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Hot fingers

 
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Wildlifewriter
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Joined: 04 Aug 2005
Posts: 948
Location: Norn Iron

PostPosted: Mon Dec 26, 2005 1:28 pm    Post subject: Hot fingers Reply with quote

I'll be the King of Bling at upland caches this winter, with the M&S re-useable handwarmers what Santa brung me for Christmas...



... the thing is: how do these work?

They are activated by clicking a little metal disk which is inside the liquid-filled pouch.(left) When this is done, some kind of chemical reaction (or it may be a physical phase change) takes place - the substance inside solidifies, and heats up to about 60C. (right)

After use, the handwarmers can be "recharged" (it says here) by boiling 'em in a pan of water for about 10 minutes.

Does anyone know the principle which is operating here? I'm mystified. Confused


-Wlw
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Karl60
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Joined: 26 Sep 2005
Posts: 8
Location: Perth and Kinross

PostPosted: Mon Dec 26, 2005 5:46 pm    Post subject: Hand Warmer Reply with quote

Googling hand-warmer and metal-disc will answer this question.
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Billy Twigger
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Joined: 30 Aug 2005
Posts: 352
Location: N55 51.686 W5 05.647

PostPosted: Mon Dec 26, 2005 7:41 pm    Post subject: Reply with quote

Judging by the size of Santa in your picture, these are huge!!! Are you sure that they are not underfloor heaters?
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wuthered
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Joined: 29 Aug 2005
Posts: 51
Location: Co Down

PostPosted: Tue Dec 27, 2005 12:24 am    Post subject: Reply with quote

I would urge that you use caution when leaving these to boil for 10 minutes. The wine bottle warmer that I did this with was forgotten about for a good while longer, leaving a saucepan which had boiled dry, covered with melted plastic and an unknown blend of chemicals. The house was filled with an acrid smell which lingered for days. It also left a rather harsh opinion that I should not be left unattended for longer than 10 minutes.
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Big Wolf
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Joined: 05 Sep 2005
Posts: 577
Location: Carnbroe, Scotland

PostPosted: Tue Dec 27, 2005 12:43 am    Post subject: Reply with quote

What is happening here is strange but can be understood if you think about water freezing. Water freezes at 0 C. If you were to stick a thermometer in a cup of water and put the cup in the freezer, you would find that the temperature of the water falls to 0 C and then hangs there until all of the water is completely frozen. Then the temperature of the then solid water falls to the temperature of the freezer.

What if you could somehow supercool the water? That is, say that you could get the water's temperature to 10 degrees below freezing without it crystallizing into a solid (you can sometime do this using a very clean glass and distilled water so there are no points for the water to begin crystallizing). In this condition you can tap the glass and the temperature of the water will jump up to 0 C and the water will solidify quickly.

The magic heat packs usually sodium acetate and water. It turns out that sodium acetate is very good at supercooling. It "freezes" at 54 C, but it is happy to exist as a liquid at a much lower temperature and is extremely stable. Clicking the disk, however, has the ability to force a few molecules to flip to the solid state, and the rest of the liquid then rushes to solidify as well. The temperature of the solidifying liquid jumps up to 54 C in the process.

When you boil the solid you melt it back to the liquid state. You have to completely melt every crystal or the liquid will quickly re-solidify. You can repeat this cycle thousands of times, just as you can freeze and melt water as many times as you like.

If you want more info I would suggest Googleing on
"sodium acetate freezing" etc
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jester2005
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Joined: 12 Dec 2005
Posts: 47

PostPosted: Tue Dec 27, 2005 10:29 am    Post subject: Reply with quote

These are now on SALE at Inshops (Poundstretcher) for 2.50 a pair. I got a couple yesterday.
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Wildlifewriter
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Joined: 04 Aug 2005
Posts: 948
Location: Norn Iron

PostPosted: Tue Dec 27, 2005 12:09 pm    Post subject: Reply with quote

jester2005 wrote:
These are now on SALE at Inshops (Poundstretcher) for 2.50 a pair. I got a couple yesterday.

Thanks - that's good to know because I'll be needing new ones, now. Wuthered's warning above was well said - but just not quite timely enough. It's a dreadful story... Sad

Got in yesterday evening and spotted the handwarmer things. There's those things, I thought, I'll just re-charge them now, because I'll be doing some cache maintenance tomorrow and they might come in useful.

For Wildlifewriter, to think is to act. Pan of water on stove, handwarmer things in pan, gas on... Doorbell rings.



It's Jim from next door, wanting to borrow a corkscrew because he's broken his, in the middle of a dinner party.

Implement handed over. Pan boiling merrily. Phone rings in study.

It's a cousin from Scotland, with compliments of the season and a request for the work address of another, even more distant cousin. Fire up PC and read out info... Nerve-shattering shriek as smoke alarm goes off.

The alarms in my flat are not weedy little warbling things with PP3 batteries in - they're integrated, mains-driven, 110dBA sirens, which sound like Gabriel tuning up for the Day of Judgement. Clearly, something is not right.

The whole kitchen end of my flat is filled with white, choking chemical smoke, within which a saucepan glows cherry-red on the gas ring. I blast the whole area with a fire extinguisher, turn off the gas, move the pan - and answer the front door again.

It's Jim from next door and was I aware that my smoke alarm had gone off? While the air clears, I join Jim's party for a stiff brandy. Mrs Jim advises that leaving pans unattended on stoves is very foolish and dangerous, and did I not know this? Smile sweetly at Mrs Jim, with gritted teeth.

Outside, I have an interesting conversation with the Fire Brigade who have been called out by staff at the nearby nursing home. They are very good about it, and full of useful information about boiling pans, most accidents happen in the home, endless vigilance required, etc, etc.

Back to the party and Jim's teenage offspring have been joined by off-duty staff from the nursing home; they're playing Robbie Williams and drinking Tequila Slammers in the garage. After another hour of this I return to my flat, accompanied by one of the junior nurses who is going to "check that everything is all right."

Lesley (for this is her name) pronounces that - in her expert opinion - the air is fit to breathe, and starts drinking my Harvey's Bristol Cream straight from the bottle. She shows no inclination to leave.

It's one in the morning, and I'm rather tired and emotional. Mrs Jim looks in to see how things are going. Lesley tells her, in a loud whisper, that she "finds older men shtrangely 'tractive..." and starts singing The Fields of Athenry. With her worst suspicions about Wildlifewriter confirmed, Mrs Jim leaves, taking Lesley with her by the ear.

It's been a long day.





-Wlw.
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HighlandNick
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Joined: 30 Aug 2005
Posts: 635
Location: Highlands, Scotland

PostPosted: Wed Dec 28, 2005 10:03 am    Post subject: Reply with quote

Wildlifewriter wrote:

Mrs Jim leaves, taking Lesley with her


And I thought fairy tales were supposed to have a happy ending Very Happy Very Happy Very Happy
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jester2005
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Joined: 12 Dec 2005
Posts: 47

PostPosted: Wed Dec 28, 2005 9:30 pm    Post subject: Reply with quote

Now on sale in ALDI, 1.25 a pair!
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