Work

Quantitative characterization of flow regimes in continuous oscillatory baffled reactors using PIV and POD analysis

Year: 2026

Type: article

Abstract: Continuous Oscillatory Baffled Reactors (COBRs) are proven equipment for process intensification, yet their efficient design and operation in industrial applications have been hindered by a limited understanding of their complex hydrodynamics. For a long time, COBR flow regimes have been characterized using qualitative, visually based criteria, such as flow asymmetry, and guided by approximate thresholds from the literature. However, these are often insufficient for correct operation and operating parameters are then adjusted empirically. This study provides a rigorous, quantitative analysis of flow regimes in the COBR under varying net (Re net = 0–20) and oscillatory (Re o = 0–1543) Reynolds numbers using Particle Image Velocimetry (PIV) measurements. A phase-resolved analysis of the velocity fields was conducted using a combination of Proper Orthogonal Decomposition (POD) and the Hilbert transform. Flow regimes were identified via turbulence kinetic energy ( k ) levels and using the Fast Fourier Transform (FFT) of POD temporal coefficients, which provided spectral “fingerprints” for each state. Based on these metrics, the three flow regimes were quantitatively characterized: (1) laminar flow with near-zero k and a flat temporal spectrum; (2) transitional flow exhibiting intermediate k and a super-harmonic-rich temporal spectrum; and (3) turbulent flow high k and a chaotic broadband spectrum. Further parametric analysis demonstrates that transitions between these regimes depend on a complex interplay between oscillation frequency ( f ) and amplitude ( x 0 ). Increasing amplitude modifies the flow patterns from oscillating vortices to penetrating jet-like flows, although axi-symmetrical vortices can persist at high amplitudes if coupled with low frequencies oscillations. Flow instabilities are found to be more readily driven by an increase in oscillation frequency than oscillation amplitude, due to higher local fluid acceleration. In addition, Re o alone is insufficient to characterize the flow regime; for the same Re o, the flow regime can be different when obtained with high-frequency/low-amplitude oscillation conditions compared with low-frequency/high-amplitude oscillation conditions. This means that the design guidelines and the Re o thresholds for different flow regimes in COBRs provided in the current literature may not always hold.

Source: Chemical Engineering Science

DOI: 10.1016/j.ces.2026.125290

Authors: Rita Branco, Margarida S.C.A. Brito, Martine Poux, Joelle Aubin