| Summary: | The effect of unsteady thermocapillary convection on the mass transfer rate of a
solute between two immiscible liquids within a rectangular microscale channel with
differentially heated sidewalls was numerically investigated. A computational fluid
dynamic code in Fortran77 was developed using the finite volume method with Marker
and Cell (MAC) technique to solve the governing equations. The discrete surface
tracking technique was used to capture the location of the moving liquid-liquid interface.
The code produced results consistent with those reported in published literature.
The effect of the temperature gradients, the aspect ratio, the viscosity of liquid,
and the deformation of the interface on the mass transfer rate of a solute were studied.
The mass transfer rate increases with increasing temperature gradient. The improvement
of the mass transfer rate by the thermocapillary convection was found to be a function of
the Peclet number (Pe). At small Pe, the improvement of the mass transfer rate increases
with increasing Pe. At high Pe, increasing the Pe has no significant effect on increasing
the mass transfer rate. Increasing the aspect ratio of the cavity up to 1 increases the mass
transfer rate. When the aspect ratio is higher than 1, the vortex moves only near the
interface, resulting in decreasing the mass transfer rate. By increasing the viscosity of the
liquid in top phase, the maximum tangential velocity at the interface decreases. As a
result, the improvement of the mass transfer rate decreases. The deformation of the
interface has no significant effect on the improvement of the mass transfer rate.
By placing the heating source at the middle of the cavity, two steady vortices can
be induced in a cavity. As a result, the mass transfer rate is slightly enhanced than that in
the system with one vortex. By reversing the direction of the temperature gradient, the
mass transfer rate decreases due to the decrease in the velocity of bulk fluid. The
thermocapillary convection also promotes the overall reaction process when the top wall
of the cavity is served as a catalyst. === Graduation date: 2005
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