External Fuel Duct Cooling ?

[Gaarst]

I am currently working on a nuclear powered ship that needs external fuel ducts between the tanks and the engine, as below:

Then I thought that, as there were big heating issues with 1.0 (less with 1.0.2), it might be a good idea to add a feature that makes the fuel passing through these ducts cooled while in space.

This would happen because the ducts are directly exposed to the coldness of space. So, for example, the longer the duct, the cooler the fuel.

Cold fuel being consumed in the engine could then cool it down or reduce its heat output (just like real rockets) as long as the engine is active (so that there is actual fuel flow).

Though this might not be necessary with 1.0.2, it could be a good thing to reintroduce more realistic heating, while having actual ways to manage it without adding any stock or modded parts to your rocket.

I think it could be good thing to consider and that it could lead to interesting rocket designs to manage heat other than just an engine stacked to a tank, where the fuel would go directly from the tank to the engine without being cooled through the ducts.

[Jason_25]

This wouldn't work very well because of the 3 forms of heat transfer, only radiation usually works in space. Your fuel being pumped won't be in the "coldness" of space for long enough to make much difference.

[DancesWithSquirrels]

Important - only one of your tanks is connected to the inverted tri-coupler!

The KSP basic part tree branches, but doesn't converge (1->N, not N->1), so two of your tanks are going to just be hanging there. You need to strut or fuel-line them to the inverted coupler to get a solid connection for all three. This is the same problem that people used to have when building large ships in orbit with tri- or quad-couplers and multiple docking ports prior to the Clamp-O-Tron Sr - converging connections weren't made.

Now, for fuel flow, the 'plane' of the tri-coupler that blocks inverted flow is the 3-connection side. If you plumb fuel lines to the coupler itself, you can get fuel flow out the single connection at the bottom, as in this (quite old) test vehicle of mine. The fuel lines act as struts to hold it together, and now all three tanks drain simultaneously (not just one).

http://imgur.com/mlb79Wx

Edited May 7, 2015 by DancesWithSquirrels

[Gaarst]

Important - only one of your tanks is connected to the inverted tri-coupler!

The KSP basic part tree branches, but doesn't converge (1->N, not N->1), so two of your tanks are going to just be hanging there. You need to strut or fuel-line them to the inverted coupler to get a solid connection for all three. This is the same problem that people used to have when building large ships in orbit with tri- or quad-couplers and multiple docking ports prior to the Clamp-O-Tron Sr - converging connections weren't made.

Now, for fuel flow, the 'plane' of the tri-coupler that blocks inverted flow is the 3-connection side. If you plumb fuel lines to the coupler itself, you can get fuel flow out the single connection at the bottom, as in this (quite old) test vehicle of mine.

Thank you for this, but I already noticed it myself when there weren't any struts (that did not end well) but the struts and ducts are enough to maintain the tanks or engine in their place.

And I prefer the ducts to be from the tanks to the engine directly as it makes the whole engine-coupler-tank link more rigid instead of just coupler-tank link and having the coupler-engine link weaker.

[DancesWithSquirrels]

Good to hear - I would personally add some additional tank-tricoupler struts, just to make the whole thing more rigid.

Edited May 7, 2015 by DancesWithSquirrels
Better Engrish.

[Kuu Lightwing]

space is not cold, it's just empty and full of nothing. When in space, you can only radiate heat and fuel ducts aren't good radiators, so this probably won't work well.

Also, you don't want to cool NERVA too much, since it needs to run hot to be efficient. Everything around it needs cooling, of course.

[LordFerret]

Important - only one of your tanks is connected to the inverted tri-coupler!

The KSP basic part tree branches, but doesn't converge (1->N, not N->1), so two of your tanks are going to just be hanging there. You need to strut or fuel-line them to the inverted coupler to get a solid connection for all three. This is the same problem that people used to have when building large ships in orbit with tri- or quad-couplers and multiple docking ports prior to the Clamp-O-Tron Sr - converging connections weren't made.

Now, for fuel flow, the 'plane' of the tri-coupler that blocks inverted flow is the 3-connection side. If you plumb fuel lines to the coupler itself, you can get fuel flow out the single connection at the bottom, as in this (quite old) test vehicle of mine. The fuel lines act as struts to hold it together, and now all three tanks drain simultaneously (not just one).

http://i.imgur.com/mlb79Wx.jpg

http://imgur.com/mlb79Wx

Absolutely this ^

As for the struts, not only do I strut the fuel tanks to the inverted tri-coupler, I strut them to each other.

[itstimaifool]

(This has already been mentioned, but I'm going to go into a little more detail)

There's some common misconceptions about space and heat. First of all, let's define heat: Heat is the vibration of atoms within a material. If something is hotter, then the atoms vibrate more. Space doesn't have any atoms to vibrate, so it doesn't have a temperature.*

Stuff can be cooled by two methods**: Conduction and Radiation. Conduction is the transfer of heat by contact: When a hot thing is in contact with a cold thing, the atoms vibrating very energetically in the hot thing tend to smash into the atoms vibrating slowly in the cold thing. These collisions slow down the atoms in the hot thing and speed up the atoms in the cold thing. As a result, heat moves out of the hot thing and into the cold thing.

Radiation is heat transfer without physical contact. When things get hot, they glow. This is obvious in things like lava and molten metal, but it's true of everything. Humans are hot enough to glow in infrared, which can be seen with special cameras. Energy is needed to make this glow happen, though. This energy comes from the heat of the object. Therefore, the heat of an object will gradually decrease as it is turned into light and escapes. This is how things cool in space, since there is no material to be in contact with.

This is why solar panels and wings make good radiators and fuel lines don't: They have much more surface area, which means much more area that can glow, which means more energy is able to escape as light***.

Also, it's already been mentioned, but nuclear engines need to be hot to run, and even if you feed it cold fuel, it's specifically designed to heat up fuel to ridiculous temperatures anyway, so it won't make much difference.

*Technically, there's a little bit of dust and gas drifting through space, but it's little enough that it doesn't really matter.

**I think it's technically three. Convection, which is heat transfer by moving fluids, being the third. But I don't quite understand how this is different from conduction, so I'm lumping it in with conduction.

***There's also other factors, like the material they're made of, but I don't know much about this, so I'll just leave it at that.

[Gaarst]

@itstimaifool (and others)

Thank you for your reply

I was just telling this as an idea I got spontaneously and I know that in space the only efficient way to cool is through radiation. What I said is not physically accurate as fuel ducts indeed have poor radiating area and would not cool fuel efficiently.

FYI: conduction does not involve displacement of matter but collisions between the vibrating atoms themselves, that's why it is more efficient with solids. Convection on the other hand requires matter displacement: hotter particles move around amongst cooler ones and make the overall temperature homogeneous without really transmitting it to other particles, that's why it is more efficient in fluids (liquids or gases).

And radiation depends on the area exposed, the emissivity of the material and (a LOT) on the temperature difference between the hotter and cooler materials.