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Mass Transfer
Diffusion
GATE 2009
Medium

Species A is diffusing at steady state from the surface of a sphere (radius=1cm) into a stagnant fluid. If the diffusive flux at a distance r=3cm from the center of the sphere is 27 mol/cm².s, the diffusive flux (in mol/cm².s) at a distance r=9cm is

  • A1
  • 3
  • C9
  • D27

Explanation

At steady state, total molar flow N(r)×4πr²=constant, so flux N(r)∝1/r². N(9)=N(3)×(3/9)²=27×(1/9)=3.

Source: GATE CH 2009 (2009)

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