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re: lift a weight (5kg) with the energy from a candel
31 jul 1998
eur van andel wrote:
>>let's say we don't use levers, and the balloon material weighs 10 grams
>>per square meter, and it has a thermal conductance of 5 w/m^2c, and the
>>candle makes 50 watts and weighs 500 grams, and the 20 c air in the room
>>weighs 1.2 kg per cubic meter...
>let's take round balloon, radius r, air temp in balloon t.
>
>surface of balloon 4 pi r^2
>contents of balloon 4/3 pi r^3
>weight of balloon 9.81*0.04 pi r^2
why 9.81, i wonder...
>power to heat balloon 4 pi r^2 *5 * (t-20)
i think the idea was to use only one candle... just 50 watts.
>so, to lift 5 kg:
>
>9.81*(5+0.04 pi r^2)=4/3 pi r^3 (1.2-ro_t)
or maybe just
5+0.5+0.04 pi r^2 = 4/3 pi r^3 (1.2-ro_t),
including the weight of the candle.
>oops. excel to the rescue... so: a 7.16 m diameter balloon, with 16 candles.
with only 1 candle, it seems to me the answer is "it can't be done." the
optimum balloon diameter is about 6.6 m, with a lift/weight of about 0.2.
now how about those solar versions?
nick
hint: bill sturm @ specialty cea structures inc. in calgary alberta canada
(403) 274-8800 now has a 12,000 sf greenhouse that uses soap bubbles as the
insulation/shading method, and they are building a 120,000 sf greenhouse...
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