Grade 7 Heat project

[NeedsHelpiNScience]

I'm doing a heat project in school and your supposed to use household items to wrap around a water bottle and when the day comes my teacher is gonna put boil water and see if it can work and hes gonna time how long it can go. the items im using is some ultra cloth tin foil and a large Bristol board to put around it and im wondering if that will work and if i can get Styrofoam like which kind do i use the plastic cup one of the ones to keep something like a TV from breaking?

[timo]

You know,

my teacher is gonna put boil water and see if it can work and hes gonna time how long it can go.

is not a very exact explanation of what you are supposed to do. Are you supposed to insulate the water bottle, as in "my teacher will fill the bottle with boiling water and time how long the water stays hot", perhaps? Since non-moving air is an excellent insulator, Styrofoam should indeed work quite well for insulation.

 

Oh, and please at least try to use proper grammar and spelling when asking other people for help or a favor (I'm assuming English is your native language, here). With a little effort it's not that hard to learn, and making the impression of someone that cannot even read and write is not cool in the long run.

Edited April 10, 2012 by timo

[Mosheh Thezion]

Well.. we can only presume, you mean to insulate a bottle... in which case... yes... wrap in foil, and use as thick layer of foam as possible.

However... you should... want to remove all air gaps.... i.e.. make the bottle fit.. as snugly.. perfectly.. into the styofoam as possible,... thick foam...

a big block... with a exact hole cut out...

probably... cut a cube... as large as the bottle... then cut it in half... and carve out the two halves of the cavity... which you would put the bottle in.

test it.. over and over.. as you cut out foam.. to get it to fit as perfectly as possible.. and then... tape it shut when it fits good.

 

I.. would wrap it in aluminum foil... and then make the box of foam... and then.. tape over it.. with say... plastic packing tape... the goal being to prevent any air which is between the foam and the bottom, or foil... from rising out... tape up the top... as that will hold in the air.... as rising air.. will cause loss.

(Do not cover the top openning of the bottle.. obviously... just wrap it well... so no air can escape.)

 

also.. do not forget the bottom... and top... both can allow heat loss....

 

If this... is your project... then.. the thicker the foam.. the better.. but anything more than 3 inches would be a waste probably....

the real thing.. is preventing air.. from escaping... and then cover the top with a foam cap... to keep the cap from leaking heat.

 

I wouldnt use the bristol board... I'd stick with foil or mylar... and thick styro foam.

 

I wish I was in the 7th grade... I would be a much better student than I was then...

 

By the way... you may want to read this... http://mosheh.org/Education.html

the study method you use... will have a great effect on how well you do... and how far you can go...

 

 

-Mosheh Thezion

[Schrödinger's hat]

Foil only makes sense if you have already reduced conduction and convection.

It's best to break the problem down into (and prioritize it with respect to) three categories.

 

Conduction:

Make sure it's not in direct contact with anything that conducts heat well. Low density, non-metallic substances (ie. air) work extremely well.

Convection:

If part of a fluid moves after it heats up, it can be replaced with another part at a lower temperature. This speeds up conduction greatly.

This is the reason things like foam are good insulators -- although they conduct more readily than air, they significantly reduce or completely stop convection.

Foam is generally better at insulating the lighter it is (and thus less better-than-air-conducting solid there is in it) along with being better if it has smaller pockets of air. The material does make some difference but is not as important.

 

Conduction and convection are by far the most significant at moderate temperature differences, but if you have already controlled for these as well as you can, there is one more factor:

 

Radiation:

Even in a complete vacuum (no conduction and thus no convection either) objects will still lose heat to their environment by emitting heat in the form of light (at low temperatures mostly in the infrared range).

If you can somehow place a reflector (such as aluminium foil) in the path of this light in a place where it will not be as hot as the source (ie. have a transparent insulator, ideally air or vacuum between the hot thing and the foil) this light will be reflected back into the object and (some of it will be) reabsorbed.

 

Given this, and the household materials constraint I'd build something like this:

If the shape of the bottle is controllable, make it as close to spherical -- or at least same height as width -- as possible, lower surface area to volume ratio means less opportunity for heat transfer. Also, bigger is better in this regard.

 

Bottle -> thin to medium layer of foam with holes in it (ie. just enough foam to support the foil whilst leaving as much of the intervening space empty) or foam webbing (like that used for fruit packing) -> foil -> thick layer of foam

 

Optionally a second layer of foil just over the bottle but under the foam might help (or might hinder).

 

NB: use the smallest/thinnest amount of foil that does the trick, you don't want the region just around the bottle to have a high heat capacity.

 

Pay special attention to the lid/opening to make sure air can't travel in or out.

 

Also re. contact with the thick layer of foam, you want a close fit (to avoid convecting heat to a larger region of foam), but not a tight/smooth fit. Bumps and dents (the smaller but more numerous the better) on the contacting surface are good because they reduce contact area -- as long as they aren't big enough to encourage convection.

 

One other note, if you have a supplied bottle or difficulty making the opening as good as the rest of it, you may be better off having a lid/plug of foam coated in foil/other opening on the bottom (with toothpicks or something to support the weight of the bottle and stop good contact) as hot fluid tends to rise.

 

Final thought: If it needs to be opened regularly to check the temperature you might consider putting a separate, much smaller lid/openable hole for that purpose

Edited April 10, 2012 by Schrödinger's hat