
If you control everything other than the temperature of the water then once the water reaches the same temperature as the cold water, it can only take the same amount of time as the cold water to freeze. Claiming otherwise is claiming that the water has a memory effect. Of course in practice it's very difficult to control every variable other than the water temperature as the temperature of the vessel and surrounding air will not be the same after chilling the hot water to a cool temperature, as compared to the cool water's initial starting point. The hot water vessel and surrounding air are likely to be much cooler when the water contained reaches the 'cool' temperature and is continued to be chilled, as compared to the vessel that starts off with 'cool' water and just begins to be chilled. If the vessel and surround air are already cooler when the 'hot' water reaches the 'cool' temperature, then you'll be extracting heat from it at a faster rate than the cool water vessel that you have just begun chilling. Of course, you've wasted all the time/energy chilling it from hot to cool, so it can't possibly get to freezing faster than the cool water if you start chilling them at the same time. The time taken to get from hot to cool may be negligible compared to getting from cool to freezing, therefore any variance caused by not controlling all test variables perfectly may well let the 'hot' water freeze first for some test samples but if you do enough trials the average time to freeze should be slower for the hot water.

This is basically the same as claiming that a capacitor initially charged to 100V will discharge to 1V faster than one initially charged to 20V when you put the same value resistor across them. When the 100V capacitor has discharged to 20V it is in the same initial state as the 20V capacitor, therefore it can only take the exact same amount of time to go from 20V to 1V. The time taken to get from 20V to 1V is twice as long as from 100V to 20V so if test variables are poorly controlled (such as the value of the capacitor and resistor) it is possible for one capacitor initially charged to 100V to discharge to 1V faster than another capacitor initially charged to 20V...
« Last Edit: February 23, 2022, 04:17:56 am by TMM »
 

Offline IanB

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #45 on: February 23, 2022, 04:30:50 am »
This thread is making me really depressed, to be honest.  So much "I don't believe you, because it is not how I believe things to be", instead of just checking out the peer-reviewd articles and studies by actual chemists and physicists.

I'm not sure why you keep bringing up "peer reviewed", as if it conveys anything? There are many errors and omissions in published articles, and even plain bullshit in some cases.

If you can link to, or reference, one credible experiment where such an effect has been observed, then we can have a conversation.

So far in this thread, you have linked to articles describing mathematical and computer models that suggest, given suitable conditions, such an effect might be observed. This is not evidence, it is speculation.
 

Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #46 on: February 23, 2022, 04:50:07 am »
There are many errors and omissions in published articles, and even plain bullshit in some cases.
Point a single one, and stop bullshitting by making unfounded claims, and we can have an useful conversation.

What you have been posting, isn't science: it is assertion of unfounded beliefs.
 

Offline IanB

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #47 on: February 23, 2022, 05:09:14 am »
 
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Online bdunham7

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #48 on: February 23, 2022, 05:14:19 am »
Ha, ha.  Forgot about total energy?  You know, the electricity or fuel you pay for when using snow machines?

That was a pretty dumb post from you, I must say...

This thread is making me really depressed, to be honest.  So much "I don't believe you, because it is not how I believe things to be", instead of just checking out the peer-reviewd articles and studies by actual chemists and physicists.

Do you not realize when your arguments are not science, but religion?  Dammit, I'm out.

I've been avoiding this debate because I don't want to get sucked into another waste of time, but I now have an irresistible urge to call you out as a drama queen here.  You've taken a novel but arcane corner-case that might actually be interesting to a few people--including maybe even me-- and waved around a 'peer-reviewed' article that may or may not be meritorious but has a clickbaity title using 'Mpemba'.  To me, Mpemba is ice cubes in a freezer, period.  I realize he 'discovered' the effect making ice cream, but the ultimate question for me is whether I should use hot or cold water in my ice cube tray.  Go ahead, call me simple. If you bring up other situations that have obvious differences and claim they are somehow analogous, you should be ashamed of yourself considering how you claim to represent objective truth and reason.

My snow machine comment wasn't dumb, it was straight to the point.  When you toss boiling water in the air, the difference between that and cold water is not that the heat capacity of the hot water is temporarily (and drastically) reduced nor that some characteristic of the water has changed so as to reduce the enthalpy of ice formation from it.  The difference that does matter is resolved by the (non-heated) snow machine when it atomizes the water.  I think that neither the effect in your peer reviewed article nor in the snow video are going to matter in a more typical Mpemba experiment where you might take 90C and 10C water and cool it in a -20C freezer to equilibrium.  That--which the OP in this thread unfortunately did not do as he terminated the experiment too early--is where I believe you simply don't see the effect, or if you do it is due to other factors for which I'm not aware of any real consensus.  The PCCP article appears to address this, but I didn't read it in any detail. 

I think the whole issue can be simplified into two broad questions: 

If you form ice from hot and cold samples and cool it to some temperature well below freezing and you were to observe the Mpemba effect by the hot sample leading the way, is that due to the hot sample releasing less energy (less enthalpy) or due to the transfer of heat happening faster (or both)? 

If you observe the Mpemba effect, then at the end after they are cooled to say -20C, are the two samples in the same or equivalent state at the end with regard to enthalpy (and entropy) or are they in two different states?  So perhaps if I use hot water to make ice faster, that ice won't have as much cooling power?   ???


One thing to keep in mind is that if you start with a 90C and a 10C sample, classic assumptions lead you to the conclusion that the hot sample will need to release approximately twice the heat to form ice.  That's a big difference to account for.

« Last Edit: February 23, 2022, 05:28:50 am by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Nominal Animal

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Re: Freezing Speed of Hot Versus Cold Water
« Reply #49 on: February 23, 2022, 05:23:04 am »
I've been avoiding this debate because I don't want to get sucked into another waste of time, but I now have an irresistible urge to call you out as a drama queen here.
Fine.  I've downgraded my opinion of you to "too stupid to interact with".  You're welcome; the ignore list functionality is there for a reason.
 


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