/sci/ - Science & Math » Thread #12235465

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Anonymous Thu 15 Oct 18:42:55 2020 No.12235465 View Reply Original Report

Quoted By: >>12236590 >>12236681 >>12236691 >>12236782 >>12236804 >>12238422 >>12238653

In art, "realistic" future spaceship always has exposed glowing hot radiators.

Wouldn't be smarter to instead of having those exposed radiators radiating precious black body radiation away, cover them up with thermophotovoltaics in order to recover at least some of it?

How much could you even recover that way? IIRC TPV has theoretical 80% efficency, but obviously it would depend on specifics.

What are your thoughts.

Anonymous

Anonymous Fri 16 Oct 2020 00:07:51 No.12236590 Report

Quoted By:

>>12235465
>>cover them up with thermophotovoltaics in order to recover at least some of it
generally speaking no, because that slows down heat transfer.

Anonymous

Anonymous Fri 16 Oct 2020 00:41:47 No.12236681 Report

Quoted By:

>>12235465
>In art
In reality solar panels often absolve the function of radiators. In case a radiator is needed it's usually just a metal panel painted black or white, depending on the mission, and its temperature must be always lower than the maximum allowable temperature of the component it has to cool (usually electronics, or the hot side of the cooling systems of some sensor that has to work at near-zero kelvin).
>thermophotovoltaics
Never heard of it, so I assume it's not a go-to technology for aerospace. Wikipedia says it works for very high temperatures which is something that spacecrafts tend to dislike.
>theoretical 80% efficiency
Wikipedia quotes that number, but that's just the upper limit imposed by thermodynamics: anything photovoltaic is in the ballpark of 20%.
>What are your thoughts.
If you have a thermal differential you want to use to make electrity there's always thermoelectric conversion, but Seebeck effect produces really infinitesimal voltages so TEG have an abysmal efficiency, something like 5%, but they're reliable as hell and that's what matters so they're used in RTG (nuclear batteries).
Assuming a spacecraft has a heat source capable of making radiators glow while in space, I'd say you can slap a proper steam cycle (they're on the heavier side of things, and more complex, but if you have all that power available then they're worth it because you can make them crazy efficient).

t. Aerospace Engineer

Anonymous

Anonymous Fri 16 Oct 2020 00:47:01 No.12236691 Report

Quoted By:

>>12235465
>Wouldn't be smarter to instead of having those exposed radiators radiating precious black body radiation away, cover them up with thermophotovoltaics in order to recover at least some of it?
No, because such systems work on a heat gradient and not heat itself. Radiators would still be needed.

Anonymous

Anonymous Fri 16 Oct 2020 01:20:47 No.12236782 Report

Quoted By: >>12238429

>>12235465
>Wouldn't be smarter to instead of having those exposed radiators radiating precious black body radiation away
It's not precious, it's a dangerous waste product which is why it's being radiated away.

>cover them up with thermophotovoltaics in order to recover at least some of it?
1) total meme, if you wanted to use the waste heat you would just use the heat in a stirling engine or something
2) something like this would already be used like using waste heat to heat rooms etc.

Obviously you could try to build a design that has to radiate less away but that comes at the cost of other mission parameters. putting up a shell of thermophotovoltaics around your radiator and installing radiators to those will mean lot of added mass for not a lot of gain meaning you either go slower or some other sacrifice.
In fact even if you had 80% efficiency you are producing electricity that will convert to heat at a 100% efficiency meaning you still have to dump the original amount of energy into space to prevent the ship from heating up. The real tradeoff with radiators is using a small radiator that runs hot or a large radiator that runs cold. You need high thrust to weight ratio to do anything in space and that basically means having glowing radiators to have a stronger engine on a smaller ship.

Anonymous

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Anonymous Fri 16 Oct 2020 01:28:08 No.12236804 Report

Quoted By:

>>12235465

Anonymous

Anonymous Fri 16 Oct 2020 13:44:15 No.12238414 Report

Quoted By: >>12238489

My general point was that you would shift some of the cost and weight from powerplant to "recycling" and end up with same or even greater amount of electricity. I get that you would still have to dump some of the heat.

Anonymous

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Anonymous Fri 16 Oct 2020 13:47:12 No.12238422 Report

Quoted By: >>12238508

>>12235465
>In art, "realistic" future spaceship always has exposed glowing hot radiators.
no they don't

Anonymous

Anonymous Fri 16 Oct 2020 13:51:57 No.12238429 Report

Quoted By: >>12239240

>>12236782
Personally would love to see some space applications of stirling engines

Anonymous

Anonymous Fri 16 Oct 2020 14:17:09 No.12238489 Report

Quoted By: >>12238639 >>12238680

>>12238414
I suggest you pick up a thermodynamics textbook

Anonymous

Anonymous Fri 16 Oct 2020 14:20:46 No.12238508 Report

Quoted By:

>>12238422
What's realistic about that? It looks like some sort of service vehicle but it has no cargo space and is shaped stupidly.

Anonymous

Anonymous Fri 16 Oct 2020 14:58:20 No.12238639 Report

Quoted By:

>>12238489
Photovoltaics working of black body radiation are physics breaking? How interesting.

Anonymous

Anonymous Fri 16 Oct 2020 15:03:15 No.12238653 Report

Quoted By:

>>12235465
Why would you have a radiator in the first place if you don't WANT to get rid of the energy?

Anonymous

Anonymous Fri 16 Oct 2020 15:14:00 No.12238680 Report

Quoted By: >>12239271

>>12238489
thermodynamics has been debunked a long time ago man

Anonymous

Anonymous Fri 16 Oct 2020 16:52:12 No.12238972 Report

Quoted By:

If you hear someone say something like "recycle waste heat", just turn away and leave them be.

Anonymous

Anonymous Fri 16 Oct 2020 18:15:21 No.12239240 Report

Quoted By:

>>12238429
NASA worked and is working on something of the sort.

Anonymous

Anonymous Fri 16 Oct 2020 18:28:39 No.12239271 Report

Quoted By:

>>12238680
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