[kmlchicago]

My research group needs a mechanical trigger for an exothermic reaction which will heat a battery from -180C to -20C.  We have looked into using handwarmers, but they all use water and therefore won't function in a cold vacuum, which is required for the project.  I need a chemical reaction to heat a set of batteries that will still work at -180C and is easily trigger-able.  My research group is planning on putting the computer and batteries in a hermetically-sealed container, so if the reaction uses a specific gas that isn't too hard to obtain, we could potentially fill the container with it.  Anything involving combustion is out of the question, as this will be in close proximity to sensitive electronics.  We also don't have a huge mass or volume budget...  We're heating nine cells which are in a carbon-fiber casing.

Any ideas?

[strat]

It's just a thought, but what about sodium acetate heat packs? They're mechanically triggered and work through the heat of crystallization.

http://www.9thtee.com/reheater.htm

[macman104]

sodium acetate heat packs have water in them

Does it have to be a reaction that heats it?  I think finding a reaction that will take place at any appreciable rate at 180C, be controlled enough to stop at -20C, will be tough.  Is there a way to put a heating mantle in there, or some other electrically powered heating device?