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Can we use advanced thermoelectric materials to reduce the temperature of nozzles by converting heat energy to electric energy and reducing the strain on the nozzle material and the coolant while storing some electricity?

If no, is there any way to convert this heat into other usable forms (s) to reduce the workload of the coolant?

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    $\begingroup$ What would you use the electricity for? Rockets don't need much in the way of electrical power. $\endgroup$
    – GdD
    May 10, 2021 at 10:49
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    $\begingroup$ Unless it's electric-pump-fed engine. $\endgroup$
    – Bojan Kogoj
    May 10, 2021 at 11:22

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This would not be useful in general. Thermoelectric converters don't convert heat into electrical power, they generate electrical power from the flow of heat across them. You still need to cool the cold side, or the thermoelectric junctions will just burn up. The low efficiency of thermoelectric conversion means you're only removing a small fraction of the heat to be dissipated in the electrical circuit.

Worse, the thermal resistance of the thermoelectric converter is lowest if it is short circuited, any attempt to use the electricity will interfere with cooling...not a good idea when it comes to rocket nozzles. It would actually make more sense to drive electrical power through the junctions to operate them as a thermoelectric cooler, but the power requirements would be unworkable. Additional problems are the mass of all the thermoelectric material required and the failure modes if the circuit is broken...efficient thermoelectric materials are specifically chosen to have high thermal resistance on their own.

You could perhaps use thermoelectric generation to run some small sensors, but sensors that won't operate until the engine warms up aren't very desirable.

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  • $\begingroup$ Do you know some rough numbers for how much power you could squeeze out of these? Assume you have an electric pump rocket engine so you can sink as much current into it as you need (effectively shorting the thermoelectric system). Also assume you could put this near the maximum temperature it can withstand, so not touching the combustion chamber, but far enough to be in spec, and cooled by liquid methane/oxygen so about 100K on the cold side. Could you get enough power to drive the pumps? and how much extra weight would it add. $\endgroup$
    – csiz
    May 10, 2021 at 23:02
  • $\begingroup$ > Could you get enough power to drive the pumps? Almost certainly not, unfortunately. Thermoelectric systems are great in all sorts of ways, but tend to have terrible efficiency. (Roughly speaking: they demand materials with high electrical conductivity but low thermal conductivity, but high electrical conductivity tends to imply high thermal conductivity...) That being said, as a rugged source of auxiliary power...? Maybe. $\endgroup$
    – TLW
    May 10, 2021 at 23:28
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    $\begingroup$ @csiz The only thing to calculate is how many orders of magnitude you fall short by. As a general idea, you need around 10 megawatts of pumping power for something with fairly modest chamber pressures like the Merlin 1D. A GPHS-RTG minus the plutonium pellet masses about 50 kg for 300 W...taking that as representative of a complete system with radiators and such, that's 2000 tons of thermoelectric generators to run the Falcon 9 upper stage's pump. The complete Falcon 9 stack only masses around 550 tons, propellant and all. $\endgroup$
    – Christopher James Huff
    May 10, 2021 at 23:49
  • $\begingroup$ @TLW An RTG is rugged because it's simple heat pipes and thermoelectric junctions wrapped around a quiet, compact little radiothermal source that stays at a constant high temperature. A rocket nozzle is a bit livelier, and I wouldn't run anything critical from TEGs mounted on one. $\endgroup$
    – Christopher James Huff
    May 10, 2021 at 23:54
  • $\begingroup$ @ChristopherJamesHuff - I think we're talking about two rather different scales here. Mounting thermoelectrics in an F-1 is somewhat livelier than, say, a TR-201. $\endgroup$
    – TLW
    May 11, 2021 at 0:07

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