[AR] Re: Fw: Hydrogen / oxygen news
- From: Henry Spencer <henry@xxxxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 30 Oct 2013 19:46:04 -0400 (EDT)
On Wed, 30 Oct 2013, Christopher Buchanan Shay wrote:
> For those who didn't see this, possible AR applications beyond fabrication?
> http://www.safeflameproject.eu
Pretty much nil. The key question to ask is, just how much electricity
does it need? With no gas storage, production has to keep up with use...
and electrolysis is terribly energy-intensive. (There is a reason why
industrial/fuel hydrogen *isn't* routinely made by electrolysis.) There's
a lot of power in even a modest flame, and that energy has to come from
somewhere.
For the sort of flame we're most interested in :-), the power is huge. A
useful rule of thumb is that for many types of rocket engine, power input
is roughly exhaust velocity (m/s) times thrust (N). (The jet power is
half that, but there are enough inefficiencies to typically require
something vaguely like a factor of two on the energy input...) A mere
thousand pounds of thrust (call it 5kN) at 250s Isp (call it 2.5km/s) is
circa a 12 *megawatt* flame. Megawatts of electricity involve serious
hardware -- think bus bars, not mere cables. (At the upper extreme, big
rocket engines typically are multi-gigawatt machines.) Not practical.
The one borderline exception is spacecraft maneuvering propulsion, where
there has long been interest in systems that slowly electrolyze water and
store the resulting gases to be burned (much more rapidly) in a GOX/GH2
thruster. This offers a dense non-hazardous main tank and fairly high
Isp, at the cost of relatively heavy and complex hardware and a constraint
that burns be small and widely spaced. (And also, tricky development --
several past attempts at such systems ended in nasty explosions, in one
case fatal to an experimenter. Although Tethers Unlimited recently
successfully hot-fired such a system.)
Henry Spencer
henry@xxxxxxxxxxxxxxx
(hspencer@xxxxxxxxxxxxx)
(regexpguy@xxxxxxxxx)
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