flow in a 2D wavy channel, the creeping electroosmotic/Poiseuille flow in a slow varying
channel doesn't have any backflows, hence no flow recirculation occurs. However in case both
pressure and electric filed are imposed simultaneously on the fluid in the ridged channel, flow
recirculation takes place around the ridge structures.
The flow recirculation is expected to be related to the ratio of electrokinetic force and the
pressure force in the flow. Inherited from the study of recirculation in 2D wavy channel, the
dimensionless parameter K = PL2/(4;rpvTo) (Equation 4-32), represents the ratio of
imposed pressure drop to electric potential difference on the fluid in the ridged channel. K is
zero when zero pressure drop is applied, and the electroosmotic flow prevails; K becomes
infinity in case that zero electric field is imposed on the fluid flow, hence the pressure flow
dominates. With the combination of different P and V, a total of 18 flows of different K are
simulated, and the boundary conditions are summarized in Table 5-1.
Figure 5-8 illustrates the streaklines in the ridged channels of some cases listed in Table 5-
1. It's clear that the variation of flow recirculation is similar to that observed in a wavy channel.
In the two extreme cases (Figures 5-16a and 5-16g), flow recirculation is rarely observed from
the streaklines. While in cases where K is a moderate number (Figures 5-16b to 5-16f), the
circulating streaklines become obvious, implying the presence of flow recirculation. Based on
the simulation results, with current ridged channel geometry, flow recirculation is significant
when K is in the range from 1.8 to 20, and it reaches strongest state when K approximates 4.5,
where the net flow rate is roughly about zero in the channel.
5.2.5 Experiment Validation
To validate the numerical predictions of flow recirculation in ridged channels, a set of
experiments are conducted on the ridged channels. The fabrication and parameter of ridged