Aviation Forums

Andrew Nowicki · Guest

A foam made of soap bubbles seems to be well suited
for thermal insulation of hot air balloons and
dirigibles. Soap bubbles burst when they dry up. When
they are held inside a sealed container, they do not
dry up, so they do not burst, but gradually shrink
in size until they disappear. Eiffel Plasterer made
a soap bubble which lasted 342 days!

My favorite design of the insulated balloon has the
envelope made of two layers of Teonex. Soap bubbles
are held between the two layers. The inner layer
holds steam or hydrogen which provides buoyancy.

Solar powered, insulated dirigibles may someday
replace most of the military aircraft. Energy
collected by the solar cells can be converted to
hydrogen, stored as hydrogen gas inside the dirigibles,
and used up at night. Compared with the conventional
aircraft, the dirigibles are quiet, and have unlimited
range and endurance. These advantages make them useful
in the war against terrorists.

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RELATED LINKS:

Canadian greenhouse insulated with soap bubbles:
http://www.tdc.ca/bubblegreenhouse.htm

Steam balloons:
http://www.flyingkettle.com/jbfa.htm

Soap bubble recipes:
http://www.exploratorium.edu/ronh/bubbles/formulae.html

Solar powered airplanes:
http://www.skytowerglobal.com/begin.html

My email address is at:
http://www.islandone.org/LEOBiblio/ANOWICKI.HTM

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CALCULATIONS

If the balloon is not insulated, the heat loss Hr is
dominated by thermal radiation:
Hr = 5.7x10^-8xExAx(T1^4 - T2^4), where:

E = emissivity = about 0.5 (wild guess)
A = surface area of the balloon
T1 = absolute temperature of the balloon = 373 K
T2 = absolute temperature of the ambient air 273 K
D = balloon diameter = 10 meters
(All units are metric.)

A = 3.14xd^2 = 314 m^2

Hr = 123,517 W

Do soap bubbles absorb thermal radiation?
Wavelength of the maximum intensity of the
thermal radiation is given by the Wien's Law:
Lambda = 0.0029/T1 = about 8 micrometers.

If the thickness of the soap bubbles is 1/4
of the wavelength (2 micrometers), complete
destructive interference will result, so the
bubbles will suppress heat loss due to
thermal radiation.

Heat loss by convection is smaller: Hc = CxAxT, where:

C = convection coefficient = approx. 1.3x(T/D)^0.25
A = surface area of the balloon
T = temperature difference = 100 deg
D = balloon diameter

C = 2.3, A = 3.14xd^2 = 314 m^2, Hc = 72,626 W

The heat loss by convection is much greater when
the balloon moves relative to ambient air.

Thermal conductivity of the soap bubbles is
certainly smaller than that of Styrofoam because
the soap bubbles are very thin; on the order of one
micrometer. If the balloon is insulated with one
meter thick layer of Styrofoam, the heat loss is:
Hd = KxAxT/L, where:

K = thermal conductivity of styrofoam = 0.01,
A = surface area of the balloon = 314 m^2
T = temperature difference = 100 deg
L = thickness of the Styrofoam insulation = 1 m

Hd = 314 W