Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Quantum_Vaccuum on 25/09/2007 00:12:53
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In school we have a lab where i have to create a good insulator for an ice cube to make it last the longest under a heat lamp, I wanted to make a semi-vacuum to stop most of the heat from entering, sort of like a thermis, but i couldn't succeed in making one of those, can anyone give me another Idea, or a way of making my idea work?
And by the way, lets say i had a heat field around the ice cube that was lets say 10°C more than the outside temp. and found a way to make sure that that heat would not move at all, just stay put, not radiating, conducting, or any other method of exothermic reactions, could it possibly stop all other heat sources from entering?
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If you are putting it under a heat lamp, then the first thing you need to do is prevent radiation from the lamp getting to the ice cube (aluminium foil will do fine).
You don't want to put the ice cube in a vacuum, since the vacuum will itself cause the ice to sublime - you would want to put the ice in an airtight box, and put the box in the vacuum (but you also want to make sure that as far as possible there is no contact between the box inside and the outside - wether hang it on a thread, or better still, magnetic suspension).
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Good point, but I still don't understand how to make a good vacuum using home materials, and how would i magnetically suspend the box?
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Good point, but I still don't understand how to make a good vacuum using home materials, and how would i magnetically suspend the box?
A vacuum is the ideal, but you could have a lesser insulation simply by creating a foam lined box (the foam should stop convection, but will not stop conduction).
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so to stop everything all together, (the best i can) would be a box lined with foam, then to have aluminum foil around it?
P.S. I thought of maybe elevating the Ice cube a bit, so when it melts, it wouldn't interact with the hotter water, would that be of any use, or should i not bother?
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I would stick to making the inside of the box as small as possible so that you limit convection currents within the box (also to reduce the amount of warm air that might become trapped within the box).
I doubt that the water around the ice will be any warmer than the ice itself, and may even be a fraction cooler (as the ice melts, the ice/water will cool as it absorbs the energy needed to melt).
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[diagram=277_0] i=aluminum foil on the outside, ii=the foam iii=cube of ice iv= pizza table thing holding it up v=the melted water,
This is what i thought would be most like my project, but since reading yours i may change it, but i dont think the ice should touch the walls is this correct?
EDIT: why isn't the diagram appearing?
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It should not touch the outer wall, but the idea is that the insulation should be between the inner and outer wall, so I would not worry about it touching the inner wall (ideally made of a material with low thermal conduction, such as glass, or plastic).
The other thing I was thinking about is pumping some of the air out from between the inner and out boxes by using one of those devices used to remove air from half used wine bottles. Do this after you put the ice cube in the inner box. Not only will this reduce the amount of air in the box (and so reduce the opportunity for heat transfer - although it will be well short of being a vacuum), but the act of lowering the pressure within the box will probably reduce the temperature a bit (although this may be classed as active cooling rather than simply insulation).
Ofcourse, you could cheat by simply using a Thermos flask (which has a vacuum built in between the inner and outer wall, and is glass lined).
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kk, i just finished the project, and my idea was "the hut"
There is the main frame, which is a very small boxish shape of foam
Then there is at least 3 layers of aluminum foil all around the foam.
And I have some cardboard on the sides, which also raise it up from the blacktop which the "hut" will
be on during the experiment.
Also, i made a cap, which is cardboard surrounded by aluminum foil, and a big air bump in the middle to stop some heat from entering the start.
Then if allowed:
I have a big plastic plate shaped thing that can cover the whole "hut"
And also a white paper to put underneath so there is no heat to be absorb.
Tell me if you could think of anything to improve it,
Thx a lot for your help. =]
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Good point, but I still don't understand how to make a good vacuum using home materials, and how would i magnetically suspend the box?
how about putting it in a vacuum (thermos) flask? Here is a link to make one using kitchen equiptment.
http://www.thenakedscientists.com/forum/index.php?topic=6730.msg70800#msg70800
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How about some roofing shingles on the top? They are fairly good at keeping radiant heat out, aren't they?
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Suspending the ice cube above any surface would help a lot. Can you make your own ice cube? If so, make it with a thread running through the middle, then tie the ends of the thread to a support. If not, make or get some kind of mesh or net. The key is to get a low surface area for contact.
Dick
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Thanks a lot people, I'll try to incorporate most of your ideas, and i'll get back to you guys with the results tomorrow.
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worked really well lost two grams out of 19, when it was 80 degree outside, and it was out for 20 min, thx =]