Building A Thermos out of household items

[cadeo]

Hi, I need to build a homemade thermos for my grade 7 heat project. I was thinking of using a plastic water bottle as the container, and then put cotton pads and tin foil around it. But I don't think that will suffice to keep it warm long enough. does anyone have suggestions. The project is due soon so please help.

 

 

 

NOTE: The Cotton pads will have "air pockets that will reduce convection,then I will wrap them in tape and attach the tinfoil so it will reduce radiation and the insulation I add will reduce conduction. Please correct me if i'm wrong.

[Phi for All]

Spacesuits worn by astronauts have multiple "sandwiched" layers. Perhaps you could use multiple tinfoil layers sandwiching something (plastic wrap? paper?) that keeps the metal layers from touching each other to reduce heat transfer.

[cadeo]

I was planning to do something similar like that, use saran wrap between the layers of insulation and tinfoil to stop heat transfer, I will use a plastic water bottle as my container I guess

[michel123456]

Hi, I need to build a homemade thermos for my grade 7 heat project. I was thinking of using a plastic water bottle as the container, and then put cotton pads and tin foil around it. But I don't think that will suffice to keep it warm long enough. does anyone have suggestions. The project is due soon so please help.

 

 

 

NOTE: The Cotton pads will have "air pockets that will reduce convection,then I will wrap them in tape and attach the tinfoil so it will reduce radiation and the insulation I add will reduce conduction. Please correct me if i'm wrong.

 

Sounds good, as long as you don't wrap too tightly. As you said, the air will do the job. Instead of cotton you could use cheaper toilet paper. The main problem will be the external structure. A thermos bottle is in fact a bottle inside a bottle, the 2 bottles join near the closing cap. You could use a small plastic bottle inside a large one that you have cut in the middle then taped together. Something like that. But you will need something to secure the inside bottle in position, because when you will fill it with liquid, it will become heavy and may very easily get out of place.

 

(edit)

IIRC in a regular thermos, the inside bottle is made of thin glass silvered, acting as a mirror from the inside to reflect radiation.

 

Also I suppose your teacher will test the bottles. Think how he will do the tests, will he put boiling water in order to discard all the plastic bottles of the class? will he turn the bottle upside down? will he measure temperature? how will he do that? will he throw the bottle down to test its resistance? Or is this only a conceptual exercise?

[Phi for All]

Also I suppose your teacher will test the bottles. Think how he will do the tests, will he put boiling water in order to discard all the plastic bottles of the class? will he turn the bottle upside down? will he measure temperature? how will he do that? will he throw the bottle down to test its resistance? Or is this only a conceptual exercise?

This is a very good point. What if the teacher puts hot water inside, measures the temperature, then puts the thermos in a refrigerator for a while to see how well it retains heat in a less than room temperature environment (this also reduces the time he would need to test the whole class, a clever thing teachers are known to do)? Perhaps a reflective layer of tinfoil closest to the bottle, a layer (or double layer) of toilet paper, tinfoil, toilet paper, tinfoil, toilet paper and tinfoil (the outer layer of tinfoil can also act as a radiant barrier against cold, right?).

[sean ginamionuy]

the cotton with rips will make more covection

[Acme]

Hi, I need to build a homemade thermos for my grade 7 heat project. I was thinking of using a plastic water bottle as the container, and then put cotton pads and tin foil around it. But I don't think that will suffice to keep it warm long enough. does anyone have suggestions. The project is due soon so please help.

 

NOTE: The Cotton pads will have "air pockets that will reduce convection, then I will wrap them in tape and attach the tinfoil so it will reduce radiation and the insulation I add will reduce conduction. Please correct me if I'm wrong.

'Thermos' is a brand name for a vacuum flask (aka Dewar flask). Insulating a bottle is technically just an insulated bottle, not a Thermos. If the assignment specifies 'Thermos', then you may want to get clarification.

[John Cuthber]

Foil is good. This stuff is better

https://en.wikipedia.org/wiki/Space_blanket

It's mainly plastic (rather than metal) so it is a much poorer conductor.

 

And, since nobody has a very good vacuum pump as a "household item" there's no way that the assignment can really mean a Thermos (or Dewar) flask.

The conductivity of low pressure air is (perhaps surprisingly) just as good as that of air at ordinary pressure . You need to drop the pressure to the point where the mean free path is larger than the separation between the inner and outer layers of glass.

Edited December 6, 2015 by John Cuthber

[Acme]

And, since nobody has a very good vacuum pump as a "household item" there's no way that the assignment can really mean a Thermos (or Dewar) flask. ...

Good being a relative term, one could attach some tubing to a certain style of squirt gun a 7^th grader may well have and draw a vacuum. Might be a problem keeping the outer bottle from collapsing if it's plastic.

 

Squirt gun