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Author Topic: Hand Warmers !...how do they work ?  (Read 17733 times)

neilep

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Hand Warmers !...how do they work ?
« on: 22/08/2007 12:54:44 »
Hi There,

I'm Neil...I think this site is great...I hope to get to know you all !


You see this hand warmer :




How does it work ?....you press a button and VOILA !..a sort of crystal thing happens that spreads amongst it and then it gets warm !!

You can then do it again and again !


I used to keep my hands warm another way but I got arrested ! ;)

So, what are the compounds and what is the reaction that's happening in the hand warmer ?

Thanks

Neil
xxxx


Karen W.

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Hand Warmers !...how do they work ?
« Reply #1 on: 22/08/2007 14:34:41 »
LOL LOL.. I wonder if it works on the same lines as those new fangled ice packs where you disturb the pack by smacking it against a counter or hard surface and its being broken apart starts some kind of reaction which gets really cold for quite a good amount of time?

I have never used a hand warmer other then mittens pockets or between my thighs...LOL

I do however know that my boys and their hunting buddies have used them on occasion.. It confuses me although at one point I remember hearing why, but I can't remember... Good Question..

paul.fr

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Hand Warmers !...how do they work ?
« Reply #2 on: 22/08/2007 16:23:37 »
I think this was once a question on TNS, any way. i see that it is one of the reusable ones - there are a few types.

The reusable ones generate heat through exothermic crystallisation of supercooled molten materials (usually sodium acetate) and are reusable. These can be recharged by boiling the warmers and allowing them to cool. Heating of the pads is triggered by snapping a small metal device buried in the pad which generates shock waves to initiate crystallisation.

Karen W.

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Hand Warmers !...how do they work ?
« Reply #3 on: 22/08/2007 16:25:20 »
Wow thats cool!

neilep

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« Reply #4 on: 22/08/2007 16:32:10 »
THANK YOU VERY MUCH PAUL AND KAREN

But what does ' exothermic ' mean ?...and when you say they are supercooled what does that mean also ?....do they take some stuff (sodium acetate..*what ever that is *) and whack it in a big freezer ?

paul.fr

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Hand Warmers !...how do they work ?
« Reply #5 on: 22/08/2007 16:39:51 »
THANK YOU VERY MUCH PAUL AND KAREN

But what does ' exothermic ' mean ?...and when you say they are supercooled what does that mean also ?....do they take some stuff (sodium acetate..*what ever that is *) and whack it in a big freezer ?

oh dear, i have only been awake half an hour. but i will have a go.

exothermic reactions are when the energy you need to produce a reaction is less than the energy that the reaction provides, thus giving heat, or energy in the form of. may be slightly out but someone will correct me.

no more question until i have had some coffee, too many questions in such a short space of time.

i will give you the answer i give Anastasia when she asks too many questions at once. "because it is"


neilep

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Hand Warmers !...how do they work ?
« Reply #6 on: 22/08/2007 16:50:12 »
THANK YOU VERY MUCH PAUL AND KAREN

But what does ' exothermic ' mean ?...and when you say they are supercooled what does that mean also ?....do they take some stuff (sodium acetate..*what ever that is *) and whack it in a big freezer ?

oh dear, i have only been awake half an hour. but i will have a go.

exothermic reactions are when the energy you need to produce a reaction is less than the energy that the reaction provides, thus giving heat, or energy in the form of. may be slightly out but someone will correct me.

no more question until i have had some coffee, too many questions in such a short space of time.

i will give you the answer i give Anastasia when she asks too many questions at once. "because it is"



WOW !!...exothermic reactions are pretty cool/hot !...so any kind of munition going off must also be exothermic.....thanks Paul.....grab a coffee before Eth drinks the worlds supply !!


paul.fr

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Hand Warmers !...how do they work ?
« Reply #7 on: 22/08/2007 17:52:48 »
I think Dave did a kitchen science on hand warmers, but i have searched and can't find it!

neilep

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« Reply #8 on: 22/08/2007 17:54:26 »
I think Dave did a kitchen science on hand warmers, but i have searched and can't find it!

I've hinted a few times at the wonder that is our beloved search engine !

paul.fr

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Hand Warmers !...how do they work ?
« Reply #9 on: 22/08/2007 17:57:51 »
I think Dave did a kitchen science on hand warmers, but i have searched and can't find it!

I've hinted a few times at the wonder that is our beloved search engine !

It's not the search engine - http://www.thenakedscientists.com/HTML/podcasts/2003-2004/show/2006.11.19/ gives the show where the experiment was done. I just can't find the experiment.

neilep

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« Reply #10 on: 22/08/2007 18:03:55 »
I retract my statement...the search engine is fab !!

Thanks for the link Mr Paul.

Lee Cronin

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Hand Warmers !...how do they work ?
« Reply #11 on: 28/08/2007 21:42:01 »
Hand warmers work since there are a super saturated solution of a simple salt - sodium thiosulphate or something similar.  Flicking the metal disc provides a nucleation site for the sodium salt to start to crystallise which it does very rapidly and the crystallisation is highly exothermic i.e. it gives out heat. To prepare the warmer for another session is easy.  You just place it in a saucepan and heat it in water until the salt redisssolves.  This is an endothermic process - i.e. it needs heat.

The neat thing is that this device can be used over and over - the process that is occuring is totally reversible.

I hope this helps.

Lee

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Hand Warmers !...how do they work ?
« Reply #12 on: 30/08/2007 09:34:33 »

I think Dave did a kitchen science on hand warmers, but i have searched and can't find it!

I did, but I don't think I have written it up yet, I have concentrated on the ones you can do at home.

I've hinted a few times at the wonder that is our beloved search engine !
Yeeerrrrs, there are a couple of different types of search engine the one at the bottom of the kitchen science etc works ok, the main one I just got from a module somewhere and it isn't very good. I will write my own soon.

 

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