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I have balls made of ICE
Posted by: guitarist
Date: February 25, 2010 10:33AM
A cool accessory from The Museum of Modern Art online store. I orderd a couple, and have tried freezing some to see how they come out, it works pretty well! Takes a little trial and error to get perfect spheres. Some are imperfect, but with a little finesse, they get more consistent.

My wife said she first encountered these in a swank Bourbon Bar in Tokyo. As it turns out, this ice tray is a Japanese designed and manufactured. It's a good price for what is essentially a novelty item.

They probably are perfect for an iced cocktail, where you don't want the ice to melt too fast. These are said to last longer and shed less water into a drink. For the bourbon or scotch lovers, I recommend these. Great conversation item.


[www.momastore.org]


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Re: I have balls made of ICE
Posted by: H1N1
Date: February 25, 2010 10:52AM
Cheaper
[www.housewaresandbeyond.com]#

Cheap
[www.gourmac.com]

Not Cheap
[www.japantrends.com]
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Re: I have balls made of ICE
Posted by: kap
Date: February 25, 2010 10:59AM
Interesting.



SoCal for now.
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Re: I have balls made of ICE
Posted by: Filliam H. Muffman
Date: February 25, 2010 11:02AM
You can make nearly perfectly clear ice cubes if you fill the tray with distilled water.



In tha 360. MRF User Map
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Re: I have balls made of ICE
Posted by: iaJim
Date: February 25, 2010 11:02AM
I really like those! I can see them in my scotch glass.
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Re: I have balls made of ICE
Posted by: Z
Date: February 25, 2010 11:08AM
Or would you rather no dilute your scotch at all?
[www.thinkgeek.com]
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Re: I have balls made of ICE
Posted by: Rick-o
Date: February 25, 2010 11:40AM
Heh! I like those round "cubes" too!

The Whiskey Stones just seem wrong to me. Almost reminds me of bouillon cubes dissolving in that glass.



Mr. Lahey: A lot of people, don’t know how to drink. They drink against the grain of the liquor. And when you drink against the grain of the liquor? You lose.

Randy: What the @#$%& are you talking about?
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Re: I have balls made of ICE
Posted by: billb
Date: February 25, 2010 11:41AM
I guess that's one way to finally grow a pair.angel smiley

Does the mold come in a color besides pink sandalwood ?
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Re: I have balls made of ICE
Posted by: freeradical
Date: February 25, 2010 12:01PM
OK math geeks.

Two objects, a sphere and a rectangle have the same volume.

Which has the greatest surface area?

And is the difference big enough to make a difference in how fast something melts?



Edited 1 time(s). Last edit at 02/25/2010 12:01PM by freeradical.
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Re: I have balls made of ICE
Posted by: Z
Date: February 25, 2010 12:23PM
Yes, surface area makes a difference in how fast it melts.

Sphere volume: 4/3*pi*r^3
Sphere surface area: dr(volume) = 4*pi*r^2

Cube (e.g. a three dimensional 'rectangle') volume: L^3
Cube surface area: 6L^2

Assuming a cube volume of 1 cubic unit, e.g. a length of 1 unit, the cube surface area is 6 square units.

Sphere radius with a volume of 1 cubic unit is (3/4/pi)^(1/3) = 0.62 units.
Sphere surface area is: 4*pi*0.62^2 = 4.84 square units.

Thus a cube has 24% greater surface are per unit volume than a sphere does. Is this enough to make a difference? Yes.

Greater surface area will allow for greater heat flux, which will result in faster melting. Just like why you cut up vegetables into smaller pieces so that they cook evenly, rather than just tossing them in whole.

... but you were just funning. grinning smiley



Edited 1 time(s). Last edit at 02/25/2010 12:30PM by Z.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 01:31PM
Yes, but the melting is primarily determined by heat gain from/around the glass, not the shape of the ice. If spherical ice melts more slowly the drink isn't being kept as cold.

Once the liquid is at 32 degrees it doesn't matter what shape the ice is if the drink is kept stirred so that the liquid stays at a uniform temperature, assuming there is enough surface area to absorb heat at the same rate as the liquid absorbs it from the glass and the air.

Or, it takes longer for the ice to cool the drink if the melting rate is lower because of the shape of the ice.

Nice novelty though.



- Winston



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: Mike V
Date: February 25, 2010 02:41PM
I don't get it?

If the ice has less surface area and doesn't melt as fast, then the drink isn't being cooled as well.

You could just use less ice cubes.

I appreciate that it looks different though.



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Re: I have balls made of ICE
Posted by: Z
Date: February 25, 2010 04:43PM
The liquid will get to temperature pretty quickly, then you want them to melt slowly (typically) so that you can enjoy your drink.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 05:12PM
Quote
Z
The liquid will get to temperature pretty quickly, then you want them to melt slowly (typically) so that you can enjoy your drink.

But how fast the ice melts doesn't depend on the shape of the ice. It does depend on things like whether you put a napkin around the glass, thickness of the glass, air temperature, etc. Perhaps at the margin there is some tiny difference with the part of the ice which is floating clear of the liquid. Spherical ice might help there, but I'd guess the difference would be hard to measure.

Now, if you don't stir or swirl the drink, and don't mind that it's warmer around the edges, spherical ice might melt a bit more slowly. But it won't be keeping the drink as cold.


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: MikeF
Date: February 25, 2010 05:29PM
The original link has big balls. The cheap/cheaper alternatives are small balls. Some people prefer bigger balls.
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 06:22PM
Quote
Z
Yes, surface area makes a difference in how fast it melts.

Sphere volume: 4/3*pi*r^3
Sphere surface area: dr(volume) = 4*pi*r^2

Cube (e.g. a three dimensional 'rectangle') volume: L^3
Cube surface area: 6L^2

Assuming a cube volume of 1 cubic unit, e.g. a length of 1 unit, the cube surface area is 6 square units.

Sphere radius with a volume of 1 cubic unit is (3/4/pi)^(1/3) = 0.62 units.
Sphere surface area is: 4*pi*0.62^2 = 4.84 square units.

Thus a cube has 24% greater surface are per unit volume than a sphere does. Is this enough to make a difference? Yes.

Greater surface area will allow for greater heat flux, which will result in faster melting. Just like why you cut up vegetables into smaller pieces so that they cook evenly, rather than just tossing them in whole.

... but you were just funning. grinning smiley

I knew the answer without doing the math (not that I couldn't do it if I had to): A sphere presents the smallest possible surface area for a given volume.



It is what it is.
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 06:33PM
Quote
Winston
But how fast the ice melts doesn't depend on the shape of the ice. It does depend on things like whether you put a napkin around the glass, thickness of the glass, air temperature, etc. Perhaps at the margin there is some tiny difference with the part of the ice which is floating clear of the liquid. Spherical ice might help there, but I'd guess the difference would be hard to measure.

Now, if you don't stir or swirl the drink, and don't mind that it's warmer around the edges, spherical ice might melt a bit more slowly. But it won't be keeping the drink as cold.

How fast the ice melts depends on a number of factors, including the surface area of the ice. The factors you list (air temperature, glass thickness, insulation i.e. napkin around the glass) determine the rate at which heat enters the liquid; the surface area of the ice cube and the temperature delta between the ice and the liquid determine the rate at which the ice absorbs heat from the liquid. For pieces of ice with a given volume, all other factors being equal the piece of ice with the greatest surface area will melt fastest.



It is what it is.
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Re: I have balls made of ICE
Posted by: H1N1
Date: February 25, 2010 07:48PM
Quote
MikeF
The original link has big balls. The cheap/cheaper alternatives are small balls. Some people prefer bigger balls.
hitting you in the face?
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 08:07PM
Quote
N-OS X-tasy!
How fast the ice melts depends on a number of factors, including the surface area of the ice. The factors you list (air temperature, glass thickness, insulation i.e. napkin around the glass) determine the rate at which heat enters the liquid; the surface area of the ice cube and the temperature delta between the ice and the liquid determine the rate at which the ice absorbs heat from the liquid. For pieces of ice with a given volume, all other factors being equal the piece of ice with the greatest surface area will melt fastest.

That doesn't sound right to me. If all other factors are equal, there will be a fixed rate of transfer of heat from the surroundings into the liquid, hence a fixed rate of melting of the ice. The only exception would be if there is not enough surface area of ice to keep the liquid at 32 degrees. But if there is enough ice to keep the liquid at 32 degrees, only enough ice will melt in a given time to maintain that equilibrium. It won't matter how the ice is shaped, as long as enough of it can melt to keep the 32 degrees.

If ice didn't cool by conversion of solid to liquid you'd be right. But ice doesn't primarily cool because it's cold, it cools from the phase change from solid to liquid. So the amount of melting is directly related to the heat transfer into the drink from outside.

Edit: To clarify, if there is not enough ice to keep the drink at 32 degrees, then a chunk of ice with a larger surface area would melt faster, but the drink would stay cooler (until all the ice was gone).


- W



------------------------
Be seeing you.



Edited 1 time(s). Last edit at 02/25/2010 08:14PM by Winston.
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Re: I have balls made of ICE
Posted by: davester
Date: February 25, 2010 09:07PM
NOSXtasy was exactly right, which is why the cube melts and cools the fastest...it's a less efficient shape for keeping its cool so it gives its cool to the drink mucho pronto. No math required.

To the original poster, I recommend against using the thread title as a pickup line.



"In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion." (1987) -- Carl Sagan
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 09:26PM
Quote
davester
NOSXtasy was exactly right, which is why the cube melts and cools the fastest...it's a less efficient shape for keeping its cool so it gives its cool to the drink mucho pronto. No math required.


That's true for the initial cooling of the drink, but not once it reaches equilibrium (i.e. 32 degrees). If the point is to keep the drink "ice cold", then the shape of the ice doesn't really matter. If the point is to cool the drink as rapidly or slowly as possible, then it does matter.

Good advice on the pickup line.
:-)


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 09:32PM
Quote
Winston
If ice didn't cool by conversion of solid to liquid you'd be right. But ice doesn't primarily cool because it's cold, it cools from the phase change from solid to liquid. So the amount of melting is directly related to the heat transfer into the drink from outside.

Ice cools because of the temperature differential between the liquid and the ice. Phase change of the ice is merely a consequence of the ice absorbing heat from the liquid. If your theory regarding phase change were correct, pouring cold water into hot water would have no effect on the temperature of the hot water - the hot water would merely rise to the top and the cold water would sink to the bottom (which does happen to a slight degree, but over time the temperature of the system reaches equilibrium and is the same throughout the entire body of water).



It is what it is.



Edited 1 time(s). Last edit at 02/25/2010 09:45PM by N-OS X-tasy!.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 09:41PM
Quote
N-OS X-tasy!
Quote
Winston
If ice didn't cool by conversion of solid to liquid you'd be right. But ice doesn't primarily cool because it's cold, it cools from the phase change from solid to liquid. So the amount of melting is directly related to the heat transfer into the drink from outside.

Ice cools because of the temperature differential between the liquid and the ice. Phase change of the ice is merely a consequence of the ice absorbing heat from the liquid. If your theory were correct, pouring cold water into hot water would have no effect on the temperature of the hot water - the hot water would merely rise to the top and the cold water would sink to the bottom.

When ice converts from solid to liquid water, it absorbs heat in a non-linear way. I think this is called "heat of fusion"
[en.wikipedia.org]

Because of this water and ice can both exist at 32 degrees, and when heat is added to an ice/water mixture the mixture stays at 32 degrees until all the ice is converted to liquid.

Your hot water/cold water example has nothing to do with heat of fusion.


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 09:52PM
From the Wikipedia article. This describes freezing, but it works the same way when ice melts:

"When thermal energy is withdrawn from a liquid or solid, the temperature falls. When heat energy is added the temperature rises. However, at the transition point between solid and liquid (the melting point), extra energy is required (the heat of fusion). To go from liquid to solid, the molecules of a substance must become more ordered. For them to maintain the order of a solid, extra heat must be withdrawn. In the other direction, to create the disorder from the solid crystal to liquid, extra heat must be added.

The heat of fusion can be observed by measuring the temperature of water as it freezes. If a closed container of room temperature water is plunged into a very cold environment (say -20 °C), the temperature will be observed to fall steadily until it drops just below the freezing point (0 °C). The temperature then rebounds and holds steady while the water crystallizes. Once completely frozen, the temperature will fall steadily again.

The temperature stops falling at (or just below) the freezing point due to the heat of fusion. The energy of the heat of fusion must be withdrawn (the liquid must turn to solid) before the temperature can continue to fall."


So basically an ice/water mixture stays at freezing until all the ice melts. The rate of melting is determined by the amount of heat which can be absorbed, which depends on the "all else equal" factors mentioned above (air temperature, thickness of glass, etc.) It does not depend on the shape of the ice.


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 10:07PM
Quote
Winston
When ice converts from solid to liquid water, it absorbs heat in a non-linear way. I think this is called "heat of fusion"
[en.wikipedia.org]

Because of this water and ice can both exist at 32 degrees, and when heat is added to an ice/water mixture the mixture stays at 32 degrees until all the ice is converted to liquid.

Your hot water/cold water example has nothing to do with heat of fusion.

I didn't say it did, nor do I dispute your statement regarding heat of fusion. I DO dispute your statement that ice cools because of its phase shift to water - this is not true. In fact, you are in agreement with me - you clearly state above that the the ice/water mixture stays at 32 degrees until all the ice has been converted to water. If the temperature of the ice/water mixture doesn't change during the ice's phase change to water, then by definition no cooling is taking place during the phase change!

Of course, your statement above only applies to a very specific scenario - the one in which the ice/water mixture is already at 32 degrees and heat is applied to the ice/water system from an source external to that system. In a more typical scenario - one, say, where ice is used to cool a glass of warm water - the ice undergoes phase change to water continuously as it cools the water. Again, this phase change is a consequence of the ice absorbing heat from the water, not the cause of it. Clearly the temperature of the water exceeds 32 degrees in this scenario; thus, your statement "when heat is added to an ice/water mixture the mixture stays at 32 degrees until all the ice is converted to liquid" is inaccurate. It's much more accurate to say "when heat is added to an ice/water mixture the temperature at the boundary layer between the ice and the water stays at 32 degrees until all the ice is converted to liquid."

Ice cools a liquid because it is colder than the liquid in which it is submerged and for no other reason.



It is what it is.
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Re: I have balls made of ICE
Posted by: vitus
Date: February 25, 2010 10:16PM
Given that one would expect ice to be provided at temperature somewhat colder than the freezing point of water, (Home freezers typically run at about 0 deg F.) then one must consider thermal conductivity within the chunks of ice and the impact of this on when or if thermal equilibrium (homogeneity?) is ever actually achieved. Furthermore, thermal gradients within the fluid water also must be considered. The differences are small, but in this case the details are important.
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 10:22PM
Winston, everything you've quoted from Wikipedia is correct - it's your interpretation that is incorrect.

- Ice cools water because the ice is colder than the water; the ice absorbs heat from the water, cooling it in the process.

- The ice melts as it cools the water because in absorbing heat from the water the temperature of the outer layer of the ice rises to the point that it can not remain as a solid.

- The rate at which the ice can absorb heat from the water (and thus cool the water) is directly proportional to the surface area of the ice. That means that, all other factors remaining static, as the surface area of the ice increases the rate at which it absorbs heat from the water increases, which in turn increase the rate of phase change i.e. the rate of melting.



It is what it is.



Edited 3 time(s). Last edit at 02/25/2010 10:43PM by N-OS X-tasy!.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 10:37PM
Quote
N-OS X-tasy!

I didn't say it did, nor do I dispute your statement regarding heat of fusion. I DO dispute your statement that ice cools because of its phase shift to water - this is not true.

Sorry, but that doesn't make any sense to me. It sounds like you mean that heat is not absorbed by the phase change, which it is.


Quote

In fact, you are in agreement with me - you clearly state above that the the ice/water mixture stays at 32 degrees until all the ice has been converted to water. If the temperature of the ice/water mixture doesn't change during the ice's phase change to water, then by definition no cooling is taking place during the phase change!

That's only true if you define "cooling" as lowering temperature, not absorbing heat. In the absence of ice the temperature of 32 degree water will rise if the surrounding temperature is higher. I don't think it's accurate to say that having ice keep water at 32 degrees is not cooling it.


Quote

Of course, your statement above only applies to a very specific scenario - the one in which the ice/water mixture is already at 32 degrees and heat is applied to the ice/water system from an source external to that system. In a more typical scenario - one, say, where ice is used to cool a glass of warm water - the ice undergoes phase change to water continuously as it cools the water. Again, this phase change is a consequence of the ice absorbing heat from the water, not the cause of it. Clearly the temperature of the water exceeds 32 degrees in this scenario; thus, your statement "when heat is added to an ice/water mixture the mixture stays at 32 degrees until all the ice is converted to liquid" is inaccurate. It's much more accurate to say "when heat is added to an ice/water mixture the temperature at the boundary layer between the ice and the water stays at 32 degrees until all the ice is converted to liquid."

Ice cools a liquid because it is colder than the liquid in which it is submerged and for no other reason.

That's not what the Wikipedia article says, and not what I was taught in physics. You don't have to believe me, but do some googling on "heat of fusion". I think it's a pretty well accepted concept. I may be wrong about the water staying at exactly 32 degrees, but it does stay at a stable temperature right about 32 degrees until all the ice melts.

Re-read the Wikipedia description I quoted: the ice requires extra heat to convert from solid to liquid. As a result, the temperature of the ice and water both stay at the same point until all the ice melts.


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 10:44PM
Winston, the disconnect here is that you are describing the behavior of a system at one very specific, very unique set of conditions while I am describing the general behavior of the same system under a wide range of conditions. Technically we're both correct in our descriptions; however, your description does not address the original question "Does surface area affect rate of melting" because you have described a system in which, by definition, melting can not occur (assuming the ice/water mixture is a closed system).

Can we agree on that?



It is what it is.
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 10:47PM
Quote
Winston
That's only true if you define "cooling" as lowering temperature, not absorbing heat.

You're kidding, right?



It is what it is.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 10:49PM
Quote
N-OS X-tasy!
Winston, everything you've quoted from Wikipedia is correct - it's your interpretation that is incorrect.

- Ice cools water because the ice is colder than the water; the ice absorbs heat from the water, cooling it in the process.

- The ice melts as it cools the water because in absorbing heat from the water the temperature of the outer layer of the ice rises to the point that it can not remain as a solid.

No, that's not how heat of fusion works. The ice melts at 32 degrees into 32 degree water, absorbing heat in the phase change from solid to liquid. It does not change temperature while it goes through the phase change.


Quote

- The rate at which the ice can absorb heat from the water (and thus cool the water) is directly proportional to the surface area of the ice. That means that, all other factors remaining static, as the surface area of the ice increases the rate at which it absorbs heat from the water increases, which in turn increase the rate of phase change i.e. the rate of melting.

That's only true if the water has not already been cooled to 32 degrees. I think I've been clear that I am talking about a glass where the ice has already cooled the drink down. Once the drink is cooled, the surface area of the ice doesn't make any difference - its the "all else equal" factors which matter - i.e. how much heat is being transferred into the glass from the surroundings. The ice can't melt any faster than the amount of heat transferred from the surroundings.

I already acknowledged that ice with more surface area will do the initial cooling of a drink more quickly.


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 10:53PM
Quote
N-OS X-tasy!
Quote
Winston
That's only true if you define "cooling" as lowering temperature, not absorbing heat.

You're kidding, right?

No, I'm not. Most people consider air conditioning which keeps their home at a (relatively) constant temperature to be "cooling" their homes. I've noticed that thermostats even use the word "cool". And ones which work both directions are called "heat pumps".

By your reasoning something which is absorbing heat is not cooling.


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 10:56PM
Quote
N-OS X-tasy!
Winston, the disconnect here is that you are describing the behavior of a system at one very specific, very unique set of conditions while I am describing the general behavior of the same system under a wide range of conditions. Technically we're both correct in our descriptions; however, your description does not address the original question "Does surface area affect rate of melting" because you have described a system in which, by definition, melting can not occur (assuming the ice/water mixture is a closed system).

Can we agree on that?


No. I don't even understand what you mean by saying I described a system where melting cannot occur. You are refusing the accepted understanding of how heat of fusion works.


- W



------------------------
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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 25, 2010 11:01PM
Quote
Winston
That's only true if the water has not already been cooled to 32 degrees. I think I've been clear that I am talking about a glass where the ice has already cooled the drink down.

Yes, I acknowledge that above.



It is what it is.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 25, 2010 11:01PM
Quote
vitus
Given that one would expect ice to be provided at temperature somewhat colder than the freezing point of water, (Home freezers typically run at about 0 deg F.) then one must consider thermal conductivity within the chunks of ice and the impact of this on when or if thermal equilibrium (homogeneity?) is ever actually achieved. Furthermore, thermal gradients within the fluid water also must be considered. The differences are small, but in this case the details are important.

I agree that there are some fluid dynamic and self-insulation issues at the margins. But I think the basic concept of how heat of fusion works applies. Also, because ice floats and cold water sinks, drinks with ice in them "self mix" as the ice melts. This tends to keep the drink at a constant temperature throughout.


- W



------------------------
Be seeing you.
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Re: I have balls made of ICE
Posted by: guitarist
Date: February 25, 2010 11:52PM
I want to see this same discussion...this spirited, informed discussion...But with a key variable changed. A different circumstance.

Everybody here, completely drunk.

I want to see this discussion again, after ten shots of whiskey.

A round for the house! Bartender! Keep it coming!
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Re: I have balls made of ICE
Posted by: vitus
Date: February 26, 2010 07:41AM
Quote
Winston
Quote
vitus
Given that one would expect ice to be provided at temperature somewhat colder than the freezing point of water, (Home freezers typically run at about 0 deg F.) then one must consider thermal conductivity within the chunks of ice and the impact of this on when or if thermal equilibrium (homogeneity?) is ever actually achieved. Furthermore, thermal gradients within the fluid water also must be considered. The differences are small, but in this case the details are important.

I agree that there are some fluid dynamic and self-insulation issues at the margins. But I think the basic concept of how heat of fusion works applies. Also, because ice floats and cold water sinks, drinks with ice in them "self mix" as the ice melts. This tends to keep the drink at a constant temperature throughout.


- W

It may or may not surprise you to know that water is at maximum density at 4 deg C (about 39 deg F) therefore density gradients will enforce temperature gradients. The dynamics are essential.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 26, 2010 10:16AM
Quote
vitus
It may or may not surprise you to know that water is at maximum density at 4 deg C (about 39 deg F) therefore density gradients will enforce temperature gradients. The dynamics are essential.

Yes, and it also matters if the drink is being moved around or stirred (which would be the case with a typical bar drink). But if two drinks with identical amounts of liquid, identical containers, and the same amount of ice only differ by the surface area of the ice, will there be much difference in how fast the ice melts? It probably varies some by the ratio of ice to liquid (more room for convection with a lower ice to water ratio) and where the heat gain is in the container. But I'd guess that for working purposes the effects are small (i.e. I think you'd get similar density and temperature gradients regardless of the surface area of the ice).

I'm tempted to do an experiment.


- W



------------------------
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Re: I have balls made of ICE
Posted by: Diana
Date: February 26, 2010 03:37PM
Gentlemen,

I am not a physicist, and I remember a little something of the physical chemistry classes I had to take.

If I understand the problem correctly, the dissent appears to be a matter of whether you look at the problem as being a closed system or an open system, where a closed system does not allow for any exchange of energy with its surrounds and an open system does. The closed system is much easier to explain, and thus is normally discussed in undergraduate physics and physical chemistry courses. The reality is that very few systems are closed. The other part of the problem seems to reside in the ideas of "hot," "cold," and "heat." For the purposes of my contribution, I'll say that energy, in the form we perceive as heat, will move from one place to another. We also must look at what is releasing the energy, and what is absorbing the energy (define the system, and define the environment).

As far as whether or not ice "absorbs heat"--it will absorb energy from its environment as it goes through the process of the phase transition from a solid to a liquid. The energy goes into each individual molecule of solid water (ice) until they become energetic enough to overcome the forces holding them in the ice crystal matrix; when this happens, the molecule changes to the liquid phase. The TEMPERATURE of the system remains static until all the molecules in the matrix are in the liquid phase, and then the system absorbs energy again until it reaches the same temperature as its environment. This energy has to come from somewhere, namely the environment the ice is located. So yes, the ice will cool the water because it is absorbing energy in the form of heat as it melts. The ice is "warming" while the drink is "cooling." The ice and the drink will still be perceived by us as cold or cool until it absorbs enough heat to become a liquid at body temperature; above that temperature, the water is perceived by us as hot. In a closed system, the system is just the ice and the drink; it can include other things as you specify the size of the system and at the boundaries of said system, the energy transfer ceases to occur. The real world however is an open system, and energy transfer comes from many different places with no true boundaries.

Winston, the drink will not be at a constant temperature, as without physical mixing the transfer of heat from the warmer outside edges of the glass to the cooler regions next to the ice depend on diffusional processes, which in themselves are slow across such relatively large distances.

The discussion concerning whether or not the SHAPE of the ice makes a difference is similar, in that the heat from the edges of the ice must make its slow way towards the center of the mass of the ice (the cold takes a while to get to the outside edges of the ice, if you will). It is slowed because the heat is absorbed by the outside edge molecules, and is somewhat "lost" as these molecules are released from the matrix. The energy continues to work its slow way towards the center of the mass until all of the mass becomes the temperature of its environment, and has thus all the ice has melted into liquid water. The more surface area, the more area for the absorption of heat to occur, so YES, the shape of the mass of ice makes a difference. It will melt faster since it has more surface area; it will "cool" the drink faster because it has more surface area for the transfer of energy to occur.

In order to do the experiment that Winston is contemplating, I propose that you use two set-ups, one with one large chunk of ice (preferably round balls of ICE wink smiley ), and the other using the same mass of ice but the ice is crushed. Use the same thermometer for both experiments; the bar where you perform said experiments must remain at or near the same temperature for both experiments since it is the drink's "environment." The only thing different in the two set-ups will be the shape of the ice. A time vs. temperature curve will tell you a lot about the state the system is in and how long it takes for it to change. When the system reaches thermal equilibrium with the temperature of the bar, the experiment is over. NO MIXING IS ALLOWED, and don't drink it! If you are curious about thermal gradients, use two thermometers: one near the ice, and one near the outside edge of the glass (but still in the drink).

Your buddy times it, you measure it, and you both have a few while you are working. Let us know how it goes.

And to clarify, ice floats because the density of water does decrease as it cools (gives up energy) and goes through the freezing process; the density of water becomes greatest just before freezing. The freezing process causes the solid water to expand as the molecules rearrange themselves from a random chaotic order to a (somewhat) crystalline one for water. As the temperature continues to fall, the ice will undergo several more phase changes as the molecules spontaneously rearrange themselves. The thermal gradients caused by the melting of ice and and freezing of water are quite real, and become more apparent the larger the body of water. Go swimming sometime in your local body of water (not a pool!) and check it out.

Diana

I am not a physicist, nor a physical chemist, but an analytical one. I hope this helps.



Edited 1 time(s). Last edit at 02/26/2010 03:37PM by Diana.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 26, 2010 06:06PM
Quote
Diana
Gentlemen,

The discussion concerning whether or not the SHAPE of the ice makes a difference is similar, in that the heat from the edges of the ice must make its slow way towards the center of the mass of the ice (the cold takes a while to get to the outside edges of the ice, if you will). It is slowed because the heat is absorbed by the outside edge molecules, and is somewhat "lost" as these molecules are released from the matrix. The energy continues to work its slow way towards the center of the mass until all of the mass becomes the temperature of its environment, and has thus all the ice has melted into liquid water. The more surface area, the more area for the absorption of heat to occur, so YES, the shape of the mass of ice makes a difference. It will melt faster since it has more surface area; it will "cool" the drink faster because it has more surface area for the transfer of energy to occur.

Thanks for your comments. However, if the ice/water mixture stays at approximately 32 degrees while the ice melts, then the temperature differential between the mixture and the environment around it will stay the same. (I am ignoring that as the ice melts the differential will vary more around the glass - let's assume I am looking at a relatively short period of time. If the analysis holds for one short period of time, then you can string together short periods to generalize.)

Given a fixed temperature differential and a specific container (the glass) there will be a fixed rate of heat (energy) transfer from the environment into the glass. As long as there is enough ice to maintain the differential, wouldn't the amount of heat (energy) absorbed by the mixture remain constant? (Again, I am ignoring that this would change as more ice becomes liquid.) If a fixed amount of heat per time period is entering the glass, and there is enough ice to hold the temperature, I can't see how any more ice would melt than the amount needed to maintain the temperature. Given that there is enough ice, the shape of the ice would therefore not matter.


- W



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Re: I have balls made of ICE
Posted by: vitus
Date: February 26, 2010 09:45PM
Thanks to Diana for an excellent introduction.

Here's a layman's description of a solution to the question at hand. The coldest water will be directly next to the ice. All the other water is warmer depending on its position relative to the container walls and the closest chunk(s) of ice. How quickly heat enters the container depends on the temperature differential between the water and the surroundings. More cold water near the container boundaries means more rapid heat flow into the container. You get more cold water next to the container boundaries by distributing the cold water as much as possible. You distribute the cold water as much as possible by distributing the ice as much as possible. Ergo the ice with the greater surface ares melts more quickly.

More detailed explanation requires an understanding of solutions to Fourier's Law of Heat Conduction in 3D.

Oh, there should be some discussion of thermal transport within the ice as well, but that only reinforces the above conclusions. The core of the ice is colder than the surface of the ice. Transportation of heat to the core of the smaller ice chunks is faster as opposed to a single large chunk because of the surface to volume ratio and just plain geometry.
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Re: I have balls made of ICE
Posted by: Winston
Date: February 26, 2010 11:14PM
OK, vitus's description makes sense to me. As I think about it, I don't think I have been giving enough credit to the temperature differential across the drink. If ice with greater surface area keeps the edges of the glass cooler, then it would melt faster because of the larger temperature differential between the glass and the surroundings. But it would also be keeping the drink colder overall.

The other effect I'd thought of is that ice with a larger surface area would cool the drink faster initially, increasing the temperature differential sooner. This would also cause it to melt more quickly.

I'd still like to test it if I can find an ice tray to make different sized cubes to see if it makes any practical difference.


- W



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Re: I have balls made of ICE
Posted by: Diana
Date: February 27, 2010 11:13AM
Quote
Winston

I'd still like to test it if I can find an ice tray to make different sized cubes to see if it makes any practical difference.


- W

Just make sure that your thermometer is able to read to about the hundredths of a degree. When we do a similar experiment during the semester (obtaining the molar mass of a substance via the freezing point of its solutions) we would use a thermometer reading to 0.02 degrees C. PM me if/when you are ready to investigate!

Diana
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Re: I have balls made of ICE
Posted by: Winston
Date: February 27, 2010 02:57PM
Quote
Diana
Quote
Winston

I'd still like to test it if I can find an ice tray to make different sized cubes to see if it makes any practical difference.


- W

Just make sure that your thermometer is able to read to about the hundredths of a degree. When we do a similar experiment during the semester (obtaining the molar mass of a substance via the freezing point of its solutions) we would use a thermometer reading to 0.02 degrees C. PM me if/when you are ready to investigate!

Diana

That'd be great if I had a thermometer (actually, two of them) like that. I plan to just see how long it takes the ice to melt.

:-)


- W



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Re: I have balls made of ICE
Posted by: N-OS X-tasy!
Date: February 27, 2010 10:36PM
Quote
vitus
Thanks to Diana for an excellent introduction.

Agreed. Bravo, Diana!


Quote
vitus
More detailed explanation requires an understanding of solutions to Fourier's Law of Heat Conduction in 3D.

A review of Fourier's Law will in fact show that heat flow into the cube is directly proportional to the surface area of the ice; I referenced my old heat transfer text to confirm this during my participation in the thread Thursday night. As long as there is actual heat flow into the ice - as there definitely is in the system under discussion - it will vary in a manner directly proportional to the surface area of the ice.



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