Freezing Speed of Hot Versus Cold Water - Page 1
Forum section: electronics / general

author: bostonman
author_rank: Super Contributor
timestamp: February 18, 2022, 04:01:36 am
content: Recently we had single digit temperatures approaching and decided to experiment with the freezing speed of hot versus cold water.From research, hot water should freeze faster, but I didn't exactly get these results.The outside temperature was approximately 20-25 degrees F (and deceasing slowly). I placed a piece of plywood across two sawhorses (to eliminate the ground from acting as a heat sink), placed two identical cookie tins on the plywood (spaced apart), used a piece of copper tape to hold the temperature probe on the bottom of each pan (I used two identical temperature data loggers), and, simultaneously poured tap water in one, and near boiling water in the other.If my understanding of thermodynamics is correct, large delta temperatures will cool quickly and then slower as it gets closer to the ambient air (I believe technically they will never be exact). As an example, if I heated a steal block so it was glowing red, and placed it outside in 0 degrees F, it will cool very quickly in the beginning, and then slower and slower until it almost reaches 0 degrees F.Having said this, if you look at my hot versus cold graph, the hot water seems to do just that. Leaving out the fine details such as just exactly what is going on with the molecules, from research, I expected the hot to freeze noticeably faster.Looking at the zoomed in graph around 32 degrees F, the hot water technically froze before the cold, but technically they appear to have froze almost at the same time.The temperature data loggers have a +/- of about 1.5 or 2 degrees (I don't have the specs at the moment).Ignoring the error in the data logger and other differences, it seems very little difference exists between freezing hot water versus cold water. Also, I'll add that both cookie tins had a high amount of ice indicating the temperature was truly 32 - and they were both ice at near the same time.Am I thinking of this wrong, or does the two technically freeze within a short time of each other and technically the hot beats cold but by a very irrelevant amount?

author: bdunham7
author_rank: Super Contributor
timestamp: February 18, 2022, 04:21:39 am
content: Did you weigh the water in each?

author: bostonman
author_rank: Super Contributor
timestamp: February 18, 2022, 04:24:18 am
content: Basically the same amount of water in each.Both tins were filled to the same height.

author: emece67
author_rank: Frequent Contributor
timestamp: February 18, 2022, 12:38:44 pm
content: .

author: strawberry
author_rank: Super Contributor
timestamp: February 18, 2022, 12:59:10 pm
content: http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/vappre.htmlwhat does F mean?

author: Zero999
author_rank: Super Contributor
timestamp: February 18, 2022, 01:02:03 pm
content: What were the weather conditions i.e. wind and cloud cover?If it's a clear night, the water will freeze quicker, than if it's cloudy, due to radiative cooling. The effective blackbody temperature of the sky is the more important than the air temperature. It's possible for the water to freeze, even if the air temperature is significantly above freezing.Wind should provide evaporative cooling, although it's often more associated with cloud cover and the water will get mixed up more so ice might be less likely to form on the surface.Temperature measurements don't always indicate the state of the water. It can be below 0°C, yet supercooled and still liquid.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 18, 2022, 01:44:53 pm
content: How long for the curves to drop below 32F?Tim

author: jpanhalt
author_rank: Super Contributor
timestamp: February 18, 2022, 02:36:39 pm
content: Quote from: bostonman on February 18, 2022, 04:24:18 amAs the poster #2 suggested, volume/mass changes with temperature. Start with the same mass in each tin. See:https://www.usgs.gov/special-topics/water-science-school/science/water-density

author: Siwastaja
author_rank: Super Contributor
timestamp: February 18, 2022, 03:26:31 pm
content: I don't understand this at all.1) Your graphs do not show the point where both have completely frozen, even at the point of temperature sensor; this would be seen as the temperature going BELOW 32F; significantly, of course, because of measuring inaccuracies.2) Your graphs however do show the point where the freezing, i.e., phase changestarts, at the sensor site at least, which is AT 32F. This is WAY sooner for the cold water, I don't get it where you get the idea that "hot water technically froze before the cold", since the graphs don't show anything else than starting of freezing, and it happens much earlier for the cold sample: already around 17:20; hot is there at around 18:10.The plot simply ends too early. Also having a few sensors per sample at different positions would be interesting.This is all as expected from common sense; of course the hot water takes longer, because it needs to cool down to the same temperature as the cold sample is already at, at which point the power dissipation should be exactly same.I'm aware of Mpemba's effect, but your measurement does not show it even if you expect it to. The harsh reality is, if this really was some "common knowledge" thing, it would be easy to recognize, not disputed, easy to replicate, and not named after a student making ice cream in 1960's. The Wikipedia page discusses this phenomenon quite well, so maybe you can try to find conditions recreating it because certainly the conditions need to be right. What you have now shows the complete opposite, and by large margin, so that I simply do not understand how you think by close zooming you can find it to prove your expectation.You are aware that tiny differences in sensors and water mineral content easily shift the measurement of 32F by easily 1F? Yet you expect that the 31.75F measurement means freezing is over? Even though the same zoom-in shows it bounces back to tad over 32.0F? This is just sensor noise.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 18, 2022, 07:20:49 pm
content: It is essential that you have convection cooling and not just radiative cooling, because an important part of the phenomenon israpidcooling. You should also use distilled water, because boiling water in a metal container (kettle) can easily add to the mineral content, and any suspended particles can act like freezing kernels, throwing everything off. Just add a bit of salt or sugar to the water, to see how drastically the results change. Drinking water always contains quite a lot of minerals.The Journal of Physical Chemistry published an interesting paper in 2015 by Jin and Goddard,Mechanisms Underlying the Mpemba Effect in Water from Molecular Dynamics Simulations. The "force fields" mentioned in the paper are interaction models based on theoretical models with numerical values fitted to reproduce known observables (heat capacity and so on) for water; I believe even non-chemists/physicists can read it (and ignore any technical details) to get a grasp on what actually is involved here.Kinetic energy in the form of heat is 'stored' in multiple degrees of freedom within a molecule. Essentially, the atoms in the molecule vibrate in various ways as temperature increases – that (and of course the overall kinetic energy of the molecule) is where the energy in the form of heat is –, and more recently,ab initiosimulations indicate that as water molecules are hotter, the length of the oxygen-hydrogen bond increases/weakens. When rapidly cooled, the bond length shortens slower than some of the other degrees of freedom (angular vibrations at the same distance), and to put it simply, very recently hot water seems to have lower heat capacity. (It is actually a bit more complicated than that, because it involves how these molecules interact with each other, and not just individual water molecules.) It is not any kind of "memory", it is just another facet of the phenomena we rely with metals:annealing. Water just happens to be an interestingly complex substance, where this kind of an effect occurs even in the liquid phase, not just in the solid phase. Overall, water is definitely one of the most difficult to simulate (outsideab initioAKA quantum mechanical modeling of the interacting electrons), which also shows in how in the above paper they used multiple unrelated models to confirm their results.

author: SL4P
author_rank: Super Contributor
timestamp: February 18, 2022, 09:42:12 pm
content: I remember this experiment from year 8 in school.The significant factor is the ‘rate of change’, not the immediate temperature of the samples.

author: tunk
author_rank: Super Contributor
timestamp: February 18, 2022, 10:14:40 pm
content: Were they both fully frozen when you stopped the test?If they were, I would have expected a further drop down to ambient.And it may have been better to put the sensors centrally in the tin.

author: Rick Law
author_rank: Super Contributor
timestamp: February 18, 2022, 10:28:48 pm
content: TheCarl Sagan"standardard" : "Extraordinary Claims Require Extraordinary Evidence."This "Mpemba effect" is an extra-ordinary claim. It is trying to invalidate the "Intermediate Value Theorem" long established in mathematics.For "Mpemba effect" to be true, the hotter one must get pass the temperature of the cooler one without ever taking on the temperature value of the cooler one.I believe the "Mpemba effect" is a description ofpoor experimental techniques.Here is why:Mpemba's observation was in 1963 by: "beakers in the icebox of a domestic refrigerator on a sheet of polystyrene foam". A 1960 style refrigerator likely is fan-less inside and relies solely on convection to "spread the cold" within. The evaporator may be directly connected to the ice box or is the ice box itself. There is no way to ensure that the two beakers are under the exact same condition. Even with modern refrigerators with fan-forced air circulation, you cannot ensure the conditions for the exact same physical spot will have the exact same condition over time."Beakers in the icebox" implies they were done together. When you placed the two beakers in together, they cannot both be at the same spot. Two different spots will have two different conditions. Where is the inlet of the refrigerant (coolest)? What else may be inside the refrigerator affecting circulation(s)? Etc., etcLet say I infer wrong. May be the two beakers were at the same spot and test one after the other. Again, conditions will be different for the two of them because they were there at different time. Immediately, one can reason that with something hotter inside the refrigerator, the average temperature inside will be higher and the cooling motor must run more to force to cool the refrigerator's thermostat enough to shut down the motor. So the hotter beaker was cooled more than the other.For such " observation " to be useful, One must document in detail how the conditions for these beakers are controlled and how exact same-ness was attained. Otherwise, one may just beobserving the effect that cooling ability inside a refrigerator varies a lot, by time and by location.If one place a thermometer inside a fridge, one would be amazed at how much the temperature really varies by time and placement. I did, right after I replaced the defunct thermostats in my fridge to validate it works. I still have the two digital thermostat connected: one sensor inside the freezer compartment and one inside the fridge compartment wired to displays outside. So I have been observing the freezer/fridge temperature for 2-3 months now.Furthermore, even what "freezing" means is not even defined in reporting this "observation".This lack of definition is very sloppy!Does it mean reaching freezing temperature? Water at freezing temperature still need to loose more latent heat for phase change to complete there by turned solid. The best way to check for phase change is when the temperature momentarily stops changing. That "temporally constant temperature" tells the observer that phase change is occurring. Is that what he means by freezing? How is the phase change observed?Hence my opinion: Poor documentation, poor understanding of physics experimental techniques, and poor definition. Very sloppy indeed.Good initiative and good curiosity however.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 19, 2022, 12:04:03 am
content: Quote from: Rick Law on February 18, 2022, 10:28:48 pmNo;must pass the temperature of the cooler one while having smallerthermal capacitythan the originally cooler one.One of the experimental verification methods is to choose a temperature, say +27°C = 300 K. Put say 200g of pure water in a stoppered beaker in a temperature bath for say a half hour. In a column, boil pure water and have it run through a powerful cooling sleeve (a pipe inside a pipe, with the coolant running in the outer pipe), at such a flow rate that the output is very close to the target temperature, and measure the exact same amount into an identical beaker.At this point, you should have two beakers with the same amount of pure water at the same temperature; the only difference being that one has been at that temperature for some time, the other just flash-cooled from near boiling.Then, put the two into the same liquid nitrogen bath (-196°C = 77 K), and measure the temperature changes in the two.The current understanding is that indeed, one will cool faster than the other; and this is what the "Mpemba effect" actually refers to.For reasons why, see my earlier post. If you need clarifications, I'd be happy to elaborate; it is interesting but complicated, surprising but not that weird at the atomic level. It's like the fact that solid water is less dense than liquid water at +4°C = 278 K.

author: bostonman
author_rank: Super Contributor
timestamp: February 19, 2022, 03:13:15 pm
content: I need to read these replies deeper and check out the links, but wanted to expand on a few things.One person stated my graphs don't make any sense, others commented about wind, etc... I understand many factors play into temperature from the obvious differences to minute molecular physical changes. Was my experiment ideal? Absolutely not, but it was enough to get a visual on what happens. By the way, the temp loggers I used were: Elitech URC-4 Temperature Logger taken at the quickest polling rate of 10s.The reason the data got "cut off" was to bring the items inside because it was getting late. Both cookie tins were frozen and both meters showed 32 (or nearly 32). The experiment was to see which one froze quicker and since both were at "32", they both were full of ice, etc... I brought them inside.My experiment was to see which froze faster, but, due to too many anomalies, including the error from the meters, all I could do is see which reached "32" the quickest. From reading over the years, I expected to see a significant difference such as the cold water still being liquid and the hot water being ice.Also, maybe this was already confirmed or rejected (again, I need to read through the responses better), but my understanding is that the greater the temperature delta, the quicker something will change to become equal, but will slow as it reaches the other temperature of the other object. As an example, if I came in from a snow storm and removed my wet coat, it will try to reach room temp quickly in the beginning, but will slow the closer it gets closer to the ambient temp (and I think ideally it will never reach the "exact" room temperature due to what occurs at the molecular level).My graph shows this happened: the hot water cooled very quickly and slowed as it approached 32 while the cold water had a much slower decrease because it was closer to ambient. Again though, my experiment wasn't meant to be specific and exact, it was to see which cookie tin was still liquid after the other became ice.The more I thought about things, the more I realized, there is little difference between where the hot water temperature begins. If I heated the water to one degree F hotter than the "cold" water, it would still take just as long to freeze from that temperature as if it started at 200 degrees F and decreased to 1 degree F hotter than the cold water.My conclusion (excluding for a moment what happens at the molecular level): with a typical cold environment such as a freezer or a cold winter night, if I want to make ice quickly, starting with hot or cold water isn't going to make a significant difference as to when ice is achieved.My graphs show that (assuming the meters are 100% accurate) that the hot water dropped to 32 while the cold was 32.1, however, both were almost a chunk of ice. I'll read through all the replies, but wanted to clarify that I'm not taking my measurements as fact, but more of a rough visual and didn't exactly get the results I expected.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 19, 2022, 04:05:58 pm
content: Quote from: bostonman on February 19, 2022, 03:13:15 pmYour graphs are completely as expected and make perfect sense: it shows that the cold sample starts freezing significantly earlier than the hot sample. It's just that your trace ends at some pointduringfreezing. Neither sample is fully frozen at the end, because both end up at 32F plus minus tiny amount of noise.The only thing that did not make sense are yourcomments; it's like you are looking at something completely different than what you posted?Actually deciding when the freezing is complete is quite difficult. The ice does not conduct heat very well and convection stops, so once the water is partially frozen, you don't know how much of it is frozen. If the sensor is in the middle of the tin, chances are high a good indication of being totally frozen is temperature reading starting to drop again, significantly below 32F. This would overestimate the time, though, because heat transfer through the block of ice is slow. Do place the sensors consistently, in the exact same place, in the two tins to compensate for this.You can't visually see if a block of ice is fully frozen. Try to drill a hole in it and liquid water may spurt out from the middle. State change is difficult because it happens at constant temperature: you can't see from temperature measurement how much frozen it is. The only way you surely know is to place gazillion of sensors and verify all of them measure below 32F (significantly enough to account for noise and inaccuracies in sensors, and the freezing point itself).

author: rfeecs
author_rank: Frequent Contributor
timestamp: February 19, 2022, 08:30:51 pm
content: The article from the video:"Questioning the Mpemba effect: hot water does not cool more quickly than cold"https://www.nature.com/articles/srep37665Quote

author: Rick Law
author_rank: Super Contributor
timestamp: February 19, 2022, 08:53:58 pm
content: Quote from: bostonman on February 19, 2022, 03:13:15 pmre: "...maybe this was already confirmed or rejected...my understanding is that the greater the temperature delta, the quicker something will change..."Yup, confirmed by various replies by multiple people already.re: "...starting with hot or cold waterisn't going to make a significant differenceas to when ice is achieved..."That is the "latent" heat. The "latent heat of fusion" of water to ice (phase change) is much greater than heat capacitance of water.- It takes 1 calory to heat 1 gram of water by 1 degree C.- It takes 80 calories for 1 gram of water to phase-change between ice and water (latent heat of fusion).- It takes 540 calories for 1 gram of water to phase-change between steam and water (latent heat of evaporation).For 1 gram of water to phase-change between water and ice, it could change the temperature of water by 80 degrees C. That is why I was so critical of thelack of definition of "freezing"when "Mpemba's observation" was made -- it takes 80x the heat exchange of dropping 1 degree verse for it to fully freeze.When big things are wrong, the details hardly matter- this is the scale of worrying about minutes when hours are wrong.By the way, interesting to bring up one point here.Calories (with capital C used for food) is 1000x calories (lower case C used in Physics). Some "food science" people must have needed glasses when they first adopted the Physicist's unit of calories. Someone must have mixed upgandkgby mistake. So 1Cal heats 1kg of water 1 degree in food "science" whereas 1cal only heats 1 gram of water 1 degree. Your bottle of Coke at merely 240 Calories is really 240,000 calories! (No wonder I am getting fatter 1000x faster than I feel I should.)

author: Siwastaja
author_rank: Super Contributor
timestamp: February 20, 2022, 11:14:11 am
content: Just forget about calories. They have no place in science or engineering.

author: bostonman
author_rank: Super Contributor
timestamp: February 20, 2022, 05:11:06 pm
content: QuoteI read these messages more thoroughly than now that I had time to devote in front of the computer (sometimes I scan the messages on my phone while out so I have time to process what is being explained).I think the answer was provided by methods of more wording within explanations, but at least it confirms my initial understanding of the larger the temp delta: the greater the temp delta the quicker it changes and slows as it gets closer to the other object (room temperature in this case as per my previous example).Maybe for a moment we should forget about actual freezing because the physics behind ice is more complex than I thought. I'll openly admit, I wanted to keep the data going for much longer than what my graph shows. Once I saw the outside temp was about 25 degrees F and expected to drop, I realized this could be my one last opportunity before winter passes to conduct this test, however, I expected the water to freeze much quicker. Due to thinking it would freeze quicker, I set up my area in an inconvenient location and in open view mid-afternoon. Once it turned night, I feared if I kept things setup throughout the night, animals might disturb things and/or someone may see the setup and enjoy two free saw horses (not that I live in a bad area, but someone did steal my garden hose and reel one year).In any case, I made the assumption that seeing "ice", and 32 degrees F on the meters, was enough data to conclude what happened. Everyone is correct and that the tins weren't a solid chunk of ice (but they were quite solid), but my conclusion at a gross level was: hot water and cold water both reached "32" at nearly the same point (again, let's forget about actual freezing for a moment).The other portion of my conclusion: If I had friends coming over and was out of ice cubes for drinks, starting off with hot water isn't going to provide ice cubes significantly quicker than plan old cold (tap) water. What I also knew before the experiment: if I place hot water in my freezer, I'm going to heat the freezer thus making the freezer work harder. Obviously this is why I conducted my experiment outside as one tin of hot water isn't' going to rob the Earth of cold.Another reason I removed the test rather than keep it into the night: I knew many portions of my setup weren't ideal. As someone pointed out, multiple temperature probes placed in various areas would be ideal and all probes in the same locations in both tins; but also, the plywood the tins sat on were a heat sink, the data loggers aren't perfect, etc...I expected to see a significant difference in temperature once one of the tins got close to 32, maybe something like the cold was 38 and the hot was 32 and it was clear hot or cold "freezes" faster than the other. Once I saw both tins had a significant amount of ice and it seemed both tins got there at nearly the same time, I figured at a gross level, I concluded hot versus cold have little affect on how long it takes to freeze.Maybe my statement of using "freezing" was overboard. At a common sense level, I realize water doesn't always freeze as expected and at exactly 32. Now that I've read some technical reasons, I have a better understanding why. Having said this, it was probably wrong to to use absolute statements like "froze".Based on my graph, and leaving out that my tins weren't technically "ice", I feel both reached an end point nearly the same time. Now at an atomic and physics level, and water impurities, I can't make any serious conclusions on which actually froze (and froze solid) quicker.This experiment is from something that occurred years ago. My friend needed ice cubes and used hot water telling me hot water freezes faster. Over the years I've kept wanting to conduct such an experiment.I think it's safe to say, if I have a friend that tells me using hot (tap) water is going to provide ice cubes much quicker, I know this will not be the case.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 20, 2022, 05:18:41 pm
content: Quote from: bostonman on February 20, 2022, 05:11:06 pmBut this is what I really struggled to understand. Like, are we looking at the same graphs? Because the graph you posted shows the cold one reached 32F at 17:15, and the hot sample at 18:15, roughly. Seems a big difference to me!

author: bostonman
author_rank: Super Contributor
timestamp: February 20, 2022, 05:37:30 pm
content: Oh, I understand your statement now.You're correct, the cold water is 32 F sooner than the hot. I still feel due to many factors, it's close enough to conclude at a gross level you can't gain freezing time from starting off hot or cold.But yes, you are absolutely correct, the hot water was still hotter than the cold and therefore took longer to "freeze"; clearly an error on my verbal statements versus the graph.edit: I attached an expanded section of the graph

author: Siwastaja
author_rank: Super Contributor
timestamp: February 20, 2022, 06:23:19 pm
content: It could even be that the hot sample starts freezing as late as 19:10 or so, it's hard to say!Mentally shift the red graph up by 0.25F (assuming sensor offset error, or small differences in mineral content) and you see what I mean: doesn't it replicate what the cold sample did earlier, even including that interesting "overshoot" which bumps back up again? (Someone more familiar with small-scale effects not well explained by the simple equations could comment whether those overshoots and bouncebacks are actual, or measurement artifacts.)

author: BeBuLamar
author_rank: Super Contributor
timestamp: February 20, 2022, 11:47:06 pm
content: Assuming the outside temperature is constant. The initial cooling rate of the hot water is faster but it's hotter so it has to cool down to the same temperature as the cool water at which time the rate of cooling is the same as the cool water when it started but now the cool water is cooler. So no you do not see the hot water reaches the outside temp before the cool water.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 21, 2022, 12:06:53 am
content: 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 occurin these conditions) illogically into "the effect does not exist".At the core of the real Mpemba effect is thatheat capacityis not constantin 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 leastnineteen 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, likewater 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 heatedrapidly.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 localizedheatingcan 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 thatat the same temperature, the energy flow from the recently-hot sample to the heat bath ishigherthan 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. Nothinganomalousin 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 inab initiosimulations, 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.)

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 21, 2022, 12:26:51 am
content: 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 21, 2022, 12:53:56 am
content: Quote from: CatalinaWOW on February 21, 2022, 12:26:51 amNot 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 ofanomaliesorstrange phenomenaas used in e.g. History channel TV shows.Quote from: CatalinaWOW on February 21, 2022, 12:26:51 amFunnily enough, the only requirement for that to happen is that the water does not containseed 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, 10-15seconds 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.)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 21, 2022, 02:40:55 am
content: 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.Tim

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 21, 2022, 03:04:30 am
content: 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.

author: IanB
author_rank: Super Contributor
timestamp: February 21, 2022, 03:28:01 am
content: Quote from: Nominal Animal on February 21, 2022, 12:06:53 amWhat do you mean by "equilibrium state"? Thermal equilibrium? Mechanical equilibrium? Chemical equilibrium?Furthermore, heat capacityis 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 21, 2022, 05:03:27 am
content: Quote from: T3sl4co1l on February 21, 2022, 02:40:55 amNot 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 asVan 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 differentdegrees 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.Quote from: T3sl4co1l on February 21, 2022, 02:40:55 amAnyone 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,everyexperienced 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.Quote from: IanB on February 21, 2022, 03:28:01 amThermal 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.Quote from: IanB on February 21, 2022, 03:28:01 amThat 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 becometemporarilycooler 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.

author: IanB
author_rank: Super Contributor
timestamp: February 21, 2022, 08:40:32 am
content: Quote from: Nominal Animal on February 21, 2022, 05:03:27 amSorry, 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.QuoteI sincerely doubt that such peer reviewed articles appear in mainstream physics journals, or if they do, you are misinterpreting what they are saying.QuoteThe 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 21, 2022, 10:28:55 am
content: I'm trying to explain things in a way that laymen understand it. Feel free to nitpick.Quote from: IanB on February 21, 2022, 08:40:32 amIf 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.

author: magic
author_rank: Super Contributor
timestamp: February 21, 2022, 10:51:13 am
content: Quote from: Nominal Animal on February 21, 2022, 12:06:53 amThat 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 21, 2022, 01:49:14 pm
content: Quote from: magic on February 21, 2022, 10:51:13 amThen read the linked paper.

author: magic
author_rank: Super Contributor
timestamp: February 21, 2022, 04:01:19 pm
content: 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 21, 2022, 06:44:46 pm
content: Quote from: magic on February 21, 2022, 04:01:19 pmSigh.Here's a snippet from the abstract of the Zhang et al. paper:QuoteNote the part where it mentions "Cooling  energy, [...] at a rate of history dependence"?The skin supersolidity is a related phenomenon discussed for the last decade or so, starting atSun, 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.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 21, 2022, 06:49:16 pm
content: Quote from: magic on February 21, 2022, 10:51:13 amThe 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.

author: m k
author_rank: Super Contributor
timestamp: February 22, 2022, 11:41:09 am
content: 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 23, 2022, 01:23:11 am
content: I completely forgot, and I've actually done it in real life!Here is Viva Frei doing it on Youtube:

author: IanB
author_rank: Super Contributor
timestamp: February 23, 2022, 01:59:05 am
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: February 23, 2022, 02:23:37 am
content: Quote from: IanB on February 23, 2022, 01:59:05 amThis is why snow machines use hot water...oh, wait...

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 23, 2022, 03:59:08 am
content: Quote from: IanB on February 23, 2022, 01:59:05 amNeither 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.Quote from: bdunham7 on February 23, 2022, 02:23:37 amHa, 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 suchclaimsbeliefs. 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, butreligion? Dammit, I'm out.

author: TMM
author_rank: Frequent Contributor
timestamp: February 23, 2022, 04:05:01 am
content: 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...

author: IanB
author_rank: Super Contributor
timestamp: February 23, 2022, 04:30:50 am
content: Quote from: Nominal Animal on February 23, 2022, 03:59:08 amI'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 effectmightbe observed. This is not evidence, it is speculation.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 23, 2022, 04:50:07 am
content: Quote from: IanB on February 23, 2022, 04:30:50 amPoint a single one, and stop bullshitting by making unfounded claims, and we can have anusefulconversation.What you have been posting, isn't science: it is assertion of unfounded beliefs.

author: IanB
author_rank: Super Contributor
timestamp: February 23, 2022, 05:09:14 am
content: Quotehttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC5121640/#:~:text=We%20conclude%2C%20somewhat%20sadly%2C%20that%20there%20is%20no%20evidence%20to%20support%20meaningful%20observations%20of%20the%20Mpemba%20effect.

author: bdunham7
author_rank: Super Contributor
timestamp: February 23, 2022, 05:14:19 am
content: Quote from: Nominal Animal on February 23, 2022, 03:59:08 amI'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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 23, 2022, 05:23:04 am
content: Quote from: bdunham7 on February 23, 2022, 05:14:19 amFine. 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.

author: Nominal Animal
author_rank: Super Contributor
timestamp: February 23, 2022, 05:38:42 am
content: Quote from: IanB on February 23, 2022, 05:09:14 amDid you read the article? The experiment was done by a single person, Henry C. Burridge, who furthermore redefined the effect:QuoteThere 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 ––whenandin which materialsdoes the Mpemba effect occur –– has been sufficiently proven in my opinion, and arguments that are based onredefining the word to mean some other phenomenonare utter bullshit not worth discussing.

author: magic
author_rank: Super Contributor
timestamp: February 23, 2022, 08:25:54 am
content: Quote from: Nominal Animal on February 23, 2022, 05:38:42 amThat'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

author: magic
author_rank: Super Contributor
timestamp: February 23, 2022, 08:32:15 am
content: 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 termsMy 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 forequalenergy 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

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 23, 2022, 09:05:50 am
content: Quote from: TMM on February 23, 2022, 04:05:01 amThat's...exactly what he said though. o.oSo, 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, becausethe 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.QuoteDoesn'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 amIt 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  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

author: m k
author_rank: Super Contributor
timestamp: February 23, 2022, 11:00:05 am
content: Quote from: magic on February 23, 2022, 08:25:54 amThere 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.

author: bdunham7
author_rank: Super Contributor
timestamp: February 23, 2022, 02:56:42 pm
content: Quote from: T3sl4co1l on February 23, 2022, 09:05:50 amEither the low heat capacity condition related to the O-H bond length would have to both survive the phase change and then relax slowly enough that the heat could be dissipated to the environment without any meltingorthere would have to be an alternative form of ice, like Ice-9. Or something I haven't thought of.QuoteThe main issue I have with the theory is with applying the claim broadly without any broader experimental evidence. I also have an issue with the conflation of skepticism with stupidity, but that's another matter.A very simple possible explanation of Mpemba is available based on supercooling. If you supercool water, it may not always freeze quickly once it starts simply because the crystallization releases heat to the remaining liquid and additional heat rejection is required. If your freezer isn't very cold--say -10C--and you have a sample of water that will supercool to -5C before freezing starts, then the latent heat of fusion will be transferred slowly, proportional to the 5C difference. If you also have another sample of water that is crystallizing at 0C, then that system will be transferring the heat twice as fast based on the 10C difference. So all you need is a mechanism by which one sample is susceptible to supercooling and the other is not, the right ambient temperature and some luck. This would explain why the legend exists, but the phenomenon is not reliably observed experimentally, at least not in the ice-cube tray model. This is why I suggested that any experimental measurement should be continued until equilibrium is reached and certainly not stopped at 0C.

author: IanB
author_rank: Super Contributor
timestamp: February 23, 2022, 03:34:16 pm
content: Quote from: T3sl4co1l on February 23, 2022, 09:05:50 amActually, no. What it needs is an experimental procedure, clearly and precisely defined, so that any worker in any laboratory can reproduce the effect consistently.So far, this does not appear to have been done. Where experimenters have claimed this effect, others have not been able to reproduce the same numbers.Until there is a real, reproducible, observable phenomenon it is right to remain skeptical.Computer simulations and theoretical models explaining how such a phenomenon might happen are interesting on an intellectual level, but they all remain hypothetical until they are able to give a precise specification for an experiment that will demonstrate in practice what the equations predict.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 23, 2022, 06:00:17 pm
content: Actually, no -- it needs both! An experiment is fine, but teasing out conflating variables can be tricky. It's one thing to point at an experiment doing the thing and say "ha, see?", but conclusive proof requires both angles.For example, point x-rays at it -- if it's bond lengths, then the diffraction pattern sure as hell ought to change. It'll change anyway due to temperature (I would think?), but there should be an aberration in the distribution if it really is energy stored in bond lengths.Or also, would that change density somewhat? Enough to measure? It's effectively a metastable phase of liquid water, that must count for something?Another example of experimental ambiguity is just saying "oh, it freezes faster". Well, what, it reaches 0C faster? Or it drops below 0C (fully solid phase) faster?Quote from: bdunham7 on February 23, 2022, 02:56:42 pm...As exemplified here.Which is something else XRD would show, phase fractions. With the ice phase giving sharply defined rings or whatever.If the toss-a-pot-of-hot-water-on-a-cold-day trick is indeed an example of this effect, then it would seem the former is relevant -- given that the "control" doesn't freeze much or at all!Of course you have to be careful that the ionization doesn't also cause nucleation, where supercooling might be involved. But it would be nice to show it's not a supercooling phenomenon but something different entirely.Sort of related:https://arxiv.org/ftp/arxiv/papers/1107/1107.4795.pdfAnd, any other low-impact analyses would be effective, too; maybe Raman something or other, would be more "hands free" than ionizing radiation? Or, there's a zillion other probing methods I don't even know about, probably some neat things to try among them...Tim

author: IanB
author_rank: Super Contributor
timestamp: February 23, 2022, 06:53:58 pm
content: Quote from: T3sl4co1l on February 23, 2022, 06:00:17 pmWhy would you say conclusive proof requires an explanation of a mechanism? For much of history, people knew that certain things happened, but they didn't know why. For instance, everyone knew for millennia that if you seared meat it got a brown color with a pleasing flavor. The mechanism for why it happened was not known, but the observation was nevertheless an incontrovertible fact. Only later was it discovered that it is due to a chemical reaction between amino acids and reducing sugars, and today we can call it the Maillard reaction.Turn it around, and consider general relativity. Einstein made predictions based on a mathematical model, but those predictions were only a hypothesis until confirmed by observation. Without the real world observations, general relativity would remain an intellectual curiosity, rather than a testable theory.The Mpemba effect can only happen if water or another substance exhibits thermal hysteresis. You can come up with a theoretical mechanism to produce such hysteresis, but then it should be possible to construct an experiment with the right elements to observe the effect in reality (as can be done with magnetic hysteresis). Without such experiments the effect is only "real" in the mathematical, theoretical sense. It is not real in the observational, experimental sense.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 23, 2022, 07:18:10 pm
content: Yes, exactly -- I mean as a well proven, understood, scientific theory. As opposed to a phenomenon (observation lacking explanation), or hypothesis (explanation lacking observation).Tim

author: Siwastaja
author_rank: Super Contributor
timestamp: February 23, 2022, 07:33:36 pm
content: Quote from: IanB on February 23, 2022, 06:53:58 pmIt isabsolutely nececessaryto rule out coincidental unexpected correlations; if you have just measurement results and no explanation for them, you are not proving any theory, just replicating the experiment and it's well possible it demonstrates something completely different yet you have no idea.I think it's quite revealing you don't understand such basic requirement of scientific research.So yes, you need both. Only then it is valid science.

author: bdunham7
author_rank: Super Contributor
timestamp: February 23, 2022, 07:56:59 pm
content: Quote from: Siwastaja on February 23, 2022, 07:33:36 pmThe causation/correlation issue only arises when you don't directly control the causation part. If I take 1000 cuts of meat from 100 different animals and hang them over fire by a stick, I can safely conclude that the fire causes them to cook without understanding how or why. It's true that not understanding 'why' might cause a mistaken conclusion to be made that does not allow me to predict the result in a slightly different experiment-- for example is the cooking due to the heat or the light? I take the philosophical position that we never actually completely know "why" or "how" anything happens, we just have models that are good enough to allow us to make predictions with a certain amount of reliability.If I can control various aspects of water in an experiment--how it is heated/cooled/handled and so forth, I can see if and when the Mpemba effect occurs and then make a catalogue of the various conditions where it does and doesn't seem to manifest itself, such as the water sample temperatures, the container characteristics, the freezer temperature, etc etc. This catalogue might show me, for example, that the Mpemba effect is observed as long as the hot water is at least 80C, the container is metal but not wood or clay and only if the freezer temperature is between -5 and -15C. That list of conditions where the effect does and does not occur would constitute scientific knowledge without ANY model or knowledge of the underlying processes, or even the atomic or molecular nature of water itself. This is how science worked for thousands of years--there weren't many models and they were all completely wrong anyhow for the most part, except perhaps for simple mechanical devices. Nowadays some think we have all that figured out, but I'm not so sure.

author: IanB
author_rank: Super Contributor
timestamp: February 23, 2022, 08:15:38 pm
content: Quote from: Siwastaja on February 23, 2022, 07:33:36 pmI think you are introducing something new here (the need for a scientific theory) that is not part of the original question. The question at hand is: "Can such an effect be observed by anyone, anywhere, in a reproducible manner?" In other words, is there even a phenomenon that needs explanation?In this case I contend that no such phenomenon has been conclusively demonstrated in a laboratory, so there is not even a reason to seek a mechanism.On the other hand, if someone hypothesizes a mechanism, then it should be testable by experiment. But I contend there is no more than anecdotal evidence or hearsay at the moment, with no reproducible, experimental procedure to demonstrate it.Surely, if there was an experimental procedure that reliably produced the effect, then it would be documented somewhere? You or I could read the experimental method, and given an adequate laboratory we could reproduce it for ourselves. It would be in high-school science classes. There would be YouTube videos by the likes of NileRed or Veritasium showing it. Where are they?

author: PlainName
author_rank: Super Contributor
timestamp: February 25, 2022, 12:48:26 am
content: QuoteIt's useful to remind us of the original proposition, but then why do you arbitrarily say:QuoteWhy -20? Isn't the question merely which freezes faster? Otherwise you could pick -127C, and microwaved super-heated water to start, and all of a sudden the conditions for your 'ultimate question' are just as much rubbish as you complain his (alleged!) edge cases are.

author: bdunham7
author_rank: Super Contributor
timestamp: February 25, 2022, 02:24:17 am
content: Quote from: dunkemhigh on February 25, 2022, 12:48:26 amBecause that is approximately how cold my freezer is?You can pick any numbers you like, and as I said elsewhere, it would be appropriate to try different combinations. But -20C isn't what is important, it is the entire dataset as the cooling and freezing occurs, time and temperature. The point is simply that you need to observe that long enough and far enough down that you can be sure that the phase change is complete. Then you can go back and look at the data to see when you deem the sample 'frozen'. If that point is clear and indisputable, great. If not, you have more questions.

author: PlainName
author_rank: Super Contributor
timestamp: February 25, 2022, 12:58:49 pm
content: QuoteBut in doing that you are merely picking some semi-random point at which you say "should be done now". The samples could have been completely frozen much earlier, or even later, and you won't know exactly when, but your confirmation bias will ensure the result you seek is apparent.And in the end you won't be able to say why the repeatable effect shouldn't happen, only that it hasn't for your crude and unrepeatable experiment. OTOH, NA has quoted sources that, if the effect is real, can explain precisely how it can be real.

author: bdunham7
author_rank: Super Contributor
timestamp: February 25, 2022, 02:46:19 pm
content: Quote from: dunkemhigh on February 25, 2022, 12:58:49 pmWhat do you mean by 'semi-random point'? I think that most would agree that the completion of the phase change would be indicated by the temperature starting to fall again after a plateau. How would you determine at what point the samples are indeed 'frozen'?

author: PlainName
author_rank: Super Contributor
timestamp: February 25, 2022, 04:25:06 pm
content: QuoteIt's not completely random since it's limited to domestic refrigerator capabilities. Water freezes at 0C, so why not pick that? OTOH, if there are impurities then it will be a bit different, so how are you going to cope with unknown quantities of those?Further, the lower ambient temperature would reduce the time available to observe the effects (and increase the likelihood of partial freezing). Shove the ice cube tray in liquid nitrogen and you'd be hard pressed to tall the exact time to the ms when it all froze. Use ambient of -5C and you have much much longer to determine things (and you won't have a crusty shell and fluid interior).So, why -20C. No real reason other than that's what your freezer is set to. It's a semi-random figure.

author: bdunham7
author_rank: Super Contributor
timestamp: February 25, 2022, 05:31:03 pm
content: Quote from: dunkemhigh on February 25, 2022, 04:25:06 pmDo you mean use an ambient (freezer) temp of 0C or terminate the experiment at 0C? Either way, how can you determine that freezing has occurred?QuoteI haven't proposed that -20C is the correct or only temperature to use. In fact I proposed a possible mechanism by which the Mpemba effect might be observed some times and not others and also that experiments with varying freezer temps might reveal that. Did you read that? However, -20C, in addition to being approximately what my freezer is set to, is also cold enough that supercooling is unlikely and you can be fairly sure that the water is completely frozen if you allow it to come near equilibrium. So if I were going to conduct a set of experiments, in the first round at least I would use -20C as my coldest test and then successively warmer temps up to near 0C. Unfortunately, both my freezers have a lot of food in them so I won't be doing this anytime soon.QuoteIn that case it might actually not turn into conventional ice. Ice-9 is fiction, but there is another amorphous state that occurs when you cool water so fast the the ice crystals don't have time to form before things stop moving.

author: PlainName
author_rank: Super Contributor
timestamp: February 25, 2022, 06:42:07 pm
content: QuoteTerminate.QuoteWell, presactly. That's the problem, isn't it? And you not only have to determine that freezing has occurred, butwhenit occurred.QuoteIt was implied when you said: "but the ultimate question for me is whether I should use hot or cold water in my ice cube tray."

author: bdunham7
author_rank: Super Contributor
timestamp: February 25, 2022, 06:50:11 pm
content: Quote from: dunkemhigh on February 25, 2022, 06:42:07 pmThat is a problem with a pretty well established and accepted solution. Freezing is complete when the temperature starts dropping again at the end of the plateau. If that is a sharp curve, you know the point fairly precisely from graph of your data points. But if you terminate the experiment at 0C, you can't possibly pinpoint the time when the water is completely frozen, at least not with a graph of temperature.

author: PlainName
author_rank: Super Contributor
timestamp: February 25, 2022, 08:08:37 pm
content: QuoteWhen your temperature probe drops you know the entire volume is frozen? Not just the part that your probe is embedded in?

author: IanB
author_rank: Super Contributor
timestamp: February 25, 2022, 09:04:19 pm
content: From an experimental point of view it is important that the sample is in a completely uniform state at the beginning and end of the experiment, so that its internal properties are everywhere the same. A practical way to achieve this is to have the sample well mixed. If you allow the sample to freeze, it becomes impossible to have it well mixed, and therefore impossible to know when it is uniformly frozen. For this reason, experiments should not allow the sample to freeze. They should go from liquid at one temperature to liquid at another temperature.

author: PlainName
author_rank: Super Contributor
timestamp: February 25, 2022, 09:29:34 pm
content: QuoteI know what you're saying. Just thought it was funny, given the context

author: bdunham7
author_rank: Super Contributor
timestamp: February 25, 2022, 09:30:36 pm
content: Quote from: dunkemhigh on February 25, 2022, 08:08:37 pmThat's an issue for some experimental finesse and probe placement, but the general theory is that the temperature remains constant until the whole thing is frozen because any remaining liquid is still rejecting heat as it freezes. OF course any real physical sample will have a gradient, but nobody said experimental physics was easy, even for simple things. But this is not some new thing I'm proposing....

author: bdunham7
author_rank: Super Contributor
timestamp: February 25, 2022, 09:33:51 pm
content: Quote from: IanB on February 25, 2022, 09:04:19 pmThat depends on what the purpose of your experiment is. If you are testing the theory that one sample has a persistently different heat capacity than another, then OK. Otherwise, and in the context of the OP's post and so on, that's probably not too enlightening.