chemical heat

Has anyone tried putting those chemical heat packs inside their drysuit for
warmth? It's a little cold at the moment...

"stuie" <srobins@pobox.panties.com> wrote in message
news:WjcWb.1937$h44.374181@stones.force9.net...
> Has anyone tried putting those chemical heat packs inside their drysuit
for
> warmth? It's a little cold at the moment...
If I remember correctly they work by the rapid oxidation of iron , usually
using air as a catalyst.
I wouldn't like to say what exactly would happen if you got sea-water in
them, and I'm not totally sure that an increase in pressure might not cause
an increase in the rate of the reaction and make them silly-ly hot.

Unless somebody can actually find out exactly what reaction they're using
and does the chemistry I'd avoid it.

Alun Harford

"Alun Harford" <alunharford@yahoo.com> wrote in message
news:c0bkql$ile$1@pegasus.csx.cam.ac.uk...
> "stuie" <srobins@pobox.panties.com> wrote in message
> news:WjcWb.1937$h44.374181@stones.force9.net...
> > Has anyone tried putting those chemical heat packs inside their drysuit
> for
> > warmth? It's a little cold at the moment...
> If I remember correctly they work by the rapid oxidation of iron , usually
> using air as a catalyst.
> I wouldn't like to say what exactly would happen if you got sea-water in
> them, and I'm not totally sure that an increase in pressure might not
cause
> an increase in the rate of the reaction and make them silly-ly hot.

I suspect Stuie is referring to the packs of gel that rely on the latent
heat of crystallisation in turning from a liquid to a solid. The
solidification is exothermic and is initiated by rubbing a pin inside the
bag to seed the crystallisation. The packs can later be "recharged" by
boiling them for about 20 minutes.

They do tend to get rather warm and once sealed inside a drysuit there is no
chance of taking them out or moving them to another point. A nice dilemma -
freeze or burn?

Cliff.

"Alasdair Allan" <aa@ukrecscuba.org.uk> wrote in message
news:c0bmlc$15ljim$1@ID-188041.news.uni-berlin.de...
> Alun Harford wrote:
> > I wouldn't like to say what exactly would happen if you got sea-water in
> > them, and I'm not totally sure that an increase in pressure might not
cause
> > an increase in the rate of the reaction and make them silly-ly hot.
>
> My chemsitry is very (very) rusty, and most of the stuff I do know takes
> place at temperatures and pressures that you don't find until you're in
> standoff accretion shocks near a white dwarf or neutron star surface (lets
> just say thats rather hot, and that a chemist wouldn't really call it
> chemistry anymore, and leave it at that), but I'd also be worried about
> what the pressure increase might do to the reaction.
>
> I'd be very tempted to say that the increase in presure would almost
> certainly speed the reaction, which could mean you get very hot indeed.
>
> > Unless somebody can actually find out exactly what reaction they're
using
> > and does the chemistry I'd avoid it.
>
> Ditto. Any chemists on the group? I vaguely remember we had one or two
> hanging around.

I'm currently doing Chemistry at Cambridge - but it's not like I know what
I'm talking about (first year).
And you're right - chemistry is a practical subject so the stuff that's
impossible to do at the moment, is done by people who write down pointless
(usually wrong) stuff on the back of an envelope. PHYSICISTS.

I'm tempted to say that an increase in pressure is unlikely to significantly
change the reaction rate (it's not a gas), but I wouldn't risk a fire inside
my drysuit in order to try it.
It might push the equilibrium further over to the products though, which
would increase the rate - but I can't tell you that unless I knew what
exactly was in those things and how they work.

Alun Harford

Alun Harford wrote:
> It might push the equilibrium further over to the products though, which
> would increase the rate...

That was my thought...

> ...but I can't tell you that unless I knew what exactly was in those
> things and how they work.

....and ditto.

Al.

"Alun Harford" <alunharford@yahoo.com> wrote in message
news:c0bngu$kmr$1@pegasus.csx.cam.ac.uk...
> "Alasdair Allan" <aa@ukrecscuba.org.uk> wrote in message
> news:c0bmlc$15ljim$1@ID-188041.news.uni-berlin.de...
> > Alun Harford wrote:
> > > I wouldn't like to say what exactly would happen if you got sea-water
in
> > > them, and I'm not totally sure that an increase in pressure might not
> cause
> > > an increase in the rate of the reaction and make them silly-ly hot.
> >
> > My chemsitry is very (very) rusty, and most of the stuff I do know takes
> > place at temperatures and pressures that you don't find until you're in
> > standoff accretion shocks near a white dwarf or neutron star surface
(lets
> > just say thats rather hot, and that a chemist wouldn't really call it
> > chemistry anymore, and leave it at that), but I'd also be worried about
> > what the pressure increase might do to the reaction.
> >
> > I'd be very tempted to say that the increase in presure would almost
> > certainly speed the reaction, which could mean you get very hot indeed.
> >
> > > Unless somebody can actually find out exactly what reaction they're
> using
> > > and does the chemistry I'd avoid it.
> >
> > Ditto. Any chemists on the group? I vaguely remember we had one or two
> > hanging around.
>
> I'm currently doing Chemistry at Cambridge - but it's not like I know what
> I'm talking about (first year).
> And you're right - chemistry is a practical subject so the stuff that's
> impossible to do at the moment, is done by people who write down pointless
> (usually wrong) stuff on the back of an envelope. PHYSICISTS.
>
> I'm tempted to say that an increase in pressure is unlikely to
significantly
> change the reaction rate (it's not a gas), but I wouldn't risk a fire
inside
> my drysuit in order to try it.

Stick one in a ziplock clear bag with at thermometer taped to it and take it
down... If it melts the bag you know not to try.. if it's still hanging
together just read off the thermo... it may take several thermoeters to find
one that doesn't implode ")

rhys


> It might push the equilibrium further over to the products though, which
> would increase the rate - but I can't tell you that unless I knew what
> exactly was in those things and how they work.
>
> Alun Harford
>
>

"rnf2" <rnf2@NOSPAMwaikato.ac.nz> wrote in message
news:40297f4e$1@news.iconz.co.nz...
>
> "Alun Harford" <alunharford@yahoo.com> wrote in message
> news:c0bngu$kmr$1@pegasus.csx.cam.ac.uk...
> > "Alasdair Allan" <aa@ukrecscuba.org.uk> wrote in message
> > news:c0bmlc$15ljim$1@ID-188041.news.uni-berlin.de...
> > > Alun Harford wrote:
> > > > I wouldn't like to say what exactly would happen if you got
sea-water
> in
> > > > them, and I'm not totally sure that an increase in pressure might
not
> > cause
> > > > an increase in the rate of the reaction and make them silly-ly hot.
> > >
> > > My chemsitry is very (very) rusty, and most of the stuff I do know
takes
> > > place at temperatures and pressures that you don't find until you're
in
> > > standoff accretion shocks near a white dwarf or neutron star surface
> (lets
> > > just say thats rather hot, and that a chemist wouldn't really call it
> > > chemistry anymore, and leave it at that), but I'd also be worried
about
> > > what the pressure increase might do to the reaction.
> > >
> > > I'd be very tempted to say that the increase in presure would almost
> > > certainly speed the reaction, which could mean you get very hot
indeed.
> > >
> > > > Unless somebody can actually find out exactly what reaction they're
> > using
> > > > and does the chemistry I'd avoid it.
> > >
> > > Ditto. Any chemists on the group? I vaguely remember we had one or two
> > > hanging around.
> >
> > I'm currently doing Chemistry at Cambridge - but it's not like I know
what
> > I'm talking about (first year).
> > And you're right - chemistry is a practical subject so the stuff that's
> > impossible to do at the moment, is done by people who write down
pointless
> > (usually wrong) stuff on the back of an envelope. PHYSICISTS.
> >
> > I'm tempted to say that an increase in pressure is unlikely to
> significantly
> > change the reaction rate (it's not a gas), but I wouldn't risk a fire
> inside
> > my drysuit in order to try it.
>
> Stick one in a ziplock clear bag with at thermometer taped to it and take
it
> down... If it melts the bag you know not to try.. if it's still hanging
> together just read off the thermo... it may take several thermoeters to
find
> one that doesn't implode ")

Well if you're going to do it use a newish thermometer (ie. non-Hg).
Hmm... I suppose it depends if you like eating fish though.

Alun Harford

> I wouldn't risk a fire inside
> my drysuit in order to try it.

mmmm - toasty warm! :O)

David

Cliff Coggin wrote:
> I suspect Stuie is referring to the packs of gel that rely on the
> latent heat of crystallisation in turning from a liquid to a solid.
> The solidification is exothermic and is initiated by rubbing a pin
> inside the bag to seed the crystallisation. The packs can later be
> "recharged" by boiling them for about 20 minutes.

After Digs used one to thaw my turtle handsets when they iced up
I carry a couple now. I suspect that the reaction is over quite quickly
but the heat only leaches out slowly. If you watch the crystalisation
it runs throught the pouch quite fast. Mine have a clicker to fire them
off.

Saying that I'm a bit wary to try it incase I'm wrong. Any how I have
a suit that works so I'm not aware of needing assistance in that
department yet.

nigelH

I remember a kind soul handed me one of those when my dry suit flooded in
the Farne Islands.
Kept my hands warm for 5 mins but then far from impressive.