This study reports flow visualization and measurements of the
enhanced mixing that is effectively achieved by introducing pressure
disturbance in a double T-junction micromixer. The disturbance of
sinusoidal waveform was introduced through the perturbation channels with
either symmetric or asymmetric arrangement. Quantification of the mixing
efficiency is based on the color change resulting from the chemical reaction
of two species, one is ferric chloride and the other is ammonium thiocyanate,
contained in the two the streams for mixing. The mixing efficiency was
measured as a function of oscillation frequency in a range of 2-60 Hz while
maintaining the oscillation amplitude constant for flow rates between 5-15
mL/hr. It is found that the mixing efficiency grows with increasing
frequency in the lower frequency range until reaching a maximum that can
be as much as nearly ten times the undisturbed case. Then a further increase
of the frequency may lead to reducing or retarding the growth. In the cases
of asymmetric disturbance, the maximum mixing efficiency occurs at higher
frequency for larger flow rate. It is also found that the mixing efficiency can
be effectively raised with increasing disturbance amplitude, and the
symmetric disturbance seems more effective in enhancing the mixing than
the asymmetric disturbance.