From Electrokinetics to Vibrofluidics: Driving Motion with Non-antiperiodic Forces

Sep 14, 2022, 4:00 pm5:00 pm



Event Description

Many types of fluid motion are induced by periodic forcings. Here we discuss what happens when you apply a periodic forcing with zero time average but broken temporal symmetry, i.e., a “non-antiperiodic” forcing, as typified by a waveform with dual frequency modes (e.g., 30 Hz and 60 Hz). Two exemplar systems are considered. First, we show how a dual-mode electric potential creates a long-range steady field in electrolytes with a mobility mismatch.  Colloids undergo net electrophoretic drift toward the grounded electrode, meaning that the direction of motion depends deterministically on which electrode is powered or grounded.  We then discuss using non-antiperiodic vibrations to move dry granular fluids in “vibrofluidic devices.”  In contrast to existing vertical vibratory methods for fluidizing granular materials that engender no net motion, here we apply a horizontal, non-antiperiodic vibratory waveform, as is readily applied with a standard subwoofer. The direction and velocity of the flow are tuned by modulating the sign and amplitude, respectively, of the vibratory waveform, with typical pumping velocities on the order of centimeters per second. Different types of granules are mixed by pumping them into Y-shaped junctions, and mixtures of granules with similar size but different friction coefficients are separated by judicious choice of the vibratory waveform.  We present asymptotic analyses of the granular fluid motion based on a frictional Froude number, and we discuss the implications for “dry” lab-on-a-chip technologies.