Project ForgeMass Transfer
Diffusion
GATE 2015
Medium
A 2mm-diameter naphthalene sphere sublimes slowly in stagnant air at 25°C (diffusivity 1.1×10⁻⁶ m²/s, size change neglected). The mass transfer coefficient is B×10⁻³ m/s. B, rounded to 1 decimal place, is
1.1(± 0.1 accepted)
Explanation
For a sphere in an infinite stagnant medium, Sh=kc·d/D=2. kc=2D/d=2×1.1×10⁻⁶/2×10⁻³=1.1×10⁻³ m/s, so B=1.1.
Source: GATE CH 2015 (2015)
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