Feel the Heat (was Re: Nuclear heater for Expeditions)

Michael Butler (mmb@best.com)
Tue, 6 Jan 1998 16:35:43 -0800 (PST)

On Tue, 6 Jan 1998, Adam Foust wrote:
> How about a small chemical heater of some sort that cleanly and
> efficiently metabolizes some substance and generates heat as a
> byproduct? Like an ideal fuel cell? Humans maintain an average body
> temp of 98.6F from metabolizing a variety of molecules broken
> down from food substances; couldn't something much much simpler
> than a life form perform something similar for the specific purpose
> of generating varying levels of heat efficiently?

So far, you're spot on. There used to be little naphtha-fired catalytic
heaters the size of a thin bar of soap that you could buy at sporting
goods stores, for pocket handwarmers. I don't know if they're still sold,
or if not, why not; maybe one too many sauced ice fishermen with
frostbite damage compounded by third-degree burns?. Getting complete
combustion seems a bit tricky, but I see no reason why you couldn't put a
platinum post-stage combustor on one. Cost would go up, of course.

A microprocessor-mediated warmer of this type seems possible, as does
combustion regulation using bimetals or shape memory alloys.

> Is breaking down
> water from melting snow, slowly burning the H and exhausting the O2
> possible in a tiny device with today's tech? This would seem a
> practical level of tech for camping in cold environments with
> moisture in some form present.

Problem is, you've got it backwards. The H is already burned. That's what
oxidation _is_ (*doh!*). So you have to pump energy into the water to
electrolyze it, at least according to conventional models. Danny may think
differently. :)

> to manufacture personal heater devices "out there" unless they
> could sell them "here" or other places for use in uncontrolled
> temperature environments (like the surfaces of planets)?...

Personal heaters, water heaters and the like made by using relatively
"hot" radioisotopes are, in the narrowest technical sense, a terrifically
appropriate use of energy that would otherwise go to waste. The heat is
going to be generated whether those ceramic pellets are at the bottom of a
mineshaft or embedded in your self-heating floor. The environmentally
tricky part is picking isotopes with nuclear decay paths that don't result
in unmanageable neutron-activation of surrounding materials, or gamma
radiation, or radon emission. This could be a tall order; I'm no expert.

However, given how flipped-out people are about something as unthreatening
as asbestos-based building materials, which are mostly only dangerous
while you're creating them or (trying to) destroy them, I don't see
passive heat pellets (which share that threat profile) making any
commercial headway in the current culture.

> Technology-wise, Mr. Fusion is a great idea. ;)
> > I've heard that traditional Korean houses are heated by a
> > wood-burning stove under the house whose chimney is a meandering
> > ceramic pipe buried in the floor. A high-tech version of this might
> > let you put the burner outside the tent while still getting nearly
> > all the heat into the tent.

The Romans used to do this; they might have gotten the idea from the
Etruscans. Transfer efficiency can be high; cleaning the chimney can be
easy or a bitch, all depending on your design details.

> That's sounds like a good innovation that could be applied for
> today's camping gear. You might even invert this: have the (tiny)
> heater sit inside the tent, and have small, flexible, insolated
> pipes (hoses?) vent in air and out exhaust. Or would this be
> an unworkable contraption on the small-scale? Maybe an arctic
> survival heater similar to this already exists? Or would this be
> an unworkable contraption on the small-scale?

Having been doing a little study in the area of thermal transfer in the
shirtsleeve-to-burning-paper regime lately, permit me to take a BOE shot:

Seems to me what you want is a pair of heat exchangers, one to preheat the
incoming air, the other to draw heat from the exhaust and put it into
circulating ("house") air and the preheater. Duct them (both?) from
outside, get good circulation inside the tent, don't let the firebox leak,
and you're in there. If you only duct the exhaust, there are tradeoffs:
slightly simpler system, but possibly some drafts. No matter what,
there's also always going to be some chance that a poorly-set-up system or
changing winds could interfere with proper operation due to pressure
heads. Such interference could be, in worst case, fatal (fire, CO).

I am sure there is a weight and size penalty for those
heat exchangers. How much? Depends on your tech, I'd guess.

> [Adam Foust] * agfoust@farthest.com * http://farthest.com