$3\mathrm{.}4$ Winding and Cheney $[$Ind$.$ Eng. Chem., $40,1087(1948)]$ passed air through a bank of rods of

naphthalene. The rods were of "streamline" cross section, arranged in staggered array, with the air

flowing at right angles to the axes of the rods. The mass$-$transfer coefficient was determined by

measuring the rate of sublimation of the naphthalene. For a particular shape, size, and spacing of the

rods, with air at $37\mathrm{.}8C(100F),1$ std atm, the data could be correlated byt

$k_G=3\mathrm{.}58{10}^{-9}{G}^{0\mathrm{.}56}$

where $G^{\text{'}}$ is the superficial mass velocity, $k\frac{g}{m^2}*s,$ and $k_G$ the mass$-$transfer coefficient, kmo$\frac{l}{m^2}.$

$s*(\frac{N}{m^2}).$ Estimate the mass$-$transfer coefficient to be expected for evaporation of water into

hydrogen gas for the same geometrical arrangement when the hydrogen flows at a superficial

velocity of $15\mathrm{.}25\frac{m}{s}(50f\frac{t}{s}),37\mathrm{.}8C(100F),2std$ atm pressure. $D$ for naphthalene$-$air, $1$stdatm,

$37\mathrm{.}8C=7\mathrm{.}03{10}^{-6}\frac{m^2}{s}$; for water$-$hydrogen, $0C,1$stdatm,$7\mathrm{.}5{10}^{-5}\frac{m^2}{s}.$