Why warm water freezing faster than cold water?

[positrones]

Why warm water freezing faster than cold water? Can somebody explain this?

[insane_alien]

http://en.wikipedia.org/wiki/Mpemba_effect this will start you off and give a basic overview of it.

 

the references go further indepth than the wiki article so you can try them if you want something more technical.

[Daecon]

Something to do with greater acceleration to freezing point, and so building up more "freezing" inertia, thus getting to 0 faster...?

 

Or is that just pseudoscience?

[insane_alien]

trans, where the hell did you come up with that? i don't know of anything like 'freezing inertia' certainly didn't cover it in thermodynamics lectures.

[Daecon]

Because the temperature drops faster, it ends up getting to freezing point slightly quicker than colder water, where the temperature doesn't drop as fast.

[swansont]

No, nothing like "freezing inertia." Read the entry. The effect depends on essentially having dissimilar conditions for the two samples.

[Norman Albers]

There will be more convection with the warm sample so conditions at the wall will be different. With a more calm, cold sample you can have delayed onset of the whole mass freezing if there was no spot favoring ice formation. Heat of fusion must be taken out once water is at freezing temperature. Usually freezing starts at the colder wall, or at the top where there is evaporation.

[gcol]

interesting and curious.

 

[

[ultma]

no one really knows it could be due to many factors

 

like dissolved oxygen for example

 

Hotter water having less dissolved Oxygen than cooler

 

Because the temperature drops faster, it ends up getting to freezing point slightly quicker than colder water, where the temperature doesn't drop as fast.

 

 

Thats rubbish:

The hotter water drops faster intialy due to the temperature difference beteween the water and the surroundings so eventualy it would reach the same point the coolder water was at and then drop at the same speed the cooler water did

[gcol]

It is called the Mbemba effect and is well documented, but the exact cause is the subject of controversy.

 

Plenty of google hits, including wiki.

[Daecon]

Yes, I'm guessing the "Or is that just pseudoscience?" comment was accurate then.

[Norman Albers]

I will not put warm water into my ice-cream maker with the salt!

[Externet]

Being a science mistery and also fact, I can only guess that has to do with the speed of heat transfer, by temperature gradient dt/ds.

 

The greater the temperature differential per unit of distance from the core of the heated water to the heat absorbing cold surfaces, the greater the 'motion' velocity of heat. But unable to elaborate on this.

 

Pouring the same amount of same water samples

-in deformable identical closed containers,

-then warming one up;

-and then suspending them both in a freezing chamber

-with no internal humidity

 

should get rid of the uncertainty about dissolved gases, evaporation, influence of intimacy of contact with freezer walls, and damp air affinity to

one of the containers.

 

Hope it has been tried that way...

 

Nope, cannot do it at home to try.

 

----Also read somewhere that to melt ice from a windshield, cold water works faster than hot. Is that related to the same effect

 

Miguel

[Daecon]

Being a science mistery and also fact, I can only guess that has to do with the speed of heat transfer, by temperature gradient dt/ds.

 

The greater the temperature differential per unit of distance from the core of the heated water to the heat absorbing cold surfaces, the greater the 'motion' velocity of heat. But unable to elaborate on this.

 

*cough*copycat*cough*

[Norman Albers]

Externet, Hot water will crack your windshield!!! So if cold water gets you there and hot water gets you ruined, we may say cold is faster.