> >Maybe you could use water cooling on a test stand and dump cooling for a
> >test flight?
> Water cooling for a small motor ( < 100 lbf or so ) can be done by just
> hooking a garden hose up to a double walled chamber. Even easier, just
> letting water fall on a heat sink chamber can greatly extend the available
> run time (at the expense of making a lot of steam that obscures things a
bit).
BOTE calc suggests that taking water from ambient to steam * with a bit of
heating beyond that takes about 1 kWh/kg. Typical propellants will run in
the 5 to 15 kWh / kg total available energy range **. Depending on how much
energy you "leave behind" this suggests water cooling requires equal or
greater mass of water to propellant. If you have a hose then 10 times sounds
a good idea :-).
Lets see. 100 lbf at Isp = 150 = 2/3lbf/second propellant = about 0.1 US
gallons/second. Hose sounds good.
E&OE
Russell McMahon
* Water latent heat of vaporisation = 2.26 MJ/kg = 627 watt-hour/kg.
Add a bit for heating water to bp and heat the steam a bit as well and you
may push 1 kWh/kg.
** Except if you are using Hydrogen which is about 3 times higher than
anything else.
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