How can boiling water freeze faster than water at room temp?

[sophiecentaur]

(where did they put it to freeze it?

I believe they used shallow ponds which freeze over during cold desert nights. The ice was skimmed off and taken to cold caves with straw insulation. That way, wealthy Arabs could have iced drinks at noon in the desert. What a status symbol! Added salt could give them a freezing mixture.

 

[Buckleymanor]

I believe they used shallow ponds which freeze over during cold desert nights. The ice was skimmed off and taken to cold caves with straw insulation. That way, wealthy Arabs could have iced drinks at noon in the desert. What a status symbol! Added salt could give them a freezing mixture.

https://en.wikipedia.org/wiki/Ice_house_(building)https://en.wikipedia.org/wiki/Ice_house_(building)

 

[nasu]

I believe they used shallow ponds which freeze over during cold desert nights. The ice was skimmed off and taken to cold caves with straw insulation. That way, wealthy Arabs could have iced drinks at noon in the desert. What a status symbol! Added salt could give them a freezing mixture.

Where did the Arabs come from? In Aristotle?
I tried to see what he did actually said. It's not easy because the references indicate just the book not any section or page (they did not have pages in their scrolls, I suppose),]
In his book "Meteorology" I found (Book 1, part 12) the claims that people heat water in the sun so it cools down faster. He does not explain who does it and where the idea comes from.
And also mentions the practice of the inhabitants of the Pontus to pour hot water on their reeds when they go ice fishing. The claim is that it will freeze faster.
Does not say if he really went there or just heard it from storytellers.
Pontus is somewhere is today Turkey but at that time there were no Arabs (and no dessert) over there.
Maybe he mention Arabs somewhere else.

 

[A.T.]

I don't know - it wasn't demonstrated. But while it may be similar if you are correct in your prediction, it strains the description of the effect and doesn't lend itself well to quantitative measurement of what is happening.

Yes, it probably doesn't even fit direct freezing:
https://www.metabunk.org/debunked-b...-you-throw-it-in-the-air-at-40-degrees.t2902/

 

[mohamed el teir]

" The behaviour seems contrary to natural expectation but many explanations have been proposed.

• Evaporation: The evaporation of the warmer water reduces the mass of the water to be frozen. Evaporation is endothermic, meaning that the water mass is cooled by vapor carrying away the heat, but this alone probably does not account for the entirety of the effect.
• Convection: Accelerating heat transfers. Reduction of water density below 4 °C (39 °F) tends to suppress the convection currents that cool the lower part of the liquid mass; the lower density of hot water would reduce this effect, perhaps sustaining the more rapid initial cooling. Higher convection in the warmer water may also spread ice crystals around faster.
• Frost: Has insulating effects. The lower temperature water will tend to freeze from the top, reducing further heat loss by radiation and air convection, while the warmer water will tend to freeze from the bottom and sides because of water convection. This is disputed as there are experiments that account for this factor.
• Supercooling: It is hypothesised that cold water, when placed in a freezing environment, supercools more than hot water in the same environment, thus solidifying slower than hot water. However, super-cooling tends to be less significant where there are particles that act as nuclei for ice crystals, thus precipitating rapid freezing.
• Solutes: The effects of calcium carbonate, magnesium carbonate among others.
• Thermal conductivity: The container of hotter liquid may melt through a layer of frost that is acting as an insulator under the container (frost is an insulator, as mentioned above), allowing the container to come into direct contact with a much colder lower layer that the frost formed on (ice, refrigeration coils, etc.) The container now rests on a much colder surface (or one better at removing heat, such as refrigeration coils) than the originally colder water, and so cools far faster from this point on.
• Dissolved Gases: Cold water can contain more dissolved gases than hot water, which may somehow change the properties of the water with respect to convection currents, a proposition that has some experimental support but no theoretical explanation. "

source: https://en.wikipedia.org/wiki/Mpemba_effect#Suggested_explanations

 

[sophiecentaur]

Where did the Arabs come from? In Aristotle?

I was making a point that the technology was there, long before Electrolux.
But your doubt about the experimental evidence is probably well founded. I understand that a lot of Greek Science was based on simple observation without actually setting up experiments. I believe that it was not until the middle ages that the Scientific method actually required exhaustive experimentation so Aristotle may well have relied on hearsay.
That binghampton paper seems to be a pretty competent bit of work and a lot more believable than statements from the ancient past.

 

[Neon]

Think about it. Boiling water evaporates very fast.It could have evaporated more than the room temperature one and have to absorb less heat.Some may argue that the difference would not have affected that much but remember, the water in two containers AREN'T the EXCAT same. The ions? The volume? If a more controlled experiment is done,I'm sure a different result will be achieve.

 

[Neon]

And also evaporation takes heat away and there is no way to stop that so we can say hot water 'cheated'

 

[Nemika]

I haven't read all the posts nor I am an expert but if we think in this way that water is a strange liquid.
1. It expands anomalously and therefore the Mpemba effect might be correct.
2. On freezing, water molecules arrange themselves in hexagonal structures with hollow space in between them. I think that on heating the water molecules move more freely and so they are easily able to arrange themselves in this structure form.
3. And yes I do believe that larger surface area/volume ratio of hot water also contributes in rapid heat loss from it.

 

[rootone]

And also evaporation takes heat away and there is no way to stop that so we can say hot water 'cheated'

Put the two samples into sealed containers instead of open ones?
(Best would something like clear plastic so that fracturing can't happen due to pressure or ice, but you can still see what is happening.)

 

[sophiecentaur]

If a more controlled experiment is done,I'm sure a different result will be achieve.

Did you read all the links in this thread? There have already been many investigations and the results have been very dependent on the conditions and it depends on how you determine the 'freezing' has taken place.

 

[DrClaude]

I think this thread has run its course. I encourage everyone interested in the subject to read the Brownridge paper cited in post 24.https://www.physicsforums.com/threa...-then-water-at-room-temp.839800/#post-5270349

Thread locked.