Making ice cubes

Why does it take warm water less time to turn into ice cubes than cold water?

http://en.wikipedia.org/wiki/Mpemba_effect

Originally posted by FMF
Why does it take warm water less time to turn into ice cubes than cold water?

The only effect that will do that is if the ice cube tray full of warm water is put on an icy floor of the freezer shelf. The warm water causes the tray to sink through the ice layer which is a fair heat insulator and get the tray closer to the cooling coils where the temperature is much colder. Thermodynamics forces water to delay the transition from liquid to solid (the energy of fusion) until the temperature of the water gets to zero degrees C, assuming two ice cube trays are put in the same freezer, but one at 100 degrees C and one already at 0 degrees C, and put directly on the cooling coils, the heated water will ALWAYS take longer to get to 0 degrees C than the tray already at 0 C.

I don't make ice-cubes, my walk in fridge/freeer does it automatically.

http://home.howstuffworks.com/icemaker1.htm

-m.

Originally posted by Metal Brain
http://en.wikipedia.org/wiki/Mpemba_effect

http://www.redhotpawn.com/board/showthread.php?threadid=141247

Originally posted by sonhouse
assuming two ice cube trays are put in the same freezer, but one at 100 degrees C and one already at 0 degrees C, and put directly on the cooling coils, the heated water will ALWAYS take longer to get to 0 degrees C than the tray already at 0 C.

Rather obviously; even the fastest time is slower than "already there".

But now try the experiment at 20 °C and 40°C, and use "frozen solid" instead of "reached 0 °C in some part of the container" as the criterion. Repeat for a variety of liquids and suspensions (such as ice cream... always a good excuse for a scientific experiment 😉). You may be surprised - many people have been.

Richard

Originally posted by Shallow Blue
Rather obviously; even the fastest time is slower than "already there".

But now try the experiment at 20 °C and 40°C, and use "frozen solid" instead of "reached 0 °C in some part of the container" as the criterion. Repeat for a variety of liquids and suspensions (such as ice cream... always a good excuse for a scientific experiment 😉). You may be surprised - many people have been.

Richard

Good luck with that. Removing heat is a simple exercise in thermodynamics. You think you are going to get something for nothing? Not sure why you even push this stuff.

I never said 'reaching 0 C in some part of the container'. I said ice. surely you heard of the energy of fusion concept, eh. You know full well you have to remove more heat from water after it is already at 0 C to get that water to convert to ice even though the temperature stays right at 0 C.

Originally posted by FMF
Why does it take warm water less time to turn into ice cubes than cold water?

Related question: I fill four plastic ice cube trays with water, stack them in the freezer in no particular order, and the next day pop them out into a bin. They easily pop out as nice whole cubes from the tray on top, but not quite so easily, and with some breakage, from the next tray down, etc. until the bottom tray, which yields broken cubes and partial cubes staying stuck in the tray and a whole lot of twisting needed even for that.

Why is this?

Originally posted by JS357
Related question: I fill four plastic ice cube trays with water, stack them in the freezer in no particular order, and the next day pop them out into a bin. They easily pop out as nice whole cubes from the tray on top, but not quite so easily, and with some breakage, from the next tray down, etc. until the bottom tray, which yields broken cubes and partial cubes staying stuck in the tray and a whole lot of twisting needed even for that.

Why is this?

Sounds like you have a freezer with an air blower and the air gets to the top layer first, freezes them first and the ones below are partially insulated by the ones on top.

Originally posted by sonhouse
Sounds like you have a freezer with an air blower and the air gets to the top layer first, freezes them first and the ones below are partially insulated by the ones on top.

It does have a blower. Maybe faster freezing and "stickiness" of the cubes are related. Time to start experimenting. Of course the resulting cubes will be used in experiments on alcohol solutions. 🙂

Originally posted by JS357
....with some breakage, from the next tray down, etc. until the bottom tray, which yields broken cubes and partial cubes staying stuck in the tray and a whole lot of twisting needed even for that. Why is this?

Maybe you're just in too much of a hurry to make yourself that G & T?

Originally posted by FMF
Maybe you're just in too much of a hurry to make yourself that G & T?

LOL !! 😀

Originally posted by JS357
Related question: I fill four plastic ice cube trays with water, stack them in the freezer in no particular order, and the next day pop them out into a bin. They easily pop out as nice whole cubes from the tray on top, but not quite so easily, and with some breakage, from the next tray down, etc. until the bottom tray, which yields broken cubes and partial cubes staying stuck in the tray and a whole lot of twisting needed even for that.

Why is this?

Perhaps it's to do with the rate at which the water freezes in the different trays. Maybe ice is subject to the same stress issues that metal has when it solidifies?

Originally posted by sonhouse
Good luck with that. Removing heat is a simple exercise in thermodynamics. You think you are going to get something for nothing? Not sure why you even push this stuff.

I am "pushing" nothing. I merely note that many people, quite a lot of them more intelligent than you and I, have tried the experiment and got surprising results. I repeat: try the experiment. You can theorise about how the universe ought to work according to your perfect and finished theory of thermodynamics. The ancient Greek natural philosophists were great lovers of this method - that's why they never did agree on whether there were four, five, two, or only one element. Modern science prefers to do the experiment, because it is more interested in how the world does work, and then find a theory which explains the observed phenomena.

I never said 'reaching 0 C in some part of the container'. I said ice.

And I quote, literally, from your previous post:

the heated water will ALWAYS take longer to get to 0 degrees C

Note: "get to 0 degrees C", not "ice". Literal quote. Make your mind up. As you explained quite lucidly just now, there is a difference between just reaching zero C, and freezing through - and this difference could easily make a difference to the result of the experiment.
The original observation, by the way, was about freezing solid, not about merely reaching freezing point, so I do believe that this should be our criterion as well.

Richard