Keep an ice cube from melting

March 17, 2007 6:06 AM

SchoolProjectFilter: Help my son keep an ice cube from melting!

The mission: to design a container that will keep an ice cube from melting completely for at least 4 hours. (It can melt a little, but needs to stay as un-melted as possible.)

They can use common household products such as:
- paper products
- cotton
- fabric
- clay
- foam
- wax
- foil
- sandpaper
- plastic wrap

What's our best shot?

posted by I_Love_Bananas to sports, hobbies, & recreation (13 answers total)

Styrofoam, I believe.

Cockeyed Test.

You might get bonus points for using Rice Krispie treats.
posted by cobaltnine at 6:18 AM on March 17, 2007

Put salt in water, wrap it within a container of clay, followed by wax, foil and cotton wrapped in fabric. Put the ice inside that.
posted by markesh at 6:30 AM on March 17, 2007

Actually I think my kids benefitted by my 'help' with their projects. Kids learn all the time, you can't stop it, only expose them to better things to learn. To a kid, helping Dad solve a problem is more enlightening than struggling for a solution alone.
Besides, it sucks to be the one kid in your class who didn't get parental help and your project looks weak by comparison.

I, too, would guess Styrofoam, as suggested by Cockeyed Test, has the highest R-factor on that list. The bigger the block of foam, the tighter the seal, the longer ice stays cold.
posted by dkippe at 7:09 AM on March 17, 2007

Freezer packs and more ice! (well you said common household items)
posted by FreezBoy at 7:28 AM on March 17, 2007

i dissent from styrofoam. cotton balls are more compressible and just as good "r". wrap the ice cube tightly in cotton balls, then surround that with aluminum foil. shiny things don't heat up as fast as dark things. oh, and one more thing...
the initial temperature of the ice cube is an uncontrolled variable, so chill it as much as you can before the test (use dry ice to do this, if you have it). heck, i'd use liquid nitrogen if i had it.
posted by bruce at 7:51 AM on March 17, 2007

I appreciate genuine responses that will give me real information I can use to guide our efforts.

Here's how to bring the complainers together with the answers--what you can give your youngster here is process, and let him do the brainstorming. Suggest that he carefully measure each effort by detailing exactly what he did each time and find a way to measure your efforts in terms of melting. Giving him some sort of 1 2 3 out of the box solution defeats the purpose of the assignment, which is not to teach the future citizens how to keep ice cold in a global warming Beyond Thunderdome Al Gore nightmare, but to teach them scientific method, which is to systematically approach the solving of problems to increase efficiency and effectiveness.
posted by Ironmouth at 8:13 AM on March 17, 2007

heck, i'd use liquid nitrogen if i had it.

Household items, bruce, household items.
posted by odinsdream at 8:28 AM on March 17, 2007

re: do it yourself

I hated these projects with a passion in high school. We had projects that took upwards of 20 or 30 hours to build a catapult, or make a device that lets a ball roll down a ramp for at least 30 seconds (think back and forth...). They taught nothing, but required massive amounts of work.

As for the project itself, I don't know when you can start the time trial, but if you have a way to do it, prime whatever the device is with cold. Even if you have a great insulator, if there is lots of heat inside it at the start time, that heat will screw up the ice cube. I think styrofoam is the best bet, since they have styrofoam coolers designed for practically this thing (keeping cold things cold).
posted by cschneid at 8:39 AM on March 17, 2007

Household items, bruce, household items.

You're obviously not a scientist. :-P


Be sure that the layer closest to the ice is something relatively waterproof. If the cold water is wicked away (by something like cotton) the ice cube may melt more quickly.

I had a science project as a kid where we took two identical coolers, filled them with ice, and drained the water off of one periodically. Turns out that draining all that cold water makes the temperature go way up (since you're replacing it with warm air).
posted by chrisamiller at 8:42 AM on March 17, 2007

Take your ice cube, and freeze it inside a larger block of ice. Carry to school in any container you like.

Caution: may result in law school degree.

If the teacher is smart, then you only build the contraption, and he/she provides the ice cube.

Seriously, this solution has already been given: inner container, as much insulation as possible, outer container.
posted by Ynoxas at 9:21 AM on March 17, 2007

I would make a box out of thick styrofoam, with an inner chamber measuring 3 ice cubes x 3 ice cubes x 3 ice cubes. Place 27 ice cubes in the container, with the center one being the subject of the experiment.
posted by rocket88 at 11:02 AM on March 17, 2007

Heat transfers by two mechanisms, radiant and conducted. You can add a third, convection, but that is just conduction with a circulating material.

In terms of conduction, vacuum is the best possible insulator, but air is the best insulator you've got.

The problem with air is that it tends to move with the tiniest inducement, which is why things like foam and fiberglass bats are used as insulation. Foam is just a little bit of plastic and a lot of air, fiberglass bats the same, except they are also fireproof. In either case, the material helps to restrict the air from moving around - no more convection.

What you need to do is find a way to create an air tight outer container, so that warm air can't leak into the insulation layer. Then have a thick layer that is mostly air, but where the air can't circulate due to obstruction. loose (not compressed!) cotton balls, or foam are good.

Then there is radiant transfer. To minimize that, you need to maximize reflectivity, so that incoming infra red radiation is reflected instead of absorbed by the apparatus. That is where wrapping in tinfoil comes in.

Chrisamiller is right about a water tight barrier. Letting the cold water flow away from the ice is basically the same as letting cold air flow away. They will both be replaced by warm air, bringing heat energy to the ice, bad. Except that the heat capacity of water is much higher than that of air, so relative to the ambient temperature you are losing a lot more.

How exactly you order this for maximum effect, I'm not sure.. For example, you could do ice, water tight barrier, insulation, air tight barrier, insulation, radiation barrier. With the same material you could go ice, water tight barrier, insulation x2, air tight barrier, radiation barrier.

Finally, no salt. That is a trick for cooling drinks faster in the presence of ice water. Ice water without salt will be at the freezing point, but salted water freezes at a lower temperature, so adding salt makes the material surrounding your pop cans colder than it would otherwise be. In this experiment, I can't see any benefit unless you are allowed to use a salt water bath, and a lot more ice (similar to the lawyerly "freeze your ice in a bigger block of ice" comment) - unlikely..
posted by Chuckles at 12:53 PM on March 17, 2007

If it was me I'd place the ice cube in a waterproof grip-seal bag and suspend it in a vacuum flask filled with a mixture of crushed ice and salt. All commonly-available household materials, and it may come out colder than when it went in.

This may be considered against the spirit of the competition, but then I'm a smartass, and I'd rather show off with a clever-clever solution than actually win.
posted by Leon at 3:49 PM on March 17, 2007 [1 favorite]