Abstract:
Micro-electrodes with exposed areas ranging from 5-30 mm2 were placed onto 4.5 mm alumina
spheres and used for the sub-particle scale quantification of liquid-solid mass transfer. A novel
electrochemical technique was applied where the external cathode wetting fraction and liquid-solid
mass transfer were simultaneously quantified. Clear bifurcation of the area-specific liquid-solid mass
transfer was observed, providing direct evidence of the two-wetted-zone theory previously inferred
from tracer response analysis. The lower hysteresis branch (Levec prewetting) exhibited larger
fractions of static wetted area compared to the upper branch (Kan prewetting). The static zones
were not completely stagnant and the average static mass transfer rate increased with liquid
superficial velocity. The spatial position of the static zones varied for a given packing configuration,
while no relationship was found between the positioning of static and residual holdup. Static liquidsolid
mass transfer coefficients were found to be higher than those obtained from tracer response
analyses on porous particles.
