Mpemba effect: warmer water can freeze faster than colder water(en.wikipedia.org)
en.wikipedia.org
Mpemba effect: warmer water can freeze faster than colder water
https://en.wikipedia.org/wiki/Mpemba_effect
14 comments
Or, perhaps even more well known to Canadians, Zambonis use hot water to resurface rinks.
Also,the "hot water pipe freezes first" is a popular "myth" (turns out it may be true). This has happened to me and the plumber seemed to take that for a fact despite not having a reasonable explanation.
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> using boiling water in snow-making machines
The seems like a related effect: https://www.youtube.com/watch?v=IQ3kQPWlU-o
So evaporating water cools the surrounding air?
The seems like a related effect: https://www.youtube.com/watch?v=IQ3kQPWlU-o
So evaporating water cools the surrounding air?
Yes. To transition from liquid to gas the water must absorb heat. That heat must come from the air, cooling it.
Does the same effect happen with 100% relative humidity?
I've always disliked the explanations I've seen for the Mpemba effect. They seem to be based on poorly defined terms, odd assumptions, and uncontrolled variables. The (poorly) linked 2010 paper by Brownridge is the first description that I'm inclined to trust: https://www.binghamton.edu/physics/docs/Preprint%20and%20Sup...
Impressively, he describes a controlled duplicable setup in which he's able to reliably freeze (using an exact definition) identical quantities of water in identical containers under identical conditions such that the hot water freezes before the cold water. Incredibly, he was sometimes even able to observe this when starting with 100C water vs 0C water!
As you'd guess, there is a little bit of a trick to it, but it's one that not nearly as obnoxious as some of the earlier explanations: no evaporation resulting in a smaller volume or remaining water, no spontaneous ice spikes with greater surface area, and no differential melting of the thick layer of frost on the freezer shelf required.
Rather than giving a spoiler, I'll let the paper describe the exact technique he used. OK, a hint from the paper to encourage you to actually read it: cold water will indeed always reach 0C before identically handled hot water, but contrary to popular belief reaching 0C is merely a requirement for freezing rather than a guarantee.
Impressively, he describes a controlled duplicable setup in which he's able to reliably freeze (using an exact definition) identical quantities of water in identical containers under identical conditions such that the hot water freezes before the cold water. Incredibly, he was sometimes even able to observe this when starting with 100C water vs 0C water!
As you'd guess, there is a little bit of a trick to it, but it's one that not nearly as obnoxious as some of the earlier explanations: no evaporation resulting in a smaller volume or remaining water, no spontaneous ice spikes with greater surface area, and no differential melting of the thick layer of frost on the freezer shelf required.
Rather than giving a spoiler, I'll let the paper describe the exact technique he used. OK, a hint from the paper to encourage you to actually read it: cold water will indeed always reach 0C before identically handled hot water, but contrary to popular belief reaching 0C is merely a requirement for freezing rather than a guarantee.
I think it's because there is more gas in cold water. This results in ice that has more bubbles in it and conducts heat more poorly, and prevents the latent heat from being removed from the yet unfrozen parts of the water.
I googled around and found this paper to be far more compelling than any of Wikipedia's vague explanations:
http://arxiv.org/abs/1310.6514
Yeah, this paper seems to explain it reasonably well, although I don't fully understand it...maybe I'll re-read it sometime this week.
Bond relaxation was my first thought too.
Driving home once again, what an interesting and unusual molecule our ubiquitous friend 'water' really is. Polar, bent, and funky; expanding when frozen, incompressible as a liquid.
Is it truly incompressible, or just enough for practical uses?
It's not incompressible it's just that when you compress it, it will stay liquid and it's volume doesn't really decrease that much as the chart below shows.
http://engineering-references.sbainvent.com/thermodynamics/p...
http://engineering-references.sbainvent.com/thermodynamics/p...
It's only like ten times more compressible than diamond, if I remember my schooling correctly.
In liquid water, mechanical engineers are usually free to assume incompressability. This makes solving the math a lot easier, though absolutely cannot be done for gases.
In liquid water, mechanical engineers are usually free to assume incompressability. This makes solving the math a lot easier, though absolutely cannot be done for gases.
Well, even for gasses, your results are accurate enough as long as the Mach number is below 0.3: http://encyclopedia2.thefreedictionary.com/incompressible+fl...
This is not done in practice. Be careful getting engineering advice from the Free Dictionary.
It reflected what I was taught in fluid/gas dynamics courses for my degree, and you'll see the same point made in various other places.
"The compressibility of water reduces the sea level by about 40 m giving us 5% more land."
http://www.starfish.ch/reef/ocean.html
http://www.starfish.ch/reef/ocean.html
Nothing is truly incompressible.
Right, if something were truly incompressible, the speed of sound through it would be infinite and you could propagate signals through it faster than allowed by relativity.
I'm putting hot and room temperature water in my freezer...no way this will work.
The Royal Society for Chemistry ran a competition to come up with an explanation: http://www.rsc.org/learn-chemistry/resource/res00001018/the-...
Seriously you should use warm water to fill your if cube trays. Even if it doesn't freeze faster you get better ice cubes from having less dissolved gas.
As long as it's not hot/warm water from the faucet. Many water heaters can leach metals into the water and while safe for showering you shouldn't drink it. http://mobile.nytimes.com/2008/01/29/health/29real.html?refe...
More importantly they taste like crap.
They mention the difficulty of determining when the water is frozen, since water at zero degrees C can be either liquid or solid. It seems easy to solve by checking for an increase in volume or pressure, since we know that ice expands into more volume than liquid water.
If you track temperature over time you can tell when freezing starts and ends: when freezing starts, the temperature stops dropping, and it starts dropping again when freezing is complete.
nothing misterious really.. it only works where hot water turns more or less to steam ie very high surface area and thus can cool faster thus overtake cooler water droplets that have significantly less surface area.
After reading this article, I did some research on this topic and compiled some of the best resources I found here - http://knowledgemaps.org/learning-journey/1118/understanding...
Reminds me of an argument my brother and I used to have.
You pour two cups of tea. You add an exact amount of cold milk to one but not the other then wait five minutes. Then you pour the same amount of milk in the second cup. You stir both equally.
Which is colder?
You pour two cups of tea. You add an exact amount of cold milk to one but not the other then wait five minutes. Then you pour the same amount of milk in the second cup. You stir both equally.
Which is colder?
This one is simple. The more difference in temperature you have, the faster the liquid is cooled down. This means that you should first let the tea cool by itself for 5 minutes, then to cool it with milk to get the colder version.
This was presented as problem #15 (Cooling water) at IYPT 2000
As far as I remember, nobody confirmed effect experimentally at that time.
As far as I remember, nobody confirmed effect experimentally at that time.
I think I know why.
Good temperatures for showing the effect are 5 and 35 C.
5 C is near 4 C, the point at which water has maximum density.
Good temperatures for showing the effect are 5 and 35 C.
5 C is near 4 C, the point at which water has maximum density.
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Best explanation I saw was from Beakman's World, a 90's Tv show.
Sorry can't find a YouTube video.
Sorry can't find a YouTube video.
https://www.youtube.com/watch?v=pvgefs7J1rY
https://www.youtube.com/watch?v=ZGjwe-BCfms
To get the water to freeze into snow mid-air, you have to start with boiling water. Cold water won't freeze in time. I've even heard of research involving using boiling water in snow-making machines.