[ERPS] immersion cooled chamber

[John Carmack]

We are going to try something that I have seen Doug swear up and down won't work -- water immersion cooling.  I have a number of "nudges" that may add up to enough to make it viable:

Peroxide is cooler burning than most propellent mixtures.

We are only running at around 150 psi chamber pressure.

Adding a surfactant to the water may reduce the amount of gas film stuck to the walls.

Machine lots of vertical fins/channels into the outside of the chamber so you have about 3x the surface area of the chamber for dissipating heat into the water.

Construct the chamber out of thick aluminum, so it has good internal heat transfer to allow heat to flow into the fins and around localized hot spots, but hard anodize the interior as a thermal barrier to reduce heat transfer into the aluminum.

Add a baffle around the chamber that is open at the bottom, so the water does some amount of forced convective circulation:

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------|w|w|
      |w|w|\   /
      |w|w| \ /
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      -----/   \

Or, it might be better to take the internal baffle above the water level, so fresh water only comes in the bottom as the water inside the baffle is boiled off.

My thinking is that it would be an "externally ablative" engine.  Instead of pyrolizing a resin inside the chamber to draw the heat away, the heat soaks into the chamber like a heat sink engine, then boils water farther away.  Boiling water should be more mass efficient of a heat sink than typical ablative materials, so the only question is if the heat transfer can be kept up once the water starts flashing to steam.  If the walls are thick enough, it will heat sink around enough that temporary local areas that are steam covered shouldn't be a problem if the system average is high enough.

This will be a whole lot simpler to fabricate than a regenerative system, and avoids the trapped propellent issue and the uncooled nozzle at peroxide depletion issue.  I really wouldn't care all that much if the required water amounted to

We are probably going to bolt a quickie brass chamber to the bottom of a pail full of water and just see what happens, before making a more specialized aluminum chamber.  Anyone want to place bets on how many seconds it will take for the motor to burn through?

John Carmack