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Post by ross128 on Nov 14, 2016 17:03:24 GMT
Regarding the coolant thing, there are several factors that go into being a good coolant.
A high specific heat is generally desirable, because a higher specific heat will give you a greater temperature change in the system being cooled for a smaller temperature change in the coolant (resulting in a lower overall temperature at equilibrium).
High thermal conductivity is also desirable, because that's how fast the heat gets out of the core and into the coolant (or out of the coolant and into space on the radiators' end). Of course you want the coolant to be either a liquid or gas at its operating temperature so the pump will work, preferably liquid due to the next point (gasses are better for phase-change or compression systems, but we're not using those in-game).
A high density is desirable because specific heat is measured per unit mass. Higher density, more mass of coolant in a smaller area.
Sodium fills many of these: it's a liquid at fairly high temperatures (though its boiling point is 1156K, so 2000K+ probably use gaseous sodium), it has a density similar to water, it's very thermally conductive, and has a pretty good specific heat (though water's is three times higher). The high conductivity and better tolerance of high operating temperatures are what likely give it the edge over water in-game, since water has it soundly beat on specific heat.
At the temperatures some of our reactors run at, we could probably get away with using molten aluminum. It has only two thirds of the specific heat of sodium, but nearly double the conductivity and double the density to make up for it. We'd have to make sure no part of the loop it's in goes below 933K though, so we'd probably only be able to use it in the inner loop.
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Post by wafflestoo on Nov 14, 2016 17:54:24 GMT
Molten aluminum as a coolant... I really need to stop sneaking peaks at these forums while I'm at work. Now I'm going to be obsessing over that all day until I can get home and experiment with it. XD
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Post by ross128 on Nov 14, 2016 18:00:04 GMT
Alas, I don't think aluminum is on the coolant list in-game.  |
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Post by someusername6 on Nov 14, 2016 18:11:55 GMT
Well here are we suggesting / requesting it as a feature then.
I want to play with molten metals in my reactors please.
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Post by tessfield on Nov 14, 2016 20:32:59 GMT
Whoa xD I'll have to read up on quite a few things and try to wrap my head around it. Re: Molten Aluminum: Let's not forget we can add that by simply editing a text file (and I will do that if nobody beats me to it) I believe the game doesn't let you use a coolant if it'd be solid either, so you can't even cheat with it (could be wrong). Re: Cooling: I don't understand one thing though, the thermocouple displayed has the same temperature difference, but creates different voltage differences. What's not being displayed in the graph? Or perhaps I am misunderstanding how a thermocouple works? Is it not just the temperature difference that matters? |
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Post by Pttg on Nov 14, 2016 22:10:55 GMT
I would love to have some molten aluminum coolant. Might be good to add gallium and lead while we're at it... wasn't there a real-world reactor with lead coolant?
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Post by wafflestoo on Nov 14, 2016 22:50:58 GMT
Whoa xD I'll have to read up on quite a few things and try to wrap my head around it. Re: Molten Aluminum: Let's not forget we can add that by simply editing a text file (and I will do that if nobody beats me to it) I believe the game doesn't let you use a coolant if it'd be solid either, so you can't even cheat with it (could be wrong). Re: Cooling: I don't understand one thing though, the thermocouple displayed has the same temperature difference, but creates different voltage differences. What's not being displayed in the graph? Or perhaps I am misunderstanding how a thermocouple works? Is it not just the temperature difference that matters? It's the differing power requirements for the turbopumps that alter the net power output. Some coolants (hydrogen) are easier to pump than others (molten sodium). |
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Post by tessfield on Nov 15, 2016 1:40:44 GMT
<snip> It's the differing power requirements for the turbopumps that alter the net power output. Some coolants (hydrogen) are easier to pump than others (molten sodium). While that is a factor, it doesn't look to be the factor. There are many things going on. One of them is how good the coolant is as a neutron reflector, which affects the fission reaction of the core. Which in turn affects everything else. I'd love to be able to read these things out of the coolant materials properties (ie roughly kinda estimate), there's just so many factors...  I am most likely wrong about this, but if I vaguely understand the concepts involved, are these the ones to look into? Density
| This will affect how good a neutron moderator the coolant will be. I thiiiink this is meaningless if you're looking at it purely from a coolant only perspective since it's effects are included into the other coefficients...?
| Specific Heat
| Heat "capacity" of material | Viscosity
| Something about laminar vs turbulent flow in the cooling pipes depends on viscosity...? I'm not sure what applies to the simulation.
Water is less viscous than honey.
I assume more viscosity is better for easier/faster(? less power needed on the pump?) travel of the coolant through the pipes.
| Thermal Conductivity
| Heat "absorption" rate of material
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All in all, I still don't understand what the graphic is trying to show, all I see is this: Internal
Coolant
(HOT!) Thermocouple
Hot End
(HOT) Electricity
Relative To
<< dT >>
Themocouple
Cold End
(COLD) External
Coolant
(COLD!) (Of course cold is relative when it's 2500K ) And while I can understand that different coolants would need different flow rates/pump power to transfer heat to/from the thermocouple, the way I understand the graph, we're being shown that the temperature difference in the thermocouple hasn't changed. However, when we increase the flow AND the thermal energy generated by the reactor (ie neutron flow and say, pump size), the thermocouple, somehow, starts generating more electricity. And THAT is what I don't understand  (Should I move this to its own thread? ie.: "Understanding Thermocouples and Coolants"? Perhaps under General Discussion?) |
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Post by amimai on Nov 15, 2016 3:22:59 GMT
ok after some looking around at various material stats here is what to look for
thermal conductivity : this stat is GOD, it determines how fast the coolant can go through the pipes and how efficient it is at actually cooling stuff
this is what makes sodium such a good coolant, you can run 1m^3 of sodium at 5x the speed of ethane through the pipes and get the same result
sidenote: this also seems to effect thermocouple stress, higher values allow larger dT across the couple, particularly obvious in high temperature reactors
(sodium vs ethane)
specific heat : the ability of a coolant to hold heat per kg
this is why mercury while being one of the 3 viable high temperature coolants is not useful, it simply takes tones to hold all the necessary heat
(mercury vs oxygen)
density * specific heat : this determines how much heat a coolant can hold per m^3
this is why mercury can be used as a coolant, the pump can actually pump enough of it through to take out all the necessary heat
(mercury vs oxygen)
viscosity/speed of sound : seems to have no real effect
so basically you want a:
high temperature conductor so it can pick up and dump heat
with high specific heat, so you can use less of it
and high density, so you can pump more of it with a smaller system
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Post by ross128 on Nov 15, 2016 14:08:51 GMT
As far as viscosity goes, lower viscosity is technically better because a "thinner" fluid will get a higher flow rate with less pump power (imagine the difference between pumping water, honey, or peanut butter). However, it is generally sacrificed in favor of other favorable attributes, for example it tends to be inversely proportional to density, which is also desirable if you want a compact system. And the good thermal conductors tend to be metals, which you'd be using for their ridiculously high conductivity more than anything else.
If someone discovered a material with almost all of the physical properties of water, but the thermal conductivity of copper (which is also liquid at our reactor temperatures, but probably wouldn't make a good coolant due to its pitiful heat capacity of just 384 J/kg), that would probably be an almost ideal coolant.
No one material (that I know of) is able to top the charts on all of the desirable qualities at the same time, so it's a matter of balancing the trade-offs between them to find the best overall outcome.
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Post by aetreus on Nov 17, 2016 0:12:15 GMT
For those of you wondering how realistic our reactors are, the answer is more than you'd think. The USSR's BES-5 reactor had a core of only 53 kg and a total system mass of only 386kg, and generated 3kW of electrical power from 100kW of heat. Obviously that's a lot worse than these, but we have the advantages of working right at the material limits(while real reactors generally have generous safety margins) and using materials that have much better properties.
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Post by dragonkid11 on Nov 17, 2016 1:55:47 GMT
That, and we can have even worse safety margin than Soviet Russia because spaceeeeee.
Make you wonder if cancer is just plain cured in the CoaDE because space is full of radiation.
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Post by apophys on Nov 17, 2016 15:00:08 GMT
Make you wonder if cancer is just plain cured in the CoaDE because space is full of radiation. O.o Radiation causes damage to molecules, such as DNA. Low-level radiation causes enough damage for cancer. High-level radiation will outright kill things. High-level radiation is used to treat cancer by focusing on it and killing the existing cancer cells. If the entire human were exposed to high-level radiation, the entire human would be dead. Do notice that in the process of focusing high-level radiation on a tumor, the surrounding tissue is exposed to low-level radiation. Thus the surrounding tissue becomes more likely to generate a fresh new cancer. It's considered an acceptable risk. Surgery (i.e. cutting it out), if possible, is a far better option. |
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Post by jonen on Nov 17, 2016 15:14:21 GMT
I parsed the cancer thing as "if cancer wasn't cured, everyone would have it, because space is full of cancer causing radiation".
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Post by apophys on Nov 17, 2016 15:51:27 GMT
Regarding coolants, I want to see liquid lithium. From my understanding, raw density is not a pro, but a con, due to increasing the mass of the system. Density is only important in terms of heating per volume, as density * specific heat. Lithium has high enough specific heat compared to everything else that the low density shouldn't hinder it mechanically, while providing substantial mass savings. I parsed the cancer thing as "if cancer wasn't cured, everyone would have it, because space is full of cancer causing radiation". That kind of thought didn't occur to me, because of how easy shielding appears to be. |
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