Re: New Igniter Project Update

Russell McMahon wrote:
> 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 **.

But only 2% or so makes it through the wall- don't forget you are 
cooling the metal *not* the combustion gas- [just as well since cooling 
the combustion gas has an unfortunate effect on the ISP :-) ]

> Depending on how much
> energy you "leave behind" this suggests water cooling requires equal or
> greater mass of water to propellant.

Much, much less than that.

You're mostly limited by heat transfer efficiency in the cooling ducts.

> 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.
> 
>         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.

Yes, and even more than that if you pressurize the water. Critical 
temperature is up past 350C. You can even recover some performance if 
you put the hot steam through a DeLaval nozzle. The ISP of steam is up 
to 190 seconds.