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Post by ironclad6 on Sept 6, 2017 16:45:49 GMT
So I've got a 4600K thermocouple, a ~10000K plasma and a nozzle at 330 million K according to CDE. I need separate radiators for all three (Accounted for) The plasma is 330 million K, this heat mostly flies away with the fusion fuel, a small percentage radiates at your blade shields (the thermocouple in this case). Having 4600K Coolant. The problem is you can't make 4600K to 10000K with heat exchanging. An heat exchanger tries to raise the temperature until both are the same temperature. Your plasma radiators can only reach 4600K at max. This is entropy. You can't revert chaos and unorder in a closed system (Universe/your ship) but you can keep it constant. So I don't actually have to account for back scatter or cooling my the blade armature my magnetic nozzle sits on? |
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Post by The Astronomer on Sept 6, 2017 16:46:57 GMT
Then there's me, trying to understand where this thread is going.
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Post by Kerr on Sept 6, 2017 16:48:10 GMT
The plasma is 330 million K, this heat mostly flies away with the fusion fuel, a small percentage radiates at your blade shields (the thermocouple in this case). Having 4600K Coolant. The problem is you can't make 4600K to 10000K with heat exchanging. An heat exchanger tries to raise the temperature until both are the same temperature. Your plasma radiators can only reach 4600K at max. This is entropy. You can't revert chaos and unorder in a closed system (Universe/your ship) but you can keep it constant. So I don't actually have to account for back scatter or cooling my the blade armature my magnetic nozzle sits on? What? What I meant is you can't practically get an lower temperature coolant to give off heat to an higher temperature coolant. |
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Post by Kerr on Sept 6, 2017 16:49:13 GMT
Then there's me, trying to understand where this thread is going. It kinda became the universal hypothetical high tech technology thread. |
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Post by ironclad6 on Sept 6, 2017 16:51:04 GMT
Then there's me, trying to understand where this thread is going. : Your input please? Yeah. I have no idea either. I apologize. I don't actually know what's being required of me. Edit to add: As I see it, it's incoherent to permit magnetic confinement fusion while disallowing dusty plasma radiators. Ultimately these applications of the same technology. If you do away with magnetic confinement but you still want fusion power you are actually better off with MPDT. You can't have high thrust open cycle fusion without having dusty plasma or some equivalent. Therefore the heat I need to dispose of at the highest possible temperature is 1) Back scatter from my thrust plume. 2) Excess heat due to inefficiency at the low end of the thermocouple in my fusion reactor. 3) The superconducting coil and blade armature maintaining the EM field that makes my fusion rocket possible. Can anyone tell me where I am wrong? |
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Post by matterbeam on Sept 7, 2017 1:58:35 GMT
Then there's me, trying to understand where this thread is going. : Your input please? Yeah. I have no idea either. I apologize. I don't actually know what's being required of me. Edit to add: As I see it, it's incoherent to permit magnetic confinement fusion while disallowing dusty plasma radiators. Ultimately these applications of the same technology. If you do away with magnetic confinement but you still want fusion power you are actually better off with MPDT. You can't have high thrust open cycle fusion without having dusty plasma or some equivalent. Therefore the heat I need to dispose of at the highest possible temperature is 1) Back scatter from my thrust plume. 2) Excess heat due to inefficiency at the low end of the thermocouple in my fusion reactor. 3) The superconducting coil and blade armature maintaining the EM field that makes my fusion rocket possible. Can anyone tell me where I am wrong? You simple need the physical components of your 'energy chain' between the fusion reaction and your radiator to stay within solid material temperature limits. Starting from the blade armature: it will intercept some of the electromagnetic energy leaking from a fusion reaction. The point of having blades is so that this energy is a very small percentage of the engine power. The external surface of the blades must be kept under 4600K or it is melting away. This means you are running coolant from the radiators at a cool 300K, passing it over the sizzling blades and returning it to the radiators at under 4600K. This is the first source of waste heat. You then have the electromagnets inside the blades. The blades are just housing for these coils. If they are superconductive, which they are very likely to be, then they need to cooled down to 100K or less. They will absorb heat leaking inwards from the blades at 4600K. This heat is carried away by a coolant... at 100K. Obviously, it will take incredibly large radiators to deal with even this small amount of heat. You therefore need heat pumps. A heat pump pushing waste heat up from 100K to your radiator's operating temperature will consume a lot of electricity, but it will be necessary. If your radiators operate at 3000K, then you need (3000-100)/100:29W of electricity to move 1W of waste heat at a minimum. Then there is the electrical generator. It can be a simple thermocouple that uses the blades as a 4600K hot end and the radiators as a cold end. You want a big temperature difference to extract a lot of energy, but also a higher temperature cold end to reduce radiator size. Thermocouples are also terribly inefficient and create waste heat at their cold end temperature. So, you need more radiators at the cold end temperature. If you use much more efficient magnetohydrodynamics, you reduce the amount of waste heat but it will come at the generator's operating temperature. This can be as low as 380K for conventional electronics. You'd need heat pumps to move the waste heat from 380K to your radiator temperature... My point is, even if your fusion reaction happens at millions of Kelvin, your radiators will operate far below the maximum melting point of the blades. From the energy you extract, a lot of it winds up being wasted in keeping the components cool through heat pumps. Backscatter shouldn't be a problem when your fusion reaction happens inside of a propellant cloud. |
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Post by Enderminion on Sept 7, 2017 2:47:43 GMT
wouldn't the heat pump create heat at the temp of it's inlet temp?
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Post by Kerr on Sept 7, 2017 11:16:35 GMT
wouldn't the heat pump create heat at the temp of it's inlet temp? Either that or lower temp. |
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Post by matterbeam on Sept 7, 2017 11:59:51 GMT
wouldn't the heat pump create heat at the temp of it's inlet temp? Yeah, heat pumps aren't 100% efficient, so you'll need more watts consumed to move 1W of waste heat, and the difference is released as electronics level waste heat (380K). If the 3000 to 100K cryogenic heat pump was only 75% efficient, it would use 29 W to move 1W of 100K heat, and produce 9.7W of 380K heat. |
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Post by The Astronomer on Sept 7, 2017 12:19:43 GMT
wouldn't the heat pump create heat at the temp of it's inlet temp? Yeah, heat pumps aren't 100% efficient, so you'll need more watts consumed to move 1W of waste heat, and the difference is released as electronics level waste heat (380K). If the 3000 to 100K cryogenic heat pump was only 75% efficient, it would use 29 W to move 1W of 100K heat, and produce 9.7W of 380K heat. AKA heat pumps won't work... EDIT: ...at very high T difference. |
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Post by Kerr on Sept 7, 2017 12:21:55 GMT
Yeah, heat pumps aren't 100% efficient, so you'll need more watts consumed to move 1W of waste heat, and the difference is released as electronics level waste heat (380K). If the 3000 to 100K cryogenic heat pump was only 75% efficient, it would use 29 W to move 1W of 100K heat, and produce 9.7W of 380K heat. AKA heat pumps won't work... AKA Heat pumps suck at extreme temperature differences. |
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Post by matterbeam on Sept 7, 2017 16:00:25 GMT
@astrogator: They do work and are completely necessary on warships requiring lots of power out of low-temperature components. The biggest obstacle to laser weaponry today is heat. Not power, heat. This is because we are pushing for fibre lasers with maybe a 400K maximum working temperature, to handle megawatts of electrical input. In space, the same will happen. High efficiency lasers work at low temperatures. COADE muddles the picture a bit by allowing lasers to work at incredibly high 2000K temperatures and not including any sort of heat pump. Kerr : That's thermodynamics for you! Although, the waste heat being dealt with is pretty low. I like to divide waste heat into high, mid and low-grade. High-grade waste heat is at a higher temperature than your main radiator. Just run a heat exchanger between the two. Mid-grade heat operate at lower temperatures than your radiator. You might need a secondary radiator system for this heat. Low-grade heat is far below any practical radiator temperature. You need heat pumps to move it up to practical temperatures. Keeping with my example, good insulation between the blade edges and the cryo-cooled superconducting magnets inside can reduce heat leaking into a mere fraction of what the blades absorb, itself a tiny percentage of the fusion blast. Blades can intercept 1% of the fusion blast's energy. This is absorbed as heat. If the interior of the blades has a vacuum gap and a 95% reflective coating on the inside, then 5% of the half of the heat being radiated inwards is absorbed by the magnets. The total fraction of fusion energy absorbed by the magnets is 0.025%. Let's set your low-grade waste heat removal capacity at 10MW. This requires the heat pumps to be fed with 387MW of electrical power, of which 97MW becomes mid-grade heat. Blades intercept only electromagnetic and neutral emissions, which is the fraction of fusion power that is not contained in the kinetic motion of the propellant cloud. It depends mostly on the type of fusion reaction and whether you are lowering the temperature by using 'afterburner' propellant. A pure fusion D-He3 rocket releases 25% of its energy as X-rays and neutrons. If 10MW represents 0.025% of your X-ray fusion leftovers, then you can run the engines as high as 16GW. You'd need to capture 387MW from the thermal fusion power (75%) to break even with your cooling needs, which is 3.2% of 12GW. Use this : www.projectrho.com/public_html/rocket/fusionfuel.php#reactionsIf we go to even more extreme specifications, we can use reflective coatings on the blades, smaller blades, large distances between the blades and the fusion reaction or and special multi-layered reflective coatings inside the blades to reflect more of the inward-radiating heat away from the superconducting magnets. This allows for even greater fusion power levels. Good luck, however, with producing sufficiently strong magnetic fields from coils inside thinner, longer and more distant blades filled with insulation. A balance must be struck. If I were ironclad6 , I wouldn't attempt to try to find exact geometric definitions of how much energy the blades intercept, the ablation rates from initial burst of blackbody radiation before the plasma expands, the stress handling requirements from when the plasma pushes back against the magnetic coils or the average temperature of the blade materials during operation. Just say they glow white-hot, the energy intercepted is a realistic figure like 0.01% and move onto more interesting things. |
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Post by Kerr on Sept 7, 2017 18:06:55 GMT
@astrogator: They do work and are completely necessary on warships requiring lots of power out of low-temperature components. The biggest obstacle to laser weaponry today is heat. Not power, heat. This is because we are pushing for fibre lasers with maybe a 400K maximum working temperature, to handle megawatts of electrical input. In space, the same will happen. High efficiency lasers work at low temperatures. COADE muddles the picture a bit by allowing lasers to work at incredibly high 2000K temperatures and not including any sort of heat pump. Kerr : That's thermodynamics for you! Although, the waste heat being dealt with is pretty low. I like to divide waste heat into high, mid and low-grade. High-grade waste heat is at a higher temperature than your main radiator. Just run a heat exchanger between the two. Mid-grade heat operate at lower temperatures than your radiator. You might need a secondary radiator system for this heat. Low-grade heat is far below any practical radiator temperature. You need heat pumps to move it up to practical temperatures. Keeping with my example, good insulation between the blade edges and the cryo-cooled superconducting magnets inside can reduce heat leaking into a mere fraction of what the blades absorb, itself a tiny percentage of the fusion blast. Blades can intercept 1% of the fusion blast's energy. This is absorbed as heat. If the interior of the blades has a vacuum gap and a 95% reflective coating on the inside, then 5% of the half of the heat being radiated inwards is absorbed by the magnets. The total fraction of fusion energy absorbed by the magnets is 0.025%. Let's set your low-grade waste heat removal capacity at 10MW. This requires the heat pumps to be fed with 387MW of electrical power, of which 97MW becomes mid-grade heat. Blades intercept only electromagnetic and neutral emissions, which is the fraction of fusion power that is not contained in the kinetic motion of the propellant cloud. It depends mostly on the type of fusion reaction and whether you are lowering the temperature by using 'afterburner' propellant. A pure fusion D-He3 rocket releases 25% of its energy as X-rays and neutrons. If 10MW represents 0.025% of your X-ray fusion leftovers, then you can run the engines as high as 16GW. You'd need to capture 387MW from the thermal fusion power (75%) to break even with your cooling needs, which is 3.2% of 12GW. Use this : www.projectrho.com/public_html/rocket/fusionfuel.php#reactionsIf we go to even more extreme specifications, we can use reflective coatings on the blades, smaller blades, large distances between the blades and the fusion reaction or and special multi-layered reflective coatings inside the blades to reflect more of the inward-radiating heat away from the superconducting magnets. This allows for even greater fusion power levels. Good luck, however, with producing sufficiently strong magnetic fields from coils inside thinner, longer and more distant blades filled with insulation. A balance must be struck. If I were ironclad6 , I wouldn't attempt to try to find exact geometric definitions of how much energy the blades intercept, the ablation rates from initial burst of blackbody radiation before the plasma expands, the stress handling requirements from when the plasma pushes back against the magnetic coils or the average temperature of the blade materials during operation. Just say they glow white-hot, the energy intercepted is a realistic figure like 0.01% and move onto more interesting things. Awesome post and good math, but is the 0.01% the absorbed heat is for the blade shields or the magnets? For ironclad6's 5PW Fusion Drive the amount of waste heat the "system" has to deal with is 500GW. Which either means we have to operate 100t Hydrogen (or anything with a similar specific heat) at 300K to remove 500GW waste heat, this assumes that the heat just perfectly jumps from the coils to the coolant. If you meant the blade shields the waste heat drops drastically. using an 99% Reflective coating we will only have to deal with 2.5GW. requiring roughly a ton of coolant. Most decent Fusion torch drives would look kinda similar to the fusion drive of the firefly. Letting most radiation escape into space, use very thin coils and sharp blade shields and using an angled bottom to reflect X-rays As a side note, I've used this link to often back then when I made my firefly and when helping Astrogator with realistic fusion that I nearly memorized the entire chart.... But thanks for trying to share Project Rho links. I also found out that the bremsstrahlung power exceeds the fusion power by 1.75x in proton-boron fusion. Resulting in 36% Thermal power and 64% X-rays. |
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Post by matterbeam on Sept 7, 2017 23:39:47 GMT
Awesome post and good math, but is the 0.01% the absorbed heat is for the blade shields or the magnets? For ironclad6's 5PW Fusion Drive the amount of waste heat the "system" has to deal with is 500GW. Which either means we have to operate 100t Hydrogen (or anything with a similar specific heat) at 300K to remove 500GW waste heat, this assumes that the heat just perfectly jumps from the coils to the coolant. If you meant the blade shields the waste heat drops drastically. using an 99% Reflective coating we will only have to deal with 2.5GW. requiring roughly a ton of coolant. Most decent Fusion torch drives would look kinda similar to the fusion drive of the firefly. Letting most radiation escape into space, use very thin coils and sharp blade shields and using an angled bottom to reflect X-rays As a side note, I've used this link to often back then when I made my firefly and when helping Astrogator with realistic fusion that I nearly memorized the entire chart.... But thanks for trying to share Project Rho links. I also found out that the bremsstrahlung power exceeds the fusion power by 1.75x in proton-boron fusion. Resulting in 36% Thermal power and 64% X-rays. The 0.01% is what reaches the cryogenic superconducting coils. Sorry for linking the fusion fuels page again. It's a reflex to source my claims  How did you find out about proton-boron's bremsstrahlung power percent? |
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Post by ironclad6 on Sept 7, 2017 23:44:28 GMT
TBH this is actually making me not want to write this novel. I feel bad for having de-railed this thread too. Is there any chance we can get this split out from the original thread?
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