MASS TRANSFER AND SEPERATION Question Papers (Supple, 2005)

SET: 1

1. Obtain an expression for steady state equimolar counter diffusion of two gases starting from fundamentals?

2. On the basis of Colburn analogy, estimate the value of mass transfer coefficient for the absorption of ammonia by the wet surface of a cylinder placed in a turbulent air stream flowing across the cylinder at 4.6m/sec. heat transfer coefficient as 1.357 × 10-4 KJ.

DATA FOR AIR PRANDTL NUMBER = 0.74

CP = 0.49 × 10-3 KJ/Kg K

DENSITY (ρ) = 0.0012 Kg/m3 and for

Dilute ammonia – air mixture Schmidt number is 0.61

3. A liquid mixture containing 50 mol% n- Heptane and 50 mol% n – octane is subject to a differential distillation at atmospheric pressure untill the residual liquid contains 35 mole % n-heptane. Using the equilibrium data determine the percentage of feed that is left over as residue.

X 0.50 0.46 0.42 0.38 0.34 0.32

Y 0.689 0.648 0.608 0.567 0.523 0.49

Where X = mole fraction of n – heptane in liquid.

Y = mole fraction n – heptane in vapour.

4. A continuous fractionating column operating at atmospheric pressure is to separate a feed mixture containing 30% CS2 & 70% CCL4 into an over head product of 95% CS2 and a bottom product of 95 mole% CCL4 . The feed enters as a liquid at its boiling. Assume an over all efficiency of 70% and a reflux ratio of 3:1. Estimate the number of plates needed. All the compositions are in mole %.

Equilibrium data

X 0.0296 0.0615 0.258 0.39 0.532 0.663 0.758 0.860

Y 0.0823 0.1555 0.494 0.634 0.747 0.830 0.880 0.932

5. With the help of neat sketches, explain briefly the various types of commercial extraction equipment.

6. Give an account of the graphical method of calculation of the number of stages for counter current extraction in a solid-liquid extraction system.

7. Write on:

a) Adsorption wave and break through curve

b) Pressure solving and thermal solving methods. BET isotherm.
Write a brief note on counter current flow model for gas permeation.