[Lancer409]

http://www.eddiebauer.com/eb/product..._id=27285&nv=5|21474|216&lview=&color=*&cm_cg=C216&tid=&c=&sc=&l p=v1i017

i've bought a lot of those little disposeable ones .. this one interests me because it's not something you throw away .. less trash ... how does it work though?


the disposeable ones last 8 or more hours .. and then you toss it ... this one lasts for only 30 minutes .. but it's re useable... how do you recharge it? after 30 minutes, how long do you have to wait before you can use it again? etc...

the website doesnt say jack .. anyone know?

Product Details
PVC pouch with food-grade sodium acetate and metal disc
Provide instant heat
Can be used over and over
Heat for up to 30 minutes
Safe and nontoxic
Imported
2¼"Lx4¼"Wx¼"H

[alligator]

I have one and they work very well. Mine is made by EZ Heat. If you want a detailed explanation, here you go. They are acetate packs that are reheated by boiling the pack.

An Acetate pack is a plastic pouch filled with sodium acetate
trihydrate, Na(C2H3O2)-3H2O. This is a crystalline solid that
melts at 58 C. The melt has the property of sustaining
considerable subcooling: the melt can be cooled to room temp-
perature and below, without crystallization occurring. However if
crystallization is initiated (in the practical unit, by bending
a metal disc included in the pouch), crystallization proceeds
with the release of the heat of fusion, at least until the
temperature increases to 58 C. The Acetate pack is reusable, by
remelting the contents in boiling water or a microwave oven. It
is reported, however, that spontaneous initiation
of crystallization occurs if the pack is lowered sufficiently in
temperature.

How much heat is available from an Acetate pack depends upon
the initial and final temperatures between which the pack is
used, and the thermal properties of sodium acetate trihydrate.
The device must heat itself from its initial temperature, so the
lower that is, the less useful heat is available. Also, there is
a final temperature below which no significant heat is provided
to a patient. Both of these temperatures depend upon the
conditions of use and the state of the patient, and therefore no
fixed "available heat" can be stated. However the available heat
can be estimated for several values of initial and final
temperatures, which provides at least comparisons with the
Iron pack.

The heat of fusion of sodium acetate trihydrate was estimated
from heats of formation for sodium acetate (solid) and sodium
acetate (3H20), from NBS Circ. 500 (USGPO, Wash. D.C., 1952),
and that for water from NBS Tech. Note 270-3 (USGPO, Wash. D.C.,
1968). The heat capacities of the solid and molten salts were
estimated by use of Kopp's Rule, modified by estimating the
contribution of water of crystallization as Cp = 9 cal/gmolK, and
water in the melt as Cp = 19 cal/gmoleK. The resulting heat
capacities are Cp = 51.7 cal/gmolK (0.38 cal/gramK) for the
solid, and Cp = 92.5 cal/gmolK (0.68 cal/gramK) for the melt.
(The utility of sodium acetate trihydrate in this application
comes from its heat of fusion, and not from an unusually
high heat capacity.)

If an Acetate Pack initially at temperature Ti is
"triggered", the release of heat of fusion will raise the
temperature until it reaches the melting point, 58C. Further
crystallization will only occur if heat is removed by transfer to
the surroundings. Based upon the thermochemical properties given
above, the following Table shows the fraction of the acetate that
will still be molten at 58 C, starting at the given Ti,
assuming that the phase transition is done adiabatically:

Ti Fraction still molten

10 C 0.49
20 C 0.60
30 C 0.70

Thereafter, as heat is removed, the pack will stay at 58 C
until the contents are totally frozen, and then the pack
temperature will fall. At how low a temperature is the heat from
the pack still useful? This will depend upon the cirumstances,
and therefore the total heat available from an Acetate pack was
calculated assuming different initial and final temperatures. In
the following table, this heat is given as calories/gram sodium
acetate trihydrate:

Final Temperature, Tf

Ti 10C 20C 30C

10 C 49.5 45.6 41.8
20 C 56.2 52.5 48.6
30 C 63.0 59.2 55.4

For comparison, just plain water, provided at 30 C, and used
until it reaches 10 C (probably not physiologically useful,
however), would provide 20 calories/gram. In fact, a hot water
bottle provided at 100 C (if it could be sufficiently insulated
during transport, say in a Thermos (TM) bottle) would provide 70
calories/gram, cooling from 100 C to 30 C, and therefore
outperform an Acetate pack. The advantage of the Acetate pack, of
course, is that it will retain its thermal potential for a long
time if not triggered, and is therefore an immediately available
source of low-level heat.

[MilkmanDan]

Could you now explain how glow sticks work.

[Scifience]

Originally posted by MilkmanDan:
Could you now explain how glow sticks work.

Start a new thread.

[wdlove]

In some cases thirty minutes wouldn't be long enough. I appreciate the fact that it's reusable.

[Apple Pro Underwear]

thanks for the link

i think i may get one set! i hate the cold!

[Xeo]

My dad has one of those. It's just a pouch. As alligator said, you boil it to "recharge" it, and then when you want to use it, you just snap a metal disc inside which starts the reaction. It's really cool to watch since it's in clear plastic. The liquid starts out clear as well, but when you pop the disc, whiteness comes from the metal and takes over the whole of the inside, and it becomes solid. It's really hot too.

I used to play with it all the time when I was a kid. I wonder if he still has it.

[alligator]

Here's how a glow stick works:

There are three components of a glow stick. There need to be two chemicals that interact to release energy and also a fluorescent dye to accept this energy and convert it into light. Although there is more than one recipe for a glow stick, a common commercial glow stick uses a solution of hydrogen peroxide that is kept separate from a solution of a phenyl oxalate ester together with a fluorescent dye. The color of the fluorescent dye is what determines the resulting color of the glow stick when the chemical solutions are mixed. The basic premise of the reaction is that the reaction between the two chemicals releases enough energy to excite the electrons in the fluorescent dye. This causes the electrons to jump to a higher energy level and then fall back down and release light.

Specifically, the chemical reaction works like this: The hydrogen peroxide oxidizes the phenyl oxalate ester, to form phenol and an unstable peroxyacid ester. The unstable peroxyacid ester decomposes, resulting in phenol and a cyclic peroxy compound. The cyclic peroxy compound decomposes to carbon dioxide. This decomposition reaction releases the energy that excites the dye.

[Scifience]

Originally posted by alligator:
Here's how a glow stick works:

There are three components of a glow stick. There need to be two chemicals that interact to release energy and also a fluorescent dye to accept this energy and convert it into light. Although there is more than one recipe for a glow stick, a common commercial glow stick uses a solution of hydrogen peroxide that is kept separate from a solution of a phenyl oxalate ester together with a fluorescent dye. The color of the fluorescent dye is what determines the resulting color of the glow stick when the chemical solutions are mixed. The basic premise of the reaction is that the reaction between the two chemicals releases enough energy to excite the electrons in the fluorescent dye. This causes the electrons to jump to a higher energy level and then fall back down and release light.

Specifically, the chemical reaction works like this: The hydrogen peroxide oxidizes the phenyl oxalate ester, to form phenol and an unstable peroxyacid ester. The unstable peroxyacid ester decomposes, resulting in phenol and a cyclic peroxy compound. The cyclic peroxy compound decomposes to carbon dioxide. This decomposition reaction releases the energy that excites the dye.

Ah, thanks for clearing that up. I prefer leaving it at "snap the thing and it turns on." At least someone who isn't a chemistry major can understand thaat.

[enaid]

Originally Posted by alligator

I have one and they work very well. Mine is made by EZ Heat. If you want a detailed explanation, here you go. They are acetate packs that are reheated by boiling the pack.

An Acetate pack is a plastic pouch filled with sodium acetate
trihydrate, Na(C2H3O2)-3H2O. This is a crystalline solid that
melts at 58 C. The melt has the property of sustaining
considerable subcooling: the melt can be cooled to room temp-
perature and below, without crystallization occurring. However if
crystallization is initiated (in the practical unit, by bending
a metal disc included in the pouch), crystallization proceeds
with the release of the heat of fusion, at least until the
temperature increases to 58 C.

Just out of curiosity, what exactly does bending the metal disc included, how does that start the crystallization process?

By the way, do you know when they were invented? I have seen them this year (2005) for the first time.

A curious gadget indeed.

Thanks

Enaid

[alligator]

I've seen them from at least 1980's. They have been around a while. You can recharge them immediately and any sudden jolt will set them off, not just the flexing of the disc.

[phantomdragonz]

wow, what an old thread to be brought back from the dead by a member with only one post...


I bet you found it by google?



I recently saw these at a snomobile expo... I remembered this thread... I did not have time to play with them and wait in the huge line to do so...


Zach

[enaid]

Originally Posted by phantomdragonz

wow, what an old thread to be brought back from the dead by a member with only one post...


I bet you found it by google?



I recently saw these at a snomobile expo... I remembered this thread... I did not have time to play with them and wait in the huge line to do so...


Zach

Yes, Google, it was. What surprised me was that the address pointed to Mac News Network, which I had read before.

Enaid

[enaid]

(...)

Sorry, not used to witing in this forum -that was a mere resend. Enaid

[enaid]

Originally Posted by alligator

I've seen them from at least 1980's. They have been around a while. You can recharge them immediately and any sudden jolt will set them off, not just the flexing of the disc.

Thank you, what a fast reply for such an old thread.

By jolt you mean the trigger is something electrostaic?or is it the shake that sets it off.

Last week we had a cold snap in Europe, I wonder whether other people is Reading this clutching a handwormer in front of the computer .

Thanks again, Enaid

[Dork.]

Originally Posted by enaid

Last week we had a cold snap in Europe, I wonder whether other people is Reading this clutching a handwormer in front of the computer .

This is a Mac forum, we're all being kept warm by the intense heat from our Powerbooks....