How does radiator generate power ?

[Lohan2008]

Can someone give me a basic explanation of how does a radiator generate power when it is in space ??

[Bill Phil]

Do radiators generate power? Thought they only got rid of waste heat.

Do you mean RTGs? They use the decay of radioactive material to heat up a substance and use a pressure fed device to spin up a generator. Unless that's not how they work...

[Dodgey]

No that isn't how an RTG works, basically they use a lump of plutonium to generate heat and use thermocouples to transform the thermal gradient between the plutonium and radiators into electricity.

[Camacha]

Do you mean RTGs? They use the decay of radioactive material to heat up a substance and use a pressure fed device to spin up a generator. Unless that's not how they work...

This is true of Earth bound fission reactors, but not for RTGs.

[SargeRho]

No, that is true of RTGs, not of Earth-bound fission reactors. You're mixing things up.

[Camacha]

No, that is true of RTGs, not of Earth-bound fission reactors. You're mixing things up.

Unless I am misunderstanding you, it is exactly the other way around. Earth bound fission reactors generally uses steam to drive a turbine (the aforementioned pressure fed device), in turn powering a generator which produces electricity.

While an RTG produces power directly from heat using thermocouples using the Seebeck effect. No steam or similar interface medium is involved. Interestingly, the same effect in reverse is used to cool computers for extreme overclocking, though that is generally named afters its discoverer Peltier.

Edited January 31, 2015 by Camacha

[Tommygun]

Can someone give me a basic explanation of how does a radiator generate power when it is in space ??

Thermocouples in the RTG use what's called a Seebeck effect (right side in picture).

Basically when you apply heat to two dissimilar materials(Pink and Green Blocks in Picture) it causes electrons/current (eletricity) to flow.

Edited January 31, 2015 by Tommygun

[SargeRho]

I was replying to Bill Phil...I got ninja'd by both you Camacha, and Dodgey.

[Camacha]

I was replying to Bill Phil...I got ninja'd by both you Camacha, and Dodgey.

Quoting saves lives!

[RainDreamer]

Hmm...can't we salvage the waste heat and use it to generate power? in that way the radiator may kinda generate power somehow. Though it may be very ineffective that way and may hinder waste heat disposal...

[KerikBalm]

from an RTG? yes, you could, but the equipment would be really heavy. On Earth, you'd use the heat to drive a steam turbine, and get decent efficiency. In space, a termocouple is much lighter - but its efficiency is rather low (10-20% IIRC). It takes less mass to just bring more plutonium and thermocouples, than to try and recover usefull energy from the waste heat.

All this is assuming that the OP is even talking about RTGs.... it says the OP is from an English speaking country... so I would have hoped for a bit more eloquence...

[lajoswinkler]

Hmm...can't we salvage the waste heat and use it to generate power? in that way the radiator may kinda generate power somehow. Though it may be very ineffective that way and may hinder waste heat disposal...

It would lower the efficiency of the primary power generator. Work is done by heat gradient, not by heat.

As you can see here, the hotter the source and the colder the sink, the more work you get.

[Tommygun]

I just remembered about the Stirling RTG, that does cycle helium gas through it.

http://en.wikipedia.org/wiki/Stirling_radioisotope_generator

http://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope_generator

[Camacha]

I just remembered about the Stirling RTG, that does cycle helium gas through it.

http://en.wikipedia.org/wiki/Stirling_radioisotope_generator

http://en.wikipedia.org/wiki/Advanced_Stirling_radioisotope_generator

Did either of them actually fly? I cannot seem to find any missions that used them, though plenty of proposals have been made. If any did, it seems it must have been in the past 5 years.

[Tommygun]

No, none have flown yet.

[kahlzun]

The other thing to keep in mind is that thermocouples generate heat as part of their process.

You can't just run waste heat through it and turn it into power, you get some free power, and some more heat to radiate away. Useful if you need to keep something warm, less so in space.

[Nuke]

thats the dynamics part of thermodynamics, you have to move the heat before you can use it to generate power. in this case from the heat source, a reactor for example, and a heat sink, the radiator, usually going through a turbine to generate power. rtgs also do this. heat is moved through thermocouples on its way to the radiator fins, generating electricity in the process (in a horribly inefficient manner). in both types of system heat is moving and there is a means for generating electricity somewhere in the middle of the system.

Edited January 31, 2015 by Nuke

[architeuthis]

Hmm...can't we salvage the waste heat and use it to generate power? in that way the radiator may kinda generate power somehow. Though it may be very ineffective that way and may hinder waste heat disposal...

Not for generating power, except though topping cycles, but you're still ultimately stuck at something below the Carnot limit efficiency. This is due to the 2nd law of thermodynamics, and there is no way around it unfortunately (except by generation through an infinite temperature gradient, good luck with that). One thing you can do with low grade heat rejected from power generation is to use it as process heat (for instance the 1950's idea of using waste heat from municipal atomic piles for central heating on a citywide scale). This basic idea is called co-generation.

Edited January 31, 2015 by architeuthis

[sgt_flyer]

Nasa do use the waste heat of it's RTGs to help for the heating of it's probes / rovers. (probes RCS bi or monopropellant tanks needs to be heated at the correct temperature before they fire the thrusters - and some instruments also have specific operating temperatures. - when they have RTGs on board, they can use the waste heat instead of having to use electricity to do equivalent heating.