Mass Transfer Operation Lecture series -Lec6B.pptx
1. 04-04-2024 Side 1
Madan Mohan Malaviya Univ. of Technology, Gorakhpur
Mass Transfer Operation-I
BCT-27
Dr. Prateek Khare
Assistant Professor
Department of Chemical
Madan Mohan Malviya University of
Technology Gorakhpur (UP State Govt. University)
Email: pkch@mmmut.ac.in
2. 04-04-2024 Side 2
Madan Mohan Malaviya Univ. of Technology, Gorakhpur
MASS TRANSFER COEFFICIENTS
Equimolar counter-diffusion of A and B (NA =-NB)
4. 04-04-2024 Side 4
Madan Mohan Malaviya Univ. of Technology, Gorakhpur
Example Hydrochloric acid (A) diffuses through a thin film
of water (B) 4.0 mm thick at 283 K. The concentration of HCl
at point 1 on one boundary of the film is 12 wt% and on the
other boundary, at point 2 is 4 wt%. The diffusivity of HCl in
water is 2.5 x 10-9 m2/s. Calculate the flux of HCl
considering water to be stagnant. Density of the solutions at
points 1 and 2 are 1060.7 kg/m3 and 1020.15 kg/m3
respectively.
5. 04-04-2024 Side 5
Madan Mohan Malaviya Univ. of Technology, Gorakhpur
At point 2, mole fraction of HCl
Average molecular weight at point 2
For z = 4 mm = 0.004 m,
Flux of HCl
6. 04-04-2024 Side 6
Madan Mohan Malaviya Univ. of Technology, Gorakhpur
Mass transfer under laminar flow condition
Mass transfer coefficient does not play a big role in
laminar flow condition as molecular diffusion exists
there. In laminar flow regime, the average liquid phase
mass transfer coefficient, kL,av is correlated with
Sherwood number (Sh) and DAB as follows
7. 04-04-2024 Side 7
Madan Mohan Malaviya Univ. of Technology, Gorakhpur
Mass transfer under turbulent flow past
solids
Mass transfer under flow past solid is a practically useful situation.
Several theories have attempted to clarify the behavior of mass
transfer coefficients.
All the theories have some assumptions and some drawbacks.
Hence, these are revised frequently.
In turbulent flow medium, small fluid an element of different
sizes, called eddies, move randomly. These eddies form, interact
among others and disappear in the flow path. The total molar flux of
a solute A due to molecular diffusion and eddy diffusion, JA is as
follows
