Can radiator fins face each other?

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Deus Siddis
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Can radiator fins face each other?

Post by Deus Siddis »

This is a canon and realism question that has an obvious effect on official artwork design.

Can the broadsides of radiator fins face each other (or at least be less than 90 degrees apart)?

Is this inefficient or not really a problem in space? Do diffuse surfaces solve any problems? Or would isosceles right trangular grooves in the surface be enough to keep radiation from being passed back and forth between the two parallel fins?
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Post by chuck_starchaser »

The radiator fins on the nuclear fuel cells of the craft that went to Saturn, forget the name now, are 60 degrees apart. The fuel cells are cylindrical and have 6 longitudinal fins around. A bit more than 60 degrees, actually, as the fins taper outwards. But that's the sharpest angle I've seen in space rads. More often they are flat planes, like the ones on the ISS, and the ones lining the inside of the doors on the shuttle. Color varies: Usually black; but the shuttle's rads look like gold-plated.
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Post by jackS »

From what material I can find on the subject, they can be less than 90 degrees apart, but it will reduce per-fin efficiency - you aren't getting as much bang for your buck on the additional fins. However, you do get redundancy, which is somewhat important for craft that you expect to get shot at frequently, especially since, with two exceptions, radiators are really hard to protect from damage. Both of these exceptions have their own problems:

Exception A) Open-cycle cooling: you can get rid of heat very quickly and without much additional equipment by dumping your coolant. Obvious problem - you don't have the coolant anymore. This can make a lot of sense for emergency overheat scenarios, single-use craft (i.e. missiles), or as a cooling solution for limited-fire high-energy weapon-systems, but it's completely impractical for ship-wide normal cooling.

Exception B) Droplet/particle radiators: rather than a huge, radiator sail that can't be armored, you have huge expanse with an array of nozzles on one end and collectors on the other. The droplets provide the radiating surface area. You can't armor a sheet of droplets of liquid metal, but by the same token, shooting said sheet of droplets doesn't exactly damage it. Obvious problems - even when using liquid metals with very low vapor pressures, you're going to lose some of your coolant due to evaporation. Moreover, if your craft is accelerating while this system is in use, depending on the direction of acceleration and the configuration of the droplet system, you could lose a LOT of your coolant.

Military and civilian ships are going to have rather different approaches to radiators and internal heat sinks. Civilian craft have heat sinks as buffers for ephemeral or unexpected mismatches (part failure, unplanned maneuvers, etc.) between their ability to dissipate heat and their normal generation thereof. Military craft need heat sinks to perform unsustainable maneuvers and weapon attacks. There is a much bigger gap for military vessels between peak combat performance and normal cruising behavior than for civilian craft. Likewise, the military craft need to be designed to expect damage to radiator surfaces, so the internal heatsink is relied upon to provide for much more graceful degradation of capabilities than the almost hand-to-mouth cooling solutions used in less expensive craft.

You can expect there to be multiple types of radiators active under different scenarios. The droplet radiators, for instance, while not useful during combat, will likely survive said combat in better shape than exposed radiator fins, and can be used to re-cool the heat sink once combat has terminated. Single surface radiators (hull-insets) can be covered with retractable covers and serve a similar purpose. You can pull a related trick with hinged armor coverings and fins, but I won't try to draw it with asciii, and suffice it to say that covering up your radiator surfaces only makes sense if you're a sufficiently large vessel that having a side away from the enemy (on which to keep radiators active) is a vaguely meaningful statement. You may also see distributed networks of small-surface radiator segments built into/on top of large portions of the hull/armor surface -- these aren't designed to be efficient so much as ubiquitous, compartmentalized, and highly redundant, they're just there for graceful degradation, so as to keep the vessel from having to shut down completely (just go into low-power mode) when the primary radiators become excessively damaged. Shutting down completely is bad, as it tends to mean that little things like life-support don't have power anymore.
Deus Siddis
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Re: Can radiator fins face each other?

Post by Deus Siddis »

All very useful information, thank you both. So the impression I am getting for strike and corvette craft is they rely mostly on often redundantly placed solid radiator fins and some solid radiators on the hull; the surface color of these solid radiators' material is black when cool.

Now for the next realism and canon question on this subject. Can radiator fins be curved surfaces or should they only be planar? How inefficient would this be for them to be nonplanar curvy surfaces?

I ask this primarily with the Rlaan vessels and installations in mind as they might benefit from such a look now that we have the polycounts to give it to them and it might also make more sense for them since their fins are also for 'shield manipulation'. (I guess these shields are composed of plasma that is manipulated magnetically?)
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Re: Can radiator fins face each other?

Post by chuck_starchaser »

What matters is the average profile of a radiator. If you took a camera with you and made thousands of snapshots of a radiator from all directions at equal distances, then measured the area it occupies in each pictured, and computed the average area, the radiation efficiency for a given radiator would be proportional to that, all other things being equal. Whether the surfaces are flat or curved shouldn't matter one iota. Perfect opportunity to define racial traits! It would be great if one day you could see a ship you've never encountered before and tell whether it's Rlaan, Aeran or whatever, just by the shape and material used for its rads. For example, some human groups, like purists would probably like mechanical things to look mechanical and distinct from the human form, might favor straight lines and sharp edges on their rads; like cylinders with four orthogonal, rectangular fins. Humans in general might use black anodize aluminium for rads. The Rlaan might prefer sail-like rads of some high dielectric material, as they use the rads for shield maintenance purposes. Aeran rads could look like an oval shape with like tear-drop appendages sticking out; not sure about aeran materials, in general. Just out of the top of my head. JackS?
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