positrones Posted July 17, 2007 Share Posted July 17, 2007 Why warm water freezing faster than cold water? Can somebody explain this? Link to comment Share on other sites More sharing options...
insane_alien Posted July 17, 2007 Share Posted July 17, 2007 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. Link to comment Share on other sites More sharing options...
Daecon Posted July 17, 2007 Share Posted July 17, 2007 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? Link to comment Share on other sites More sharing options...
insane_alien Posted July 17, 2007 Share Posted July 17, 2007 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. Link to comment Share on other sites More sharing options...
Daecon Posted July 17, 2007 Share Posted July 17, 2007 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. Link to comment Share on other sites More sharing options...
swansont Posted July 17, 2007 Share Posted July 17, 2007 No, nothing like "freezing inertia." Read the entry. The effect depends on essentially having dissimilar conditions for the two samples. Link to comment Share on other sites More sharing options...
Norman Albers Posted July 17, 2007 Share Posted July 17, 2007 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. Link to comment Share on other sites More sharing options...
gcol Posted July 17, 2007 Share Posted July 17, 2007 interesting and curious. [ Link to comment Share on other sites More sharing options...
ultma Posted July 17, 2007 Share Posted July 17, 2007 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 Link to comment Share on other sites More sharing options...
gcol Posted July 17, 2007 Share Posted July 17, 2007 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. Link to comment Share on other sites More sharing options...
Daecon Posted July 18, 2007 Share Posted July 18, 2007 Yes, I'm guessing the "Or is that just pseudoscience?" comment was accurate then. Link to comment Share on other sites More sharing options...
Norman Albers Posted July 18, 2007 Share Posted July 18, 2007 I will not put warm water into my ice-cream maker with the salt! Link to comment Share on other sites More sharing options...
Externet Posted July 19, 2007 Share Posted July 19, 2007 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 Link to comment Share on other sites More sharing options...
Daecon Posted July 19, 2007 Share Posted July 19, 2007 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* Link to comment Share on other sites More sharing options...
Norman Albers Posted July 19, 2007 Share Posted July 19, 2007 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. Link to comment Share on other sites More sharing options...
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