Talk:Mpemba effect

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Diagram

I've added a relevant diagram (already available on Wikimedia Commons), and also expanded the Historical section a little, discussing the work of James Black. I know that this has been a contentious topic in the past, but I thought that it was worth gently revisiting; I've tried to be cautious, but might reasonably be accused of over-interpreting Farenheit's contributions in the light of subsequent knowledge; I'm also rather relying on Black's description of Farenheit's work, as my Latin isn't up to scratch. Cluebot archiving removed so that we can have a chat! Klbrain (talk) 12:04, 17 August 2015 (UTC)[reply]

No one seems to mention this as a possible cause

If you put something hot into a freezer it will switch the thermostat to turn the freezer on. This will cause the temperature inside the freezer to drop and so cause the water to turn to ice more quickly. There is hysteresis on these thermostats so they will reduce the temperature in the freezer to a lower temperature than the set temperature. To do a controlled test you would need to put the hot water ice cube trays cold ones in the same freezer at the same time. Why hasn't someone done this with a camera lens inside the freezer to monitor exactly when each one turns to ice? — Preceding unsigned comment added by Caparn (talk • contribs) 16:49, 9 May 2016 (UTC)[reply]

I would be WP:BOLD and do it myself but I'm not certain I could avoid doing so in a manner that would amount to original research. But if a youtube video from someone whose credentials consist of "some college" can be cited I'll go for it. Mattman00000 (talk) 13:01, 23 June 2016 (UTC)[reply]

interesting temperature

"containers at 35 and 5 °C (95 and 41 °F) to maximize the effect"

This 5 °C is roughly (as if rounded) where liquid water is at maximum density. Freezing from the higher temperature would require less expansion. The density change should also have an effect on entropy. — Preceding unsigned comment added by 97.104.88.146 (talk) 08:26, 22 May 2016 (UTC)[reply]

What is 'quantity'?

The article several times refers to the 'quantity' of water without specifying how this is defined. The Mpemba/Osborne experiments appear to have used volume as the measure of quantity. The other obvious measure would be mass (usually measured by weighing in standard conditions). Since the density (mass per unit volume) of water varies with temperature, the two measures are not equivalent, as a unit volume of water at a higher temperature will generally have less mass than the same volume at a lower temperature. Quantitatively the difference is probably too small to explain the alleged phenomena, but it seems desirable to avoid the ambiguity.86.132.140.164 (talk) 13:56, 7 December 2016 (UTC)[reply]

Name

Batholomeo or Bartholomeo ? — Preceding unsigned comment added by 188.238.242.155 (talk) 16:49, 18 December 2016 (UTC)[reply]

Probably with an r. For more information and external sources such as pp 7 and 11 of an FAO report see an old Wikipedia biography of Mpemba--Rumping (talk) 13:29, 16 February 2017 (UTC)[reply]

Talk archives

There are achieves of previous talk at Talk:Mpemba effect/Archives/ 1 and Talk:Mpemba effect/Archives/ 2 but I cannot see a link on these pages --Rumping (talk) 13:29, 16 February 2017 (UTC)[reply]

Added this in manually at the top of the talk page, as the usual template wasn't working with the non-standard archive naming (in the past)

Resolved

Klbrain (talk) 16:39, 2 April 2018 (UTC)[reply]

History

How mpemba effect operates

Nkungwej (talk) 14:52, 24 August 2017 (UTC)[reply]

A personal observation.

When I was a schoolteacher, one of the experiments we did with "special needs" children was to freeze water in a watch glass to make a lens. Demonstrating that it doesn't have to be glass - even ice can make a lens. The teachers'guide suggested that we teachers use near-boiling water for this, because such water contains very few dissolved gases and results in a much "clearer" lens, because in a good quality freezer the water would freeze too quickly for air to dissolve in it.

We were surprised to discover that near-boiling water froze about as quickly as room temperature water. I have no idea whether this is related.

Graph in Article

Isn't there a mistake in the graph? When a substance is changing phase, the temperature of the substances remains constant. In the graph, both the initially hot and initially cold water both show a constant temp, but it's not 0 C!!! Shouldn't that graph be removed? — Preceding unsigned comment added by 207.255.29.67 (talk) 03:36, 27 December 2017 (UTC)[reply]

It doesn't rather suggest that their temperature probe hadn't been properly zero'ed, but I think that the graph is still useful because it shows a plateau close to zero. I'd leave it in place until someone can find a better figure. Klbrain (talk) 16:42, 2 April 2018 (UTC)[reply]

Thermal eddy momentum and diffusivity via Turbulent Prandtl number?

This is just an armchair observation, but wouldn't greater temperature differential and thermal gradients that are further from equilibrium be responsible for creating thermal eddies, flows and momentum in either or both fluid turbulence and thermic turbulence? With a greater momentum, we see a flywheel effect of thermal distribution even as temperatures nearer equilibrium. See Turbulent Prandtl number. - 75.173.66.142 (talk) 20:27, 1 January 2018 (UTC)[reply]

External links modified (February 2018)

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Photos

There are two photos, purporting to lend evidence to this effect. The caption on one states "Mpemba effect experiment: the hot water contained in a thermos, if thrown into the air in a very cold environment, freezes instantly before touching the ground."

This is not a very helpful caption for two reasons: 1) water cannot freeze "instantly," and 2) where's the evidence that it freezes before it hits the ground? Photos or videos of throwing hot water into very cold air show a lot of condensation, and a lot of droplets so it can look very spectacular, especially when backlit. But they never show that the droplets are frozen.

Is there evidence that the water freezes before it hits the ground?

Hermanoere (talk) 18:43, 24 October 2018 (UTC)[reply]