ENGR263 2021 Q A2(c) (ENGR5002)

ENGR263 2021 Q A2(c)Past paperOld spec ENGR2632:212 marks14 min

ENGR263 Process of Mass Transfer Summer 2021 (open book) Q A2[PARTIAL] official answers Left out: (a) distillation vs evaporation (2 marks) and (b) precipitating dextran (2 marks) are separation-process questions that are not on the current syllabus.

Answer All parts (a) - (c). [Parts (a) and (b), 4 marks on distillation/evaporation and precipitation, are omitted.]

Oxygen is diffusing through a stagnant layer of methane 10 mm thick. The temperature is $20^\circ\mathrm{C}$ and the pressure $100\ \mathrm{kN/m^2}$ . The concentrations of oxygen on the two sides of the film are 15% and 5% by volume. The diffusivity of oxygen in methane at $20^\circ\mathrm{C}$ and $100\ \mathrm{kN/m^2}$ is $2.046 \times 10^{-5}\ \mathrm{m^2/s}$ .

Formulas you may need

Diffusion through a stagnant gas: $N_A = \dfrac{PD_{AB}}{RT\delta}\ln\dfrac{1 - y_{A2}}{1 - y_{A1}}$ (on the formula sheet)
Pressure correction: $D_{AB} \propto 1/P$ at fixed $T$ (on the formula sheet)
$R = 8314\ \mathrm{J\,kmol^{-1}\,K^{-1}}$ (learn this)

(c(i))
Calculate the rate of diffusion of oxygen in $\mathrm{kmol/(m^2\,s)}$ .
N_A =kmol m^-2 s^-1
[5]
(c(ii))
What will be the rate of diffusion if the total pressure is raised to $200\ \mathrm{kN/m^2}$ , other conditions remaining the same?
N_A =kmol m^-2 s^-1
[7]