[Prev][Next][Index][Thread]

Dirigible floor lamp musings



If the balloon weighs 1 pound per 400 ft^2 (What do dry cleaner bags weigh?),
with an R-value of 0.6 ft^2-F/Btu, and the inside air temperature is 175 F
(will that melt the bag?), and the room air is 68 F, how big must it be to
support itself?

Sea level air at 175 F weighs 0.0625 lbs/ft^3, so 68 F air should weigh
about 0.0752 lb/ft^3, ignoring humidity. The lifting force should be
at least 0.0752 - 0.0625 = 0.0127 lbs/ft^3. 

An r' radius sphere would be self-supporting when 

4 pi r^2/400 = 4/3 pi r^3 x 0.0127 ==> r = 3/(400 x 0.0127) = 1'.

Keeping the air hot requires 

(175F-68F) x 4 pi 1^2 ft^2/R0.6 = 2241 Btu/hour or 657 watts.

Too much, except for a sometime toy...

Where can I buy some very fine tungsten wire?

Nick