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07-03-2012, 01:28 PM   #31
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
 Originally Posted by masque de Z i tried this evening to freeze faucet water and it took 160-164 min (obviously i couldnt be opening freezer all the time so i am guessing a bit earlier than i opened it last based on the time of the prior test and the condition of the ice that had started to form from the perimeter of the can first to full disk eventually to build 2 mm thick ice wall at the top (water below ) (so lets define this as the reference).
Check your freezer temperature. Taking almost 3 hours to get a 2mm thick layer of ice sounds like it's taking way too long. It would take forever to make a tray of ice at that rate. (Or maybe I'm just misreading your run-on sentence.)

I think household freezers should be running at close to 0 degrees F.

 07-03-2012, 02:25 PM #32 veteran     Join Date: Aug 2009 Location: Stanford, CA USA Posts: 3,319 Re: Can SMP Solve the Mpemba Effect mystery? No my freezer works ok although old. It is about -15c and it has a lot of meat and frozen vegetables ice cream etc in it so its not empty which should help i think. But when you place a can and its not in contact from all sides but only with the air of the container and the bottom part of its surface it takes a long time. Also a tray of ice probably happens faster because the contact area for the water you use is a lot bigger in relation to the volume. Its like 5a^2 vs a^3 and for the cylinder its 2*pi*R*H +pi*R^2 vs pI*R^2*H. So if a for the ice tray is 5-6 times smaller than the cylinder's R or H you get the picture. Also the air inside the freezer must quickly arrive at the overall temperature of the system when opened and closed due to small overall mass exchanged. So maybe one can use all surface (eg above equations) although i expect the metal contact to be doing much better job in cooling than the air molecules above. Last edited by masque de Z; 07-03-2012 at 02:31 PM.
07-03-2012, 02:41 PM   #33
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
 Originally Posted by masque de Z No my freezer works ok although old. It is about -15c and it has a lot of meat and frozen vegetables ice cream etc in it so its not empty which should help i think. But when you place a can and its not in contact from all sides but only with the air of the container and the bottom part of its surface it takes a long time.
Something just doesn't seem right to me... 3 hours to get 2mm of ice on top of a half liter of water just seems really slow, and this has nothing to do with the Mpemba question.

 07-03-2012, 03:01 PM #34 veteran     Join Date: Aug 2009 Location: Stanford, CA USA Posts: 3,319 Re: Can SMP Solve the Mpemba Effect mystery? Try it, put in your freezer similar volume in a container and let it rest and report how long it takes. I know my food is pretty cold because it takes forever to thaw when i take chicken or steaks out which wouldn't be the case if the temperature was very close to say -2 or -3. It it is indeed pretty low as i said around -15. But as i said when you put food or ice trays you let the mass rest having very small height (in packets) so it has much more available surface area for its mass than similar mass water in a cylinder. I mean if as i said i try to place a plastic storage bag filled with 100ml water resting flat on the surface of the freezer it will obviously take 1h or so maybe less. In fact i have frozen vinegar as part of another test within minutes in a small r=2cm disk cup-height 0.5cm (way much less volume) . Of course not having the exact same surface in both runs makes the freezer bag example a problem to test. In any case none of these bs in my opinion references in wikipedia describe what they did and what they got as results. So i call these references bs not because they are lies necessarily but because as presented they do nothing to illuminate the reader on what the hell they measured. Wouldnt you expect some numbers in an article like that? For a phenomenon like that in the media recently you would expect an article that has some exact data in it and yet where is it??? Give me some numbers minutes , hours, how it was done, what was defined as frozen to stop time etc.Where is all this in the wikipedia entry??? I will do a lot more tests now that i am curious but you also try your own and report so that we get a better picture. Maybe i must try a lot less water next in a much different shape container (eg a small disk plate like the vinegar thing above to see if then the fact it happens a lot faster defines the difference better. Still curious how on earth Aristotle would have known any of it using what cooling method? lakes? snow?
 07-03-2012, 03:25 PM #35 veteran     Join Date: Aug 2009 Location: Stanford, CA USA Posts: 3,319 Re: Can SMP Solve the Mpemba Effect mystery? Ok lets try to read this article to see if it has more illuminating details about what the experiments are like and some theory too. http://arxiv.org/pdf/0704.1381v1.pdf
07-03-2012, 03:32 PM   #36
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
 Still curious how on earth Aristotle would have known any of it using what cooling method? lakes? snow?
"Through the ages, the seasonal harvesting of snow and ice was a regular practice of most of the ancient cultures: Chinese, Greeks, Romans, Persians. Ice and snow were stored in caves or dugouts lined with straw or other insulating materials. "

-wiki

07-03-2012, 03:33 PM   #37
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
 Originally Posted by masque de Z Try it, put in your freezer similar volume in a container and let it rest and report how long it takes. I know my food is pretty cold because it takes forever to thaw when i take chicken or steaks out which wouldn't be the case if the temperature was very close to say -2 or -3. It it is indeed pretty low as i said around -15.
As I said earlier, household freezers should be running at about 0 F = -18C, so you're actually little warm. I don't think it's warm enough to make a huge difference in freezing times, but your freezer is not running "pretty low."

Also, meats freeze solid at temperatures lower than -2 or -3 C because there are lots of dissolved solids in the water of meat products. I think turkeys freeze solid at around 25 F = -4 C or so.

 07-03-2012, 04:25 PM #38 veteran     Join Date: Aug 2009 Location: Stanford, CA USA Posts: 3,319 Re: Can SMP Solve the Mpemba Effect mystery? So i guess ice harvesting even in Greece could work probably north in the real historical Macedonia that Aristotle spent some time of his life and where winters bring snow that lasts many months like it does in North America (but of course never in coastal/central California etc only in mountains). This looks impressive too for the old timers; http://en.wikipedia.org/wiki/Icehouse_%28building%29 Which of course makes it interesting now to ask; If i have a mountain north and can bring down to the valley snow and store say 90% of it before it melts in a properly insulated house how long will it last if the weather outside is typical 20c or 10C or even 5C if its say not summer. I mean i read the references but i still would like some real numbers of how it worked (since it was in use until modern times and they could therefore check it then) But my argument is that if Aristotle and others were able to use even without describing to you how they personally did it without modern refrigeration the best they could have is some snow house at -2-3C? If they still could experience the effect it must be pretty easy to reproduce in a freezer today! http://www.jphs.org/locales/2004/6/2...aica-pond.html I wonder what kind of low temperature they could have achieved with the ice houses anyway. Some of the insulation used was pretty thick.
07-03-2012, 05:09 PM   #39
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
 Originally Posted by masque de Z But my argument is that if Aristotle and others were able to use even without describing to you how they personally did it without modern refrigeration the best they could have is some snow house at -2-3C?
I think the first mistake is to think of the ice as being at close to 0C to begin with. It was probably much, much colder. This would make the ice house much colder than -3C. It's not that the ice was "maintained" at a constant temperature. It was very cold, and then over time it got less cold while still being colder than 0C.

Also, have you lived anywhere that it snows? Have you ever seen snow and ice sit in a shaded valley for a week without melting*, even though it's not that cold out?

* That is, without completely melting away.

07-03-2012, 05:24 PM   #40
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
 Originally Posted by masque de Z So i guess ice harvesting even in Greece could work probably north in the real historical Macedonia that Aristotle spent some time of his life and where winters bring snow that lasts many months like it does in North America (but of course never in coastal/central California etc only in mountains). This looks impressive too for the old timers; http://en.wikipedia.org/wiki/Icehouse_%28building%29
My grandfather used to work on an ice camp in northern Wisconsin driving teams of oxen. They would harvest ice from frozen lakes to sell in the cities to use for refrigeration. People would have "ice boxes" which in those days were literally insulated boxes that held ice, and the ice man would come and deliver the ice every day.

Last edited by BruceZ; 07-03-2012 at 05:51 PM.

07-03-2012, 06:53 PM   #41
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Re: Can SMP Solve the Mpemba Effect mystery?

Quote:
 Originally Posted by Aaron W. As I said earlier, household freezers should be running at about 0 F = -18C, so you're actually little warm. I don't think it's warm enough to make a huge difference in freezing times, but your freezer is not running "pretty low." Also, meats freeze solid at temperatures lower than -2 or -3 C because there are lots of dissolved solids in the water of meat products. I think turkeys freeze solid at around 25 F = -4 C or so.
Oh i am not disputing that meats freeze easy at -3-4 etc (most food is water anyway) , just that my meats take forever to thaw something that doesnt happen if they were just -3,-4,-5. So yes i am sure its <-15 or so and i will measure it next and find out for sure but -15, -18 or -24 that i have had before isnt the main issue, geometry and placement and size are!

Back from measuring mine where i did the freezing and came at -17 C or so, the -15 C was a guess. The point being that the equipment was capable for that low, its simply that in my first experiment the process was slow due to the size/geometry and neighboring material contact of the container that had the water. As i said a small plate or even a full spoon will freeze water much much faster than a bottle or can.

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