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Post by Crazy Tom on Feb 2, 2017 18:54:36 GMT
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Post by bigbombr on Feb 2, 2017 21:51:59 GMT
Someone already suggested this. I don't think it has it's own suggestion thread though. Wouldn't the rapid heating and cooling cause a lot of thermal expansion stress or make the fuel brittle?
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Post by Crazy Tom on Feb 2, 2017 22:25:58 GMT
Someone already suggested this. I don't think it has it's own suggestion thread though. Wouldn't the rapid heating and cooling cause a lot of thermal expansion stress or make the fuel brittle? One assumes that the issue already has a solution, given the operation of the TRIGA reactors its based on. |
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Post by RiftandRend on Feb 6, 2017 19:12:42 GMT
Someone already suggested this. I don't think it has it's own suggestion thread though. Wouldn't the rapid heating and cooling cause a lot of thermal expansion stress or make the fuel brittle? I imagine that can be solved with some bracing or clever arrangement of the fuel rods. |
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Post by darthroach on Feb 7, 2017 0:12:15 GMT
So it's a NERVA that can go toe to toe with interplantery Orions. What's more, it could conceivably get approved by some bureaucrats somewhere? Astonishing. Hope they make this work. |
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Post by RiftandRend on Feb 7, 2017 19:36:05 GMT
Even better, its not some incredibly complex thing that would need decades of research to build. I could see this being added to the game relatively easily.
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Post by phoboshine on Feb 9, 2017 20:24:06 GMT
Even better, its not some incredibly complex thing that would need decades of research to build. I could see this being added to the game relatively easily. I like this pulsed solid NTR. But I have a doubt. If Isp is produced by a pulse, then the maximun Isp is not limited by radiative heat transfer, because the temperature at the pulse will be inmense and then will decay very fast. But in other rockets the propellant is heated continuously from cold to hot and then never will reach very high temperatures, say 20000 K. In other words the problem with the propellant in the pulsed solid NTR would be that it must be ejected from the rocket as soon as possible or will be cooled very fast. At 20000K or 30000 K radiative heat transfer is very strong |
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Post by darthroach on Feb 9, 2017 20:29:39 GMT
Even better, its not some incredibly complex thing that would need decades of research to build. I could see this being added to the game relatively easily. I like this pulsed solid NTR. But I have a doubt. If Isp is produced by a pulse, then the maximun Isp is not limited by radiative heat transfer, because the temperature at the pulse will be inmense and then will decay very fast. But in other rockets the propellant is heated continuously from cold to hot and then never will reach very high temperatures, say 20000 K. In other words the problem with the propellant in the pulsed solid NTR would be that it must be ejected from the rocket as soon as possible or will be cooled very fast. At 20000K or 30000 K radiative heat transfer is very strong Since this is all happening within a reaction chamber, and the pulses are spaced rather closely together, wouldn't radiative transfer and conduction simply result in a sort of dampening in average temperature? That would be the case if the propellant spends more than 1 period inside the engine. This would, of course, bring the average temperature down quite a bit. But "quite a bit" is a relative term and the Isp would still blow everything we currently have out of the water. I don't think anyone has fully done the, math, however. I wish I understood nuclear reactors well enough to make an attempt, but alas, I am hardly beyond an informed layman on the topic. |
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Post by vegemeister on Feb 10, 2017 19:19:59 GMT
Here's the paper: u.nya.is/lxewyl.pdfIt doesn't look very promising. From table 1, at least 93% of the energy is going into the fuel instead of the propellant (via the fission fragments, which don't, AFAIK, easily pass through solid matter). So to get the propellant hotter than the fuel, you have to get rid of that heat somehow. Up to the max service temperature of the fuel, you could use regenerative cooling. But that would only get the propellant a little hotter (about 7.5% hotter) than you could in a conventional NTR. To get a substantial improvement in Isp, you'd have to get rid of the fission fragment heat somewhere else, i.e., with radiators. You can still use some regenerative cooling, but the higher you want to push the Isp, the more of the heat going into the propellant has to come from neutron collisions. This could make a decent hybrid design, if you used the heat to generate power and run an MPD. Assuming you design such that the MPD and the pulsed NTR have the same ISP, it looks like half again as much thrust than the MPD alone. But we have magical near-Carnot efficiency thermoelectrics, so IRL it would probably be a lot more useful. The paper claims this could be used to increase thrust as well, by increasing the average power of the reactor and using greater mass flow, but I don't see why that's better than running the reactor at higher power in stationary mode. Either way you have to to get the heat out of the fuel and into the propellant. |
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Post by RiftandRend on Feb 11, 2017 23:31:34 GMT
Here's the paper: u.nya.is/lxewyl.pdfIt doesn't look very promising. From table 1, at least 93% of the energy is going into the fuel instead of the propellant (via the fission fragments, which don't, AFAIK, easily pass through solid matter). So to get the propellant hotter than the fuel, you have to get rid of that heat somehow. Up to the max service temperature of the fuel, you could use regenerative cooling. But that would only get the propellant a little hotter (about 7.5% hotter) than you could in a conventional NTR. To get a substantial improvement in Isp, you'd have to get rid of the fission fragment heat somewhere else, i.e., with radiators. You can still use some regenerative cooling, but the higher you want to push the Isp, the more of the heat going into the propellant has to come from neutron collisions. This could make a decent hybrid design, if you used the heat to generate power and run an MPD. Assuming you design such that the MPD and the pulsed NTR have the same ISP, it looks like half again as much thrust than the MPD alone. But we have magical near-Carnot efficiency thermoelectrics, so IRL it would probably be a lot more useful. The paper claims this could be used to increase thrust as well, by increasing the average power of the reactor and using greater mass flow, but I don't see why that's better than running the reactor at higher power in stationary mode. Either way you have to to get the heat out of the fuel and into the propellant. The documentation I have seen describes an active cooling system separate from the propellent flow. |
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Post by vegemeister on Feb 12, 2017 5:43:08 GMT
Here's the paper: u.nya.is/lxewyl.pdfIt doesn't look very promising. From table 1, at least 93% of the energy is going into the fuel instead of the propellant (via the fission fragments, which don't, AFAIK, easily pass through solid matter). So to get the propellant hotter than the fuel, you have to get rid of that heat somehow. Up to the max service temperature of the fuel, you could use regenerative cooling. But that would only get the propellant a little hotter (about 7.5% hotter) than you could in a conventional NTR. To get a substantial improvement in Isp, you'd have to get rid of the fission fragment heat somewhere else, i.e., with radiators. You can still use some regenerative cooling, but the higher you want to push the Isp, the more of the heat going into the propellant has to come from neutron collisions. This could make a decent hybrid design, if you used the heat to generate power and run an MPD. Assuming you design such that the MPD and the pulsed NTR have the same ISP, it looks like half again as much thrust than the MPD alone. But we have magical near-Carnot efficiency thermoelectrics, so IRL it would probably be a lot more useful. The paper claims this could be used to increase thrust as well, by increasing the average power of the reactor and using greater mass flow, but I don't see why that's better than running the reactor at higher power in stationary mode. Either way you have to to get the heat out of the fuel and into the propellant. The documentation I have seen describes an active cooling system separate from the propellent flow. I mentioned that. The active cooling system would have to deal with most of the power output of the nuclear reactor in order for there to be a substantial Isp benefit over traditional NTRs. That means big ol' radiators. But it would would synergize well as a hybrid engine using the electricity to power an MPD. |
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Post by RiftandRend on Feb 12, 2017 6:52:38 GMT
Yeah, P-NTRs can easily be made into Bimodal systems. Though the power would come in rapid pulses and not continuously.
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Post by Phoboshine on Feb 12, 2017 13:23:31 GMT
I like this pulsed solid NTR. But I have a doubt. If Isp is produced by a pulse, then the maximun Isp is not limited by radiative heat transfer, because the temperature at the pulse will be inmense and then will decay very fast. But in other rockets the propellant is heated continuously from cold to hot and then never will reach very high temperatures, say 20000 K. In other words the problem with the propellant in the pulsed solid NTR would be that it must be ejected from the rocket as soon as possible or will be cooled very fast. At 20000K or 30000 K radiative heat transfer is very strong Since this is all happening within a reaction chamber, and the pulses are spaced rather closely together, wouldn't radiative transfer and conduction simply result in a sort of dampening in average temperature? That would be the case if the propellant spends more than 1 period inside the engine. This would, of course, bring the average temperature down quite a bit. But "quite a bit" is a relative term and the Isp would still blow everything we currently have out of the water. I don't think anyone has fully done the, math, however. I wish I understood nuclear reactors well enough to make an attempt, but alas, I am hardly beyond an informed layman on the topic. This could be, but conduction is very inefficient in comparison with radiation at 200000K or more. In any case, the velocity of hydrogen at, say, 20000 K or more will be very very high, so, with a chamber of, 1 meter or less, the propellant will have not time to loss heat (velocity) by conduction which requires times in the order of 0.1 seconds or thereabouts. The only problem is radiation which travels at speed of light. But then come my question, if the pulsed solid NTR need short time of residence in the chamber as soon is heated by the pulse. Then, in this kind of concept, it is really useful the nozzle? I mean, a nozzle only increases the velocity, I think a factor 1.8 as theoretical maximum value, but, if you are eliminating the nozzle, perhaps you loss this 1.8 factor but you will gain, say a factor 3 or so because you are reducing the time of the propellant in the rocket. For example. If the Isp is, say, a discrete 3000 sec (I am reading above that could be 15000 Isp!, but even with 3000 Isp a rocket engineer will be happy, I suppose), then the velocity will be on 30km/second, thus in just a millisecond will travel 30 meters. If the chamber is on 1 meter only will last 1/30 of second in the rocket, not much time for conduction ok, but for radiation it will be high. So reducing the time in the chamber means reducing the length of the core, and why not eliminating the nozzle?? After all, in the concept the heating is by a pulse not by trasnporting the propellnat for a warm surface and extracting heat form top to bottom. |
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Post by Teseous1992 on Feb 12, 2017 13:27:42 GMT
I like this pulsed solid NTR. But I have a doubt. If Isp is produced by a pulse, then the maximun Isp is not limited by radiative heat transfer, because the temperature at the pulse will be inmense and then will decay very fast. But in other rockets the propellant is heated continuously from cold to hot and then never will reach very high temperatures, say 20000 K. In other words the problem with the propellant in the pulsed solid NTR would be that it must be ejected from the rocket as soon as possible or will be cooled very fast. At 20000K or 30000 K radiative heat transfer is very strong Since this is all happening within a reaction chamber, and the pulses are spaced rather closely together, wouldn't radiative transfer and conduction simply result in a sort of dampening in average temperature? That would be the case if the propellant spends more than 1 period inside the engine. This would, of course, bring the average temperature down quite a bit. But "quite a bit" is a relative term and the Isp would still blow everything we currently have out of the water. I don't think anyone has fully done the, math, however. I wish I understood nuclear reactors well enough to make an attempt, but alas, I am hardly beyond an informed layman on the topic. |
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Post by Teseous1992 on Feb 12, 2017 13:28:27 GMT
This could be, but conduction is very inefficient in comparison with radiation at 200000K or more.
In any case, the velocity of hydrogen at, say, 20000 K or more will be very very high, so, with a chamber of, 1 meter or less, the propellant will have not time to loss heat (velocity) by conduction which requires times in the order of 0.1 seconds or thereabouts. The only problem is radiation which travels at speed of light.
But then come my question, if the pulsed solid NTR need short time of residence in the chamber as soon is heated by the pulse.
Then, in this kind of concept, it is really useful the nozzle?
I mean, a nozzle only increases the velocity, I think a factor 1.8 as theoretical maximum value, but, if you are eliminating the nozzle, perhaps you loss this 1.8 factor but you will gain, say a factor 3 or so because you are reducing the time of the propellant in the rocket. For example. If the Isp is, say, a discrete 3000 sec (I am reading above that could be 15000 Isp!, but even with 3000 Isp a rocket engineer will be happy, I suppose), then the velocity will be on 30km/second, thus in just a millisecond will travel 30 meters. If the chamber is on 1 meter only will last 1/30 of second in the rocket, not much time for conduction ok, but for radiation it will be high. So reducing the time in the chamber means reducing the length of the core, and why not eliminating the nozzle?? After all, in the concept the heating is by a pulse not by transporting the propellant for a warm surface and extracting heat form top to bottom.
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