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Freezing Speed of Hot Versus Cold Water
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Nominal Animal:

--- Quote from: IanB on February 23, 2022, 05:09:14 am ---
--- Quote ---We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect.
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Did you read the article?  The experiment was done by a single person, Henry C. Burridge, who furthermore redefined the effect:

--- Quote ---A reasonable start to analysing the problem is to consider the process in two stages; first, cooling the water to an average temperature of 0 °C (or enthalpy equivalent thereof), and second, freezing the water to form solid ice. In so doing any effects associated with the supercooling of water are entirely contained within the second stage. We restrict our definition of the Mpemba effect to the first stage of the process, i.e. the process of cooling a sample of warm water to 0 °C in less time than it takes to cool a sample of water, which is notionally identical except that it is initially at a lower temperature, to 0 °C.
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There is nothing reasonable in that approach, nor is it "notionally identical".   I do wonder how the reviewers let that pass, actually.

It is obvious that the phase change is a crucial part of the phenomena, because of conservation of energy (and how that relates to the latent heat and/or non-Boltzmannian distribution of energy in the degrees of freedom of each water molecule).  Indeed, one of the key points is to have a thermal bath well below the freezing point of water to even observe the effect.  (Why is this a requirement?  Consider the case where the rate of heat flow has to exceed some limit, before the effect can occur.  A typical flask or vessel does not have sufficient surface area [i.e. sufficient water skin to volume ratio] at something like 0°C to -15°Cfor the heat flow to suffice for the effect to occur.  To increase the rate, one can either increase the surface area to volume ratio, or simply use cooler heat bath, typically -20°C or colder (freezers).

Even if the heat bath is required to be much colder than the freezing temperature (and increasing surface area to volume ratio does not suffce), does not negate the existence of the effect; it'd just tell use something much more interesting about the phenomenon.

I shall assume all your other "counterarguments" are bullshit of the same sort, and will ignore you too.

There is nothing more I can tell people that actually matters, since the issue –– when and in which materials does the Mpemba effect occur –– has been sufficiently proven in my opinion, and arguments that are based on redefining the word to mean some other phenomenon are utter bullshit not worth discussing.
magic:

--- Quote from: Nominal Animal on February 23, 2022, 05:38:42 am ---I do wonder how the reviewers let that pass, actually.
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That's the exact problem with peer reviewed science.

There are competing groups of nerds coming up with weird ideas and each patting their own guys on the backs to secure further public funding :P
magic:
As for the effect itself, I'm afraid I don't care enough to read a dozen papers and try to figure out which side is more wrong and whether perhaps both are talking about the same thing in different terms ;)

My earlier objection was purely to your own "layman explanation" of the thing. Based on your response I believe that you believe the alleged effect to indeed be a combination of the two factors I mentioned: reduced heat capacity (faster dT/dt for equal energy flow) and reduced thermal conductance of water at the interface with the container (is this what they meant by "something something heat diffusion something skin supersolidity something"?).

So I guess you can say that two bodies of water at equal bulk temperature release energy at different rates, but it's not by magic, but by thermal insulation and lower temperature of the outer layer of water due to some stupid factors.

Maybe it's possible, who cares. Post a video for us, the lazy crowd ;)
T3sl4co1l:

--- Quote from: TMM 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.
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That's...exactly what he said though.  o.o

So, if I understand this effect correctly, it would indeed make snow faster (nevermind the expense of heating all that water), because the transient heat capacity is lower, heat transfer is normal, and as a result it freezes faster.  BUT, it would make a rather dense pack, or just not freeze very well at all, because the excess heat still has to come out at some point, sooner or later, and, I guess it's going to be mushy, or partially frozen or something until then?

How does that work anyway, does it actually freeze solid and the ice retains some anomalous heat?  Even though it's a completely different phase?

And that should mean, you can shock-cool water, and then it will warm back up over some time frame as that excess heat returns to the normal sensible mode.  Which is a very strange thing indeed for a substance to do, but not thermodynamically inconsistent at least.  (Remember: despite what the name might seem to imply, thermodynamics is only concerned with end states at infinity: "dyn" refers to the fact that it's the exchange of heat at all, not that it's the dynamics (time dependence, kinetics) thereof!)

I suppose an easily dissociated (low energy), but kinetically unfavorable, chemical could exhibit the same sort of response.  Don't know of any offhand, but I'm sure something like that exists...

Which, hot-ice packs are kinda like that, but that's due to heat of crystallization and happens suddenly on nucleation, not due to a kinetically hindered reaction that happens gradually.



--- Quote ---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.

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Doesn't it, though?

We need to develop the model a bit first though.  Consider the case of dielectric absorption.  We can discharge the capacitor immediately, delivering less energy/charge than it contains in total, the rest of which comes out more slowly.

This matches one aspect of the observation, but is also repeatable, from any voltage -- it's linear and time-invariant.  So we need some dependencies here.

If we make the ESR of the dielectric absorption dependent on voltage, we can have it so it charges quickly at high "temperature", but on "quenching" the main capacitance down to low voltage, it retains a lot.  (Maybe we make the resistance proportional to terminal voltage, for example.  Or more generally, some function like that.)

But this has the effect of merely varying the "heat capacity" with time and temperature.  To reproduce the effect of normal cold water having normal heat capacity, while quenched (previously-hot) water has low, we need another state dependence.

We could have a pair of fixed capacitances, modeling the anomalous plus remainder "heat capacities", plus an auxiliary C off to the side which represents the internal state.  C_aux might be arbitrarily small (i.e. just for modeling purposes, or not even connected to the component terminals at all -- a common SPICE motif, modeling auxiliary functions with respect to ground, connecting them to the main subcircuit by dependent sources), and its voltage would be coupled to the main terminals via resistor (possibly dependent again).  This could then have the effect that, for previously-cold water, C_aux is also "cold" so the dependent resistance is low and thus the total, nominal "heat capacity" is rapidly sensible; but if C_aux has been allowed to charge (i.e., it's coupled to the terminal voltage), then the remainder "heat capacity" becomes loosely coupled and is not rapidly sensible, thus reducing the transient heat capacity, until C_aux has discharged enough that the two main capacitances become tightly coupled again.  Note that, depending on how fast the C_aux dis/charges, nominal or anomalous heat capacity might be sensible at high temperature, or just over shorter time scales; depends on relative values.

Probably the same thing can be arranged from dependent (variable) capacitances as well, given suitable disambiguation of whether those should conserve charge or not (in SPICE for example, capacitance can just be some dependent source, no need to conserve charge; in reality, charge must be conserved and a reduction in capacitance causes an increase in terminal voltage), and possibly a fixed coupling resistance; maybe it still has to be dependent as well.

In any case, this can be drawn up fairly easily, given a differential equation for the system, and then you can have a capacitive sort of model to play with.



--- Quote from: Nominal Animal on February 23, 2022, 03:59:08 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.  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).

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It is unfortunate; I sympathize.  Unfortunately I don't have nearly enough reading into this subject to give much of a technical review of the papers linked; they have problems, to me, but not enough to say whether that rises to the level of supporting or contradicting the claim.  To wit: the one with simulations, begs asking whether the observed effect is realistic in nature -- and if it has anywhere near such a time constant as to be relevant (min vs. fs is an extraordinary claim, to be sure!).  Or if they're simulating anything relevant at all, which, I'm just not familiar enough with the subject to understand what exactly they're concluding from it.  Which is itself a valid criticism: it seems not well enough explained, at least at the depth of reading I did.  Which is far from a fatal error, it's a common shortcut within a field; but obviously, that also limits its audience to those within that field.  And the other paper, I think is just too abstract to relate to something so [seemingly] ordinary as water?  I didn't gather much from it, it's mostly an equations of state kind of thing?

So, I'm open to the phenomenon, and mechanism; but like I said, it's an extraordinary claim, and spanning 17 orders of magnitude with one mechanism requires a lot more motivation and explanation than I've seen here.  For comparison, consider the decay of singlet oxygen: an extremely prohibited transition (due to quantum spin transition rules), so it persists for a relatively long time (seconds), typically being catalyzed by intermolecular interactions, or impurities, which break the symmetry and ultimately extract that energy, allowing decay to the ground (triplet) state.  Such a remarkable and (nearly) "iron clad" quantum prohibition would seem necessary here -- but neither paper is presenting such a claim (and, I'm not aware of such states in bulk water -- again, not that I'm any kind of expert on that!).

Tim
m k:

--- Quote from: magic on February 23, 2022, 08:25:54 am ---
--- Quote from: Nominal Animal on February 23, 2022, 05:38:42 am ---I do wonder how the reviewers let that pass, actually.
--- End quote ---
That's the exact problem with peer reviewed science.

There are competing groups of nerds coming up with weird ideas and each patting their own guys on the backs to secure further public funding :P

--- End quote ---

There are also cognitive dissonances like confirmation bias.
One good example is Vera Rubin and Dark matter.

In this case there are also those ice-plus and ice-minus "organisms" clearing things.

That higher speed of battery charge by more parallel chemistry is not very old either.

BTW,
that video includes pretty simple and pretty statistical thing.
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