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.
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