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Re: Black & White Question



>> In space, (no convection cooling) Here is the steady state equilibrim
>> temperature of a flat plate in the very hot sun.
>>
>>    WHITE     50 deg F
>>    BLACK     90 deg F
>>    ALUMINUM 788 deg F  (no typo)
>
>
> I remember a company that made DC generators built from themocouples 
> mounted
> to heat sinks. They blasted a propane torch on one side to generate 
> power.
> The idea was that there are no moving parts making the system very 
> reliable.
> I wonder what the efficiency/generating capacity is if solar cells VS
> themocouples. With these kind of temperature gradients thermocouple 
> power
> generation could be a pracitcal alternative to solar cells and they 
> probably
> would not dgrade as much over time.

The problems would be:
- getting a good thermal connection to the aluminum side without making 
an electrical connection
- finding a material for the cold side that would radiate and conduct 
heat well (black coated aluminum?)
- making the whole assembly mechanically solid enough to survive 
launch/deployment
- ensuring the hot side keeps its normal pointed close to the sun

The benefits might be numerous.  You could get pretty decent current out 
of a solar thermopile, and depending on how cold the cold end is 
(shading/insulation?) you could get pretty efficient power conversion.  
Maybe not as efficient as a photovoltaic panel, but it would definitely 
be an interesting experiment.

What I picture is a pair of flat pieces of aluminum,  one polished and 
facing the sun, one blackened and facing deep space, powered by the heat 
differential with a long string of hot/cold thermocouples in series to 
step up the voltage.  It would take quite some time to engineer and 
build, but would be worth trying at least ..

"Go ahead and do it, you can apologize later." -- RADM Grace Hopper, 
1906-1992
"The sunset is an illusion, but the beauty is real." -- Richard Bach
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