Project ForgeMass Transfer
Diffusion
GATE 2020
Hard
Pure gas P is absorbed into a liquid; the dissolved P undergoes an irreversible first-order reaction in the liquid film. Which curve represents the steady-state concentration profile of P in the liquid film (interface at x=0)?
- Alinear decay from the interface to the bulk-liquid boundary
- steep exponential-like decay near the interface, flattening to ~zero well before the bulk boundary
- Cnearly flat near the interface, curving sharply downward just before the bulk boundary
- Dconstant in the film, then a step drop to bulk value
Explanation
For a fast first-order reaction consuming P as it diffuses into the film (large Hatta number), the concentration profile is C=Ci·exp(−x√(k/D)) — a steep exponential decay from the interfacial value that reaches essentially zero well within the film, unlike the linear (no-reaction) or cosh-shaped (finite-film, no-flux boundary) profiles.
Source: GATE CH 2020 (2020)
This question is part of a 15-day revision cycle — sign in and Project Forge will bring it back the day before you'd forget it.