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I'm in the midst of writing a space opera, and there are several characters that are sentient androids and I need some help with their physiology. I have them set up with small fusion cores for power, quantum computing brains, and nanite self repair. They obviously have no need to breathe and only have lungs in order to speak.
Would they need the equivalent of blood? What would their synthetic flesh be composed of? How would they "refuel"?
Why do you need blood?
In living beings blood is used to
Now, for 1. you don't need blood. Some simple wiring can convey the energy where is needed.
For 2., since you have a centralized energy production, you can use the equivalent of lungs to create a "breathe assisted" cooling, where the primary coolant is a liquid which then exchange heat with air in the lungs via breathing. This however will be less efficient than a continuous flow, since your android would have to inspire and expire. A similar system can be used to maintain thermal balance in joints when needed.
To feed the fusion core you can simply have the android drink, once in a while, some heavy water integrated with lithium salts.
Flesh will be replaced by the systems used to actuate movements, something like nano-machines a la MEMS.
Supposed you really wanted them to have something resemling blood (because it's really a lot more hipster than just cables), your nanite self repair system might be the reason for that.
The system of blood vessels in biological creatures is extremely complex from a geometrical point of view, but since you already have nanomachinery, and the underlying rules of this complexity are comparably simple, you should not have a problem there.
Now to the why-question:
nanomachines need power in order to operate. If you imagined some kind of reservoir, or garage, for your nanites, where they are parked and recharged when they are not repairing anything, you need a means for them to reach the place in the body where they are needed.
Obvoiously they could use their internal means of propulsion, e.g. crawling, to reach their target destination, but that would drain their batteries. If instead you had a system of tubes similar to a creature's blood vessels, you could float them to their target location, pushed by a central pump.
It is even possible that a breach in the system (a damage comparable to an open wound) even facilitates the process: the pressure in the system already pushes the nanites to the opening.
The same system can be used to remove waste, like bits of things that were remoed by the nanites, back to a central storage.
The fact that a blood-like system allows for quite some story twists is a plus, of course.
Oh, and you don't really need lungs to speak. a simple loudspeaker could do the job just fine. But, Admittedly, lungs are cooler.
You can use oil or lubricant as equivalent of blood. As the vessel, tubes. This will suffice if you only need a visualization of bleeding and death of blood loss (although that will be quite different).
However, if you need blood in the sense of a method of transportation system, then that will depend on what needs to be transported and why. For reference, you might want to consider water-based and oil-based solution.
For example, you might use a supercoolant liquid for a heatsink system for your quantum brain, because just water will not suffice.
As for refueling (the liquid), you can have the classic "gas tank". Or directly to the tubes.
This question is kinda broad, but I'll weigh in and answer all three questions.
On one end of the scale there's androids that are entirely flesh and blood like we are but were created through genetic engineering. Then you might have something that's mostly flesh'n'blood but has an implanted computer rather than a brain. An android made of a combination of biomass and electronics could be a best of both worlds solution, or it could be entirely synthetic but designed to be analogous to biology like the white-blooded androids in the Alien series. On the other end of the scale is the more traditional robot made of motors, electronics and covered in shiny plating, or maybe biomaterials made to imitate that appearance, shiny keratin over circuitry made of nerve fibres.
Anyway the most practical power source would either be some fuel burning engine/alternator setup (probably burning hydrogen so the only waste it produces is water) or using advanced batteries (lithium oxygen) or there's some wireless power supply and the android just has an on-board capacitor bank.
A traditionally designed robot could justifiably have various lubricants, coolants and liquid fuels that would leak out like blood if it was damaged; some kind of non-conductive fire-suppression foam would be a good idea too.
small fusion cores for power so no fuel reserves needed, unless they are producing enormous energy blasts.
quantum computing brains sounds small; good.
nanite self repair super nifty.
All you need now is to be able to move. The lighter you are the easier it is to move.
I propose your androids exist within an inflatable humanoid form.
Inflatable is cheap and flexible. Movement would be accomplished via pneumatics; tiny fans (powered by the fusion core) would push air into or pull air out of appendages, inflating or deflating regions corresponding to the muscle groups.
These light inflatable humanoids would easily be able to fly using their fans; an added bonus. Or they could bounce along as they walked, like people on the moon. Of course they could also walk at a stately pace like any humanoid, with the help of ballasted shoes. The nanites could easily scuttle out with tape to put on any holes.
An android could upload wirelessly into any such inflatable body as might be necessary (humanoid or otherwise). In circumstances where many balloon bodies might be used up in short order (e.g. an infantry battle) you might opt for batteries rather than the expensive fusion core. If acting only locally the quantum brain would be lost with the body and so would make sense for that to be remote, with the body providing a host computer from which to actuate the inflatable muscles.
A google image search for "inflatable doll" provides many, many images and much food for thought.
You need to decide how the power is transferred from the fusion core to moving parts - the core just produces heat and too many readers already understand this just to pass it. You can turn that to either to electricity, run some chemical reaction or mechanical force. Electricity you can get from the heat difference directly.
It's probably better to not try to explain it in too much detail, as you're just making stuff up and it has knock on effects on other parts of the built world - if you have a visual image in your head about how some scene should work, you can make up the details for that(Aliens style).
You're not probably going to into detail about exactly how the nanites work either, just that they work and for some reason don't replicate and they do not work outside of the body of the host android(I'm assuming this, since that would probably affect your story if they did in a big way) - so just have them be tied to the "blood" of the android like cells, if you don't you'll be soon facing the logical inclusion of T1000 like androids compromised entirely of nanites apart from the quantum brain device.
You need cooling of some sort as well and liquids are good at transferring heat from one place to another.
