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re: dirigible wind turbines
2 dec 1997
jerry chase writes:
>why not a hot air balloon? >
it has to be a lot bigger, especially if it stays up at night, and the wind
blows at night too... 30 f air weighs about 0.081 lb/ft^3, r1 uv poly film
weighs about 0.03 lb/ft^2, the balloon might collect 1000 btu/ft^2/day of
south-facing surface in december, and we want to support about 65 pounds net.
a balloon with radius r would collect about 0.9x1000xpir^2 of sun and lose
about 24hx(t-30f)x4pir^2/r1 in december, making the interior temperature
t=39 f, for a bouyancy force of (1-(30+460)/(39+460))0.081 = 0.0015 lb/ft^3,
so 0.0015(4/3pir^3)=0.03(4pir^2)+65, or r^3= 60r^2+310, making r about 60',
ie a 120' vs 10' diameter balloon. it might stay up during a cloudy week
if we somehow added enough warm thermal mass, eg water, to keep the minimum
interior temperature above that required for bouyancy, but this approach
already seems impractical for anything smaller than a floating city.
>better to tether something small to three or more balloons...
that wouldn't necessarily speed up the wind past the turbines by
compressing the airflow or rotating the structure into the wind.
nick
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