function of ln(Pe) in Figure 5-6B. A linear relation is found between the amplification and the
logarithm of Peclet number of flow. As the Peclet number increases, the ridged channel
becomes less effective in fluid mixing. This can be explained by that a flow with a larger Peclet
number becomes more dominated by the streamwise convection, and the mixing effect from flow
twisting becomes negligible.
5.2.4 Flow Recirculation Intensity
To induce flow recirculation, pressure and electric field are simultaneously imposed on the
ridged channel model. In the simulation, the pressure gradient is applied by fixing the pressure
at inlet zero and imposing a finite pressure, P, at the outlet, so that the pressure flow is from right
to left in the top view, as illustrated in Figure 5-7a. The electric field is imposed by setting a
finite electric potential, V, on the inlet of ridged channel model, while keeping the outlet
grounded all the time. The resulting EOF in the channel is from left to right in the top view of
the flow (Figure 5-7b). In the simulation, the electroosmotic mobility is set as 4.8x10-8 m2/s.
CFD-VIEW is used to analyze the flow field and visualize the calculated streaklines in the
flow. Particle streaks were calculated from the simulated flow field. A total of 141 streaklines
are generated in the flow, each of which represents the trajectory of a massless particle travels
with the flow. The particles are released from an array of locations near the ridge structure
(Figure 5-4c). The streaklines are calculated by connecting 500 segments of 1-millisecond travel
distance.
Figure 5-7 shows the simulated trajectories and flow velocity profiles in a Poiseuille flow
and an electroosmotic flow in the ridged channel. Quadratic velocity profile is identified in the
pressure driven flow, so are the front of the streaklines. In the EOF, the velocity profile has a
much more uniform profile, so that all the particles travel about equal distance with the same
time lapse. No flow recirculation is observed in both flows. Similar to what we predicted in a