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| High standards, low expectations  |
Depends on how hot. If the water is hot enough, a significant portion may evaporate in your freezer, leaving a smaller mass left over to freeze. This smaller amount of water will then need to give off significantly less overall heat than the cool tray of cubes, and potentially freeze “faster”. The reward for hard work, is more hard work arcwelder76, 2013 | |||
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Almost as Fast as a Speeding Bullet |
From what I read, that is one of the biggest problems with it. People have observed it, but it is not consistently reproducible. ______________________________________________ Aeronautics confers beauty and grandeur, combining art and science for those who devote themselves to it. . . . The aeronaut, free in space, sailing in the infinite, loses himself in the immense undulations of nature. He climbs, he rises, he soars, he reigns, he hurtles the proud vault of the azure sky. — Georges Besançon | |||
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| Member |
Nothing whatsoever to do with contrail formation. Turbojet engine exhaust is hot; combustion of kerosine in a jet engine produces water vapor, and water vapor freezes. The fact that the exhaust is hot does not cause nor increase the formation of a contrail. The formation of a contrail is entirely due to water vapor presence, condensation nuclei in the jet exhaust, and environmental atmospheric conditions at the point of formation. It's not the heating of the exhaust that causes the contrail, which will form only when conditions are correct; one can see it form and fail to form as the aircraft passes through air which is conducive, and not conducive, to contrail formation. Moreover, one also sees distrails, which which cloud surrounding the exhaust effluence is dissipated, rather than a contrail forming. It can go either way, depending on conditions. What is not a part of the process is hot exhaust causing water to freeze; the only contribution of that hot exhaust in a contrail is an after effect of combustion and the production of adequate water vapor. The water doesn't freeze because it got hot. As for supercooled water droplets not freezing, and that being a component of like samples in a freezer, not. A glass or beaker of water in a freezer doesn't become supercooled and fail to freeze when a hot cup of water does freeze. Warm or hot water does not freeze first, and certainly not because of "supercooling" of a water sample in a fridge. Supercooling of water, which is the cooling of water to a temperature below freezing while still in the liquid state, occurs in nature down to -40 deg C/F, but only in small droplets, and only due to surface tension on the droplet. It's supercooled water droplets that can lead to a rapid buildup of ice in flight as the aircraft breaks surface tension and the water freezes instantly, and also what we see in freezing rain. This does not occur in a test sample in a freezer, and won't occur when a warm and cold water sample is subjected to identical conditions in the freezer. Water has a given specific heat capacity of 4.184, and a change in water temperature is a function of heat added or removed. Unless the specific heat capacity of water is altered by changing the chemical composition of the water, then the cold water will freeze first. Simple chemistry and physics. Heating the water doesn't change the specific heat capacity, and mathematically the warm water sample in the freezer has a greater temperature differential to accomplish, and a longer time will be required to do it. | |||
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Don't Panic |
There's a reason why science is more than just anecdotes. We are getting fairly close to that worst-of-seasons which will provide the doubters a chance to do their own experiments, rather than relying on possibly-fake science persuasively laid out on websites. Once it gets below freezing, get two large containers, and put an equal amount of water into both. Put one in the refrigerator, and leave the other at room temperature. After a day, put them both out into the cold where you can see them from inside, and watch. (or put your camera on time-lapse.) I could tell you what you'll observe, but I'm just this guy, you know.  The key things are: 1) identical containers 2) identical amount of water 3) identical motion (kinetic energy in the water) - in this case, zero 4) identical composition of the water (no difference in ions, etc.) | |||
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| Help! Help! I'm being repressed!  |
In certain circumstances. | |||
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| Member |
This is one of the better explanations I have seen- The end describes the molecule "memory" that would have to exist if mpemba is true. If there is accelerated cooling based on previous temperature, then how does the water know what temperature it had when to use. Link to original video: https://www.youtube.com/watch?v=SkH2iX0rx8U | |||
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Baroque Bloke |
I don't believe that hot water freezes faster than cold. Nor do I believe that the earth is flat. Serious about crackers | |||
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Member |
People believe what they want to believe. Year V | |||
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| Nature is full of magnificent creatures |
It is interesting to watch water boil at room temperature. Physical chemistry is fascinating! | |||
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A Grateful American |
I was referring to adiabatic cooling, and as there certainly are components to the atmosphere that are both conducive and unfavorable, the rapid expansion of compressed hot gases are what bring about contrails. Water vapor not compressed would boil off at that altitude, but unlikely create anything the size of contrails because of the rapid expansion and energy of the other gases and air exiting the nozzle when heated. "the meaning of life, is to give life meaning" ✡ Ani Yehudi אני יהודי Le'olam lo shuv לעולם לא שוב! | |||
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| Little ray of sunshine  |
No. A PhD chemist and college professor once confessed he had heard the "hot freezes faster" thing, and about half believed it. Then he thought about the laws of physics and realized it is pure nonsense. The fish is mute, expressionless. The fish doesn't think because the fish knows everything. | |||
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| Member |
The Mpemba effect is well known, but almost always counteracted by the Crompoopoo Effect in practical situations. "Crom is strong! If I die, I have to go before him, and he will ask me, 'What is the riddle of steel?' If I don't know it, he will cast me out of Valhalla and laugh at me." | |||
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Frangas non Flectes |
I've also heard that cold tap water run into a pot will boil faster than a pot filled with hot tap water. My observations have been the opposite, but I'm not a physicist. ______________________________________________ Carthago delenda est | |||
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One observation, when the Zamboni resurfaces the ice between periods of a hockey game it lays down hot water, just sayin' | |||
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| Member |
Rapid expansion is not causing freezing of exhaust gasses. -54 degree temperatures at altitude are causing the freezing. | |||
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| Member |
Cold water on snow makes slush, frozen slush sucks to skate on, hot water melts snow, fills deeper ruts in the ice, so it can freeze nice and smooth. Smooth ice good, bumpy ice bad. | |||
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| A Grateful American |
I did not say the rapid expansion caused the freezing. I said the rapid expansion of heated gases and the contained water resulted in the contrails, vs none expanding water. Both will freeze, but the expanding contributes to this. If you streamed quantity of water in a non-compressed liquid phase from an orifice and the same amount in gaseous phase that exits from the engine the contrail is going to be the faster freezing, from the expansion and liberation of heat to the colder air, than the stream. The stream will also "boil off" but without the heat, it will do so much more slowly. The comparison of that effect to the tossing of boiling water, which "expands/spreads out and the energy from the heated water is rapidly cooled by the vapor/steam being exposed to more "surface" to cold air. A tub of boiling water will need to transfer all of it's heat to the air in order to be lowered to freezing point. Boiling water dispersed will be rapidly turned into steam, as it is at boiling point when it expands by the act of throwing it and it is no longer in a total liquid phase, but a partial (small droplet) vapor phase. The "spreading" is expansion and there is a small transfer of energy, and the surface area of the water and the cold air are increased dramatically, and the water freezes, leaving a cloud of ice crystals. The gases of jet exhaust do this as well, (and to a greater degree than tossing boiling water), and pressure change upon exit of the nozzle has the effect of cooling the water in the gases rapidly. "the meaning of life, is to give life meaning" ✡ Ani Yehudi אני יהודי Le'olam lo shuv לעולם לא שוב! | |||
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paradox in a box |
The reason for this is that the hot water melts a bit of the ice and makes the new ice bonded with the old, rather than having a sheet that will chip off. As far as pipes freezing, I'm wondering if maybe just the hot water pipes burst while the cold don't. It may have something to do with how the crystals form and the expansion of the water when it crystallizes rather than the speed at which they freeze. But I'm not a physicist. I do have a solution though to ease everyone's mind. If you keep 2 ice cube trays, then as one is empty you fill it (with hot or cold), then start using the other ice cube tray, none of this will matter. (Add more trays if you drink a lot) These go to eleven. | |||
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| Eating elephants one bite at a time  |
Bah yer both full of it. There ain't no such thing as contrails. Everyone knows thems chemtrails what come out of the back of jets. It's the government spreading stuff to make us all obey without question.     | |||
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Ammoholic |
Super heated water, can get over 212*, but you must use pure water, won't happen with tap water. Jesse Sic Semper Tyrannis | |||
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