Characterization of bi-directionally oscillating dynamic flow and frequency-dependent rectification performance of microdiffusers

This paper characterizes a bi-directionally oscillating dynamic flow in a planar microdiffuser in order to evaluate the flow rectification performance of the microdiffuser. In the theoretical study, we present a bidirectionally oscillating flow model, where the boundary layer thickness governs the flow rectification performance of the microdiffuser. In the experimental study, we fabricate two different microdiffuser prototypes, having the neck widths of 100 μm (D100) and 300 μm (D300), respectively. The prototypes, D100 and D300, show the maximum net flow rates of 116.6 μl/min and 344.4 μl/min, respectively, for an identical piezoelectric flow actuation using the sinusoidal drive voltage of 100 V p-p at 50 Hz. The flow rates measured from D100 and D300 are approximately 47% of the theoretical values estimated from the conventional unidirectional flow model for the net boundary layer thicker than the neck width. The experimental flow rate of D300, however, decreases from 47% of the theoretical values at the flow frequencies higher than 90 Hz, at which the net boundary layer thickness is reduced to the microdiffuser neck width. It is experimentally verified that the flow rectification performance and the net flow rate of the microdiffuser tend to decrease when the boundary layer thickness is smaller than the diffuser neck width