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Post by ash19256 on May 16, 2017 8:53:42 GMT
I've stated this before, but our rocketships have a NTR burn time measured in minutes, sometimes under 5 minutes. Coking builds up, send in cleaning robot, need deceleration burn, remove cleaning robot. Plus, our rocket nozzles will likely be plated in Amorphous Carbon (thermal conductivity, melting resistance)... So carbon buildup wouldn't even be a big issue, imho. The way I understand it is that coking affects the reactor core's uranium rods by changing their thermal conductivity. This means that the hot uranium is not being cooled effectively by the propellant flow, and this causes a meltdown. Soot deposits on the nozzle is of minor consequence. And considering that it's entirely plausible that the graphene coated fuel rods that are standard to my NTR designs are always running much hotter than the melting point of just about anything that could be deposited on the fuel rods, that's much less of a problem for my reactors I suspect.
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Post by RiftandRend on May 16, 2017 9:24:27 GMT
I've stated this before, but our rocketships have a NTR burn time measured in minutes, sometimes under 5 minutes. Coking builds up, send in cleaning robot, need deceleration burn, remove cleaning robot. Plus, our rocket nozzles will likely be plated in Amorphous Carbon (thermal conductivity, melting resistance)... So carbon buildup wouldn't even be a big issue, imho. The way I understand it is that coking affects the reactor core's uranium rods by changing their thermal conductivity. This means that the hot uranium is not being cooled effectively by the propellant flow, and this causes a meltdown. Soot deposits on the nozzle is of minor consequence. Using modded materials NTR cores can reach 4400K, easily hot enough to melt soot deposits.
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Post by zuthal on May 16, 2017 9:37:31 GMT
Not sure about that, actually - the sublimation point of carbon goes up quite a bit with increased pressure, until its triple point at ~4600 K and ~11 MPa - and given that chamber pressures in our NTRs are often quite a bit higher than that, over 100 MPa, I'd assume that even with 4400K graphene cheese NTRs, you still wouldn't be able to melt or sublimate the carbon.
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Post by nerd1000 on May 16, 2017 12:16:59 GMT
Here's an idea. After your engine burn, don't let the reactor cool down. Instead just throttle it to maintain operating temperature- this won't use much of your uranium, because the reactor has no radiators or coolant flowing through it. With the inside of the reactor at vacuum, the soot deposits will start to sublimate away. In case any larger bits flake off, before the next burn just flush the reactor core out with a shot of inert gas. I call this the 'self cleaning oven' approach to NTR decoking.
Patent pending, all rights reserved.
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Post by newageofpower on May 16, 2017 13:15:43 GMT
Not sure about that, actually - the sublimation point of carbon goes up quite a bit with increased pressure, until its triple point at ~4600 K and ~11 MPa - and given that chamber pressures in our NTRs are often quite a bit higher than that, over 100 MPa, I'd assume that even with 4400K graphene cheese NTRs, you still wouldn't be able to melt or sublimate the carbon. Graphene cheese is 4900k. I dunno, it should be possible to design your rocket around having a thin layer of graphite dust encrusted on the fuel rods? Or just fire im short bursts and liberally use cleaning robot. I'm not a fan of adding chemical solvents; beyond the performance hits, both TaHfC and Graphene are carbon- bearing materials that would fail catastrophically should sufficient carbon be stripped...
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Post by n2maniac on May 18, 2017 7:55:29 GMT
Here's an idea. After your engine burn, don't let the reactor cool down. Instead just throttle it to maintain operating temperature- this won't use much of your uranium, because the reactor has no radiators or coolant flowing through it. With the inside of the reactor at vacuum, the soot deposits will start to sublimate away. In case any larger bits flake off, before the next burn just flush the reactor core out with a shot of inert gas. I call this the 'self cleaning oven' approach to NTR decoking. Patent pending, all rights reserved. Legitimate question: does carbon sublimate faster than the nuclear fuel / nuclear fuel cladding?
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Post by RiftandRend on May 18, 2017 8:06:20 GMT
Here's an idea. After your engine burn, don't let the reactor cool down. Instead just throttle it to maintain operating temperature- this won't use much of your uranium, because the reactor has no radiators or coolant flowing through it. With the inside of the reactor at vacuum, the soot deposits will start to sublimate away. In case any larger bits flake off, before the next burn just flush the reactor core out with a shot of inert gas. I call this the 'self cleaning oven' approach to NTR decoking. Patent pending, all rights reserved. Legitimate question: does carbon sublimate faster than the nuclear fuel / nuclear fuel cladding? This sort of system would only be possible for reactors with encapsulated fuel such as TaHfC with a melting point of 4400K. If you properly control temperature only the carbon should melt.
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Post by n2maniac on May 18, 2017 8:23:09 GMT
Legitimate question: does carbon sublimate faster than the nuclear fuel / nuclear fuel cladding? This sort of system would only be possible for reactors with encapsulated fuel such as TaHfC with a melting point of 4400K. If you properly control temperature only the carbon should melt. Vapor pressure and sublimation rate are at stake for feasibility. Melting point is a prerequisite.
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