An Oscillatory Flow Reactor with Converging-Diverging Units and Its Single-Phase Hydrodynamic Characterization

Under laminar flow conditions, oscillatory flow reactors (OFRs) enhance mixing and mass transfer by superimposing periodic oscillations onto a net flow. However, conventional baffled OFRs are constrained by localized high shear stress, inefficient mixing regions, and elevated energy consumption. To overcome these limitations, this study introduces a novel converging-diverging OFR featuring smooth intercell transitions, inspired by the venturi tube design. A combined experimental and numerical approach is employed to systematically evaluate the key performance characteristics of this novel configuration. Notably, even in the absence of oscillation, the reactor achieves near-ideal plug flow behavior at a net flow Reynolds number (Ren) of 346, with a corresponding dimensionless axial dispersion coefficient (Dax*) of 0.0096. Flow field simulations confirm that the converging-diverging structure eliminates inherent stagnant zones and operates at a cycle-averaged fluid shear rate approximately 12% lower than the single-orifice baffled OFR. In addition, the pressure drop per cell is reduced to less than half of that in the conventional design. An oscillatory frequency in the range of 0.5–1.5 Hz is recommended for optimal performance. While oscillatory flow enhances fluid mixing within the reactor, the net flow rate remains a critical factor determining the upper limit of mixing performance. Importantly, under moderate net flow conditions, the system can attain an ideal mixing regime with the aid of appropriately tuned oscillations.