mrericboyd at yahoo.com
Wed Mar 17 19:02:05 UTC 2010
Have you considered simply including a bottle of hot water in the
payload? I bet it would prevent the payload from going below freezing:
the latent heat of fusion is quite large, equivalent to cooling water
about 80 degrees (with zero temperature change). Plus you get to cool
the hot water itself.
Of course, you might want to run a vacuum test on whatever container you
choose just to be sure it won't burst :-)
On 3/17/10 11:48 AM, Christie Dudley wrote:
> (Psst. 'reply all' works wonders.)
> Thanks Ben for your research. The target we're after is to keep it warm
> for 5 hours. If the hand warmer only heats to 100F, I think we're also
> concerned that it'd be hot enough to keep our stuff warm. The G1 was
> measuring -20 on it's internal measure which is heated by battery and
> the APRS packet we got through was colder than that.
> "We also briefly discussed having officers replaced by very small shell
> scripts." -- Noisebridge meeting notes 2008-06-17
> The outer bounds is only the beginning.
> On Tue, Mar 16, 2010 at 10:49 PM, Ben Rupert <meowdip at gmail.com
> <mailto:meowdip at gmail.com>> wrote:
> Hey, sorry I didn't respond earlier. After talking to Christie on
> Sunday about the heating problems i understand your needs and
> constraints better and have done some research and calculations. I had
> thought about trying to find oxygen in a cartridge similar to the little
> CO2 cartridges used for some BB guns. I couldn't find any that would
> hold enough oxygen in a single unit for a single hand warmer. In fact
> the only ones I could find would take around 5-6. I also considered
> suggesting using a 30% hydrogen peroxide solution instead of compressed
> oxygen (grocery store stuff is 3%). This won't work either as you would
> need about 500g of this solution to burn a single hand warmer. Although
> on the plus side I think I came up with a cleaver and lightweight method
> to introduce the solution at a controlled rate. You could use
> concentrated nitric acid, but you really shouldn't. If it leaked it
> would destroy pretty much anything it came in contact with and might
> also burn through whatever you used to contain the hand warmer.
> The other question though, how long is your flight expected to last?
> Those hand warmers get to just above 100 F, and stay there for up to
> eight hours. If you don't expect to need to heat for that long maybe
> you can just have less oxidant around and let the container collapse at
> the end.
> I'll search some databases at work tomorrow for other reactions which
> might work better as well.
> Christie Dudley wrote:
> > Well, if we're trying to avoid condensation, then we'd actually
> want to
> > keep stuff above the dew point. Not sure what that would be at that
> > level, and it probably varies depending on clouds, etc.
> > The camera lens would probably be the biggest consumer of heat. It
> > generates no heat itself, has limited insulation opportunity and has
> > significant degradation from cold. Although it doesn't
> completely stop
> > working, the current theory is that the camera itself stopped because
> > off condensation.
> > I like the idea of a controlled chemical reaction. We'd
> discussed hand
> > warmers already, but dismissed those because of the need for oxygen,
> > which is obviously limited in that thin atmosphere. I've cc'd Ben
> > Rupert, a recent NB convert who knows quite a lot about chemistry
> to see
> > if he might be able to help with this discussion.
> > Christie
> > _______
> > "The road of excess leads to the palace of wisdom." -- W. Blake.
> > The outer bounds is only the beginning.
> > http://www.flickr.com/photos/genriel/sets/72157623376093724/
> > On Fri, Feb 12, 2010 at 9:10 AM, Christoph Maier
> > <cm.hardware.software.elsewhere at gmail.com
> <mailto:cm.hardware.software.elsewhere at gmail.com>
> > <mailto:cm.hardware.software.elsewhere at gmail.com
> <mailto:cm.hardware.software.elsewhere at gmail.com>>> wrote:
> > On Thu, 2010-02-11 at 23:48 -0800, Joachim Pedersen wrote:
> > > So, 555timers are really small ICs, which can't really push
> that much
> > > current, so you would need to have the 555 trigger some kind of
> > > FET methinks. Also, resistive heating is notoriously inefficient...
> > It is, because you lose a lot of heat in the controller, in
> > if you don't use PWM.
> > However ... we want to heat some stuff up to the point where
> > are cozy and warm, not higher.
> > The most efficient way to do this is to use the regulating
> > _themselves_ as heating elements - mounted together with the
> devices we
> > want to heat on a good thermal conductor (i.e., a block of
> > and wrap a good thermal shield (that also serves as padding
> to prevent a
> > reasonably solid piece of metal hitting something at landing)
> around it.
> > The electronics would contain power transistors as heating
> elements, an
> > adjustable temperature regulator, e.g.,
> > LM56 or LM57 [ http://www.national.com/cat/index.cgi?i=i//73 ,
> > http://www.national.com/cat/index.cgi?i=i//71 ]
> > and a few resistors and capacitors.
> > Christoph
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