Build an ice tray of a material that has a large heat capacity but can quickly transfer heat away from the water. Make the shape to maximize surface area as much as still allows the ice to slide out easily. Keep the ice tray frozen when not in use. This will permit rapid freezing. of water.
-- Voice, Sep 13 2006

Mpemba effect explained http://www.math.ucr...eral/hot_water.html
[xandram, Sep 13 2006]

Pixie dust http://www.weeklywo...ures/politics/61725
[fridge duck, Sep 13 2006]

A more recent publication http://lanl.arxiv.o...df/0512/0512262.pdf
Also from Monwhea Jeng [jmvw, Sep 16 2006]

Mpemba is a punk! http://www.loraxhav...ceCube/IceTest.html
I tested it. Just today. Hah! [Galbinus_Caeli, Sep 20 2006]

Want to suggest what that material might be?

I think you'll find it will make the ice tray too bulky for practical use, and offer no improvements over current ice makers.
-- DrCurry, Sep 13 2006


tsk, tsk. Hot water freezes faster than cold, known as the Mpemba effect. [see link]
-- xandram, Sep 13 2006


> Hot water freezes faster than cold
... sometimes, under certain specific circumstances.
What an interesting link - thanks!

Hm, I really want this to be a mythbusters episode with a heat camera in a refrigerator.
-- jutta, Sep 13 2006


Fascinating link [xandram]. I had heard about that and had always assumed it to be bollocks.

Now that I've read it on the internet, I acknowledge that it must be true.
-- Texticle, Sep 13 2006


On that note, [Texticle], have you heard about the recent military use of pixie dust?
-- fridge duck, Sep 13 2006


umm, (lots of coughing) I had only vaguely remembered it from high school, I'm glad others enjoyed it...esp. [jutta] btw cool idea about the fridge.
-- xandram, Sep 13 2006


Make the ice tray in two layers, and circulate salt water inside it - might work.
-- neelandan, Sep 16 2006


Mpemba effect is cool! Perhaps this has to do with autoionization. Hot water contains more H3O+ and OH- ions. Perhaps, when the water is rapidly cooled, these ions will stay around a little while and lower the freezing point the same way salt does. Perhaps this affects the freezing process.
-- jmvw, Sep 16 2006


//Make the shape to maximize surface area as much as still allows the ice to slide out easily.// Spherical?

[xandram]I like the link too...presumably... it must contract/expand in a stangewa, too. I wonder if that's got clever uses
-- Dub, Sep 16 2006


Hot water does not freeze faster than cold, it merely begins to cool faster while its still warm. And a sphere minimizes surface area.
-- Voice, Sep 19 2006


If your ice tray was cold enough, you wouldn't even need to put it in the freezer. I think that the Mpemba effect can cause you no harm in this case.
-- GutPunchLullabies, Sep 19 2006


[Voice] did you actually read the link?

Not really sure of it myself, it's counterintuitive from both logical and thermodynamic standpoints, but hey so are a lot of things.

I think you'll find it easier to make your freezer colder/introuduce some convective cooling in the same way that a convection oven increases heat transfer for a given temperature difference.

Otherwise, I'd have a void in the ice tray with something like antifreeze in it. Have the freezer temperature such that the antifreeze (or whatever) is frozen (just) when it's ready for use. Then the phase change of the antifreeze is your heat well. Ie you have large effective heat capacity. This is the most mass efficient way I can think of. Other than using heat of vapourisation, such as having a gas that liquefies/boils at say -10 degrees as your heat well. pre-charge the ice tray with the gas, then pour in the water. the heat of vapourisation is generally huge, and a small ammount of vapourising gas should freeze a proportionately large ammount of water. the problem is scavenging your coolant and reusing it, in a remotely energy/mass efficient way. A short chain hydrocarbon of some sort might fit the bill.

Or just have a tank of liquid CO2 on hand for those emergency "I need ice NOW" situations. using controlled boiling and expansion of the CO2 through a coupled nozzle/evaporator of some sort should allow you to snap freeze water very quickly. And expensively.

good luck, I like this idea.
-- Custardguts, Sep 20 2006


All right, I had to test the Mpemba effect and see what happened. See link for my results.
-- Galbinus_Caeli, Sep 20 2006


Let's recap on the original idea. You need a tray with large thermal mass and high conductivity. This pretty much leads us directly to a metal tray. Which have existed about as long as mechanical refrigeration.

You can make one a bit more thick for even faster freezing, but at some point it will be too heavy. There is an issue with ice that tastes like metal, but a thin coating of, say, teflon would fix that - perhaps without killing the conductivity.
-- Worldgineer, Sep 20 2006


Stainless steel.
-- Texticle, Sep 20 2006


White gold.
-- GutPunchLullabies, Sep 21 2006


Go for serious density. Depleted uranium.
-- Galbinus_Caeli, Sep 21 2006



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