ABSTRACT
Determining mass transfer film coefficients is the major
application of the Sherwood number. According to the
principle of dynamic similarity, regardless of the indivi-
dual values of specific system properties, relationships
between dimensionless numbers are the same, and this is
most useful for scale-up. The resistance to convective mass
transfer across the boundary layer is related to the film
coefficient K. Everything that affects the flow properties
and streamlines of the fluid around the interface will affect
the thickness of the boundary layer and hence the value of
K: this includes not only the physical properties of the fluid
(e.g., density, viscosity), but also size, shape, and smooth-
ness of the surface. Furthermore, the thickness of the
boundary layer is rarely constant along the whole interface.
Therefore, K can only be determined in situ, or then esti-
mated from dimensionless correlations.
