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1.5.2.2.4, Model ofKishinevski
Kishinevski accepts [27 5 39] that the mass transfer is carried out mainly
by turbulent diffusion assuming that the coefficient of the turbulent diffusion D t
is independent of the distance from the interface.

1.5.2.2.5. Model of diffusion boundary layer
This model is developed in the works of Frank-Kamenetzki [21],
Levich [22], Sherwood [23], Ruekenstein [24] and others and is based on the
simultaneous consideration of the equations of hydrodynamics and convective
diffusion in moving medium. Because of very small thickness of the diffusion
film, it is enough to take into account only the diffusion in direction to the
interface. Thus, the equation of the convective diffusion of the liquid phase can
be written as follows.

2
8C n8 C L dC L f,^
= D—r--w—- (162)
8z 3 By
8d t
where w is velocity.
The boundary condition at the interface is:

(163)

At steady state conditions from Eq.(79)it follows:

^ = w^ , (164)

From the solution of the equation given above it follows that far from
the interface Ci=const. and near to it the concentration sharply changes. The
mass is transferred in the layer by molecular and convective diffusion. The
turbulent diffusion is absent at these conditions. The solving of the equations
shows also that the thickness of the boundary layer increases with increasing of
its length. That is why the increasing of the length of the interface leads to
reduction of the mass transfer rate.