A recent attempt to circumnavigate the world in a balloon used a helium-filled balloon whose volume was 7240 m3 and surface area was 1800 m2. The skin of this balloon is 2 mm thick and is made of a material whose helium diffusion coefficient is 1 × 10?9 m2/s. The molar concentration of the helium at the inner surface of the balloon skin is 0.2 kmol/m3 and the molar concentration at the outer surface is extremely small. The rate at which helium is lost from this balloon is
(a) 0.26 kg/h
(b) 1.5 kg/h
(c) 2.6 kg/h
(d) 3.8 kg/h
(e) 5.2 kg/h
(c) 2.6 kg/h
Ci=0.2 [kmol/m^3]
Co=0 [kmol/m^3]
D=1E-9 [m^2/s]
L=0.002 [m]
M=4 [kg/kmol]
A=1800 [m^2]
Ndot=D*A*(Ci-Co)/L
Mdot=Ndot*M*3600
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