Convective mass transfer of A in

1
Convective mass transfer of A in stagnant B
General equation for convective mass transfer
Direction of bulk convection
For no flux of B in the z direction, i.e. when B
is stagnant along the z axis
Stationary
Therefore
y
z
Where
2
Mass transfer coefficients of A in stagnant B
In gaseous medium
In liquid medium
3
Experimental determination of mass transfer
coefficient

• Mass transfer coefficient involves molecular
  diffusivity, eddy diffusivity and distance over
  which mass transfer is taking place
• Eddy diffusivity is difficult to determine
• Mass transfer coefficient can be determined
  experimentally
• Experimental measurement is based on mass of
  solute transferred over a period of time

Flux Mass transfer coefficient ? Concentration
difference Mass of solute transferred Flux
---------------------------------------
Time ? Area Mass of solute
transferred Mass transfer coefficient
--------------------------------------------------
--- Time ? Area ? Concentration
difference
4
Dimensionless correlations for mass transfer
coefficient

• Based on heat-mass transfer analogy
• Correlations are based on three or more
  dimensionless groups
• The three dimensionless groups that are always
  present in these correlations are the Reynolds
  number (NRe), Sherwood number (NSh) and Schmidt
  number (NSc)