Synergistic effects of temperature and geometry on hydroxyl radical production in micro- and macroscale hydrodynamic cavitation reactors

Official URL: https://dx.doi.org/10.1016/j.cej.2026.179820

Hydrodynamic cavitation (HC) has been increasingly investigated as a process-intensification platform for advanced oxidation processes, where localized collapse events, pressure fluctuations, rapid mixing, and interfacial renewal can enhance oxidative pathways. However, the coupled effects of reactor geometry, nominal micro−/macroscale configuration, and bulk liquid temperature on the cavitation-induced oxidative activity require further clarification, particularly when true microfluidic HC reactors and macroscale benchmark reactors are compared under controlled operating conditions. This study addresses this gap by systematically evaluating the triiodide (I3−) formation in three silicon-glass microscale HC reactors and two macroscale HC reactors using the potassium iodide (KI) dosimetry. Experiments were conducted at upstream pressures of 0.69–3.10 MPa and bulk liquid temperatures of 25 °C and 45 °C. I3− formation was quantified via UV–Vis spectrophotometry and linked to cavitation dynamics through high-speed imaging and void fraction analysis. Among all configurations, the micro-venturi reactor had the best performance, achieving the highest derived I3− concentrations (peaking at 6.3 × 10−4 g L−1) and cavitation yields. Raising the liquid temperature to 45 °C consistently intensified the performance across all micro-reactors, indicating that the beneficial effects of reduced viscosity and surface tension outweighed thermodynamic suppression. By contrast, the best performing macroscale design, the multi-orifice reactor, still produced around 80%, 56.5% and 8% lower derived I3− concentrations than the micro-venturi, micro-step and long micro-diaphragm reactors, respectively, despite operating at higher specific energy inputs. Economic analysis further confirms the superior efficiency of the micro-venturi, which has up to ∼70% lower specific energy costs than the macro-reactors at the same upstream pressure. These findings provide valuable guidelines for designing temperature-optimized and geometrically refined HC reactors for enhanced oxidative environments in intensified advanced oxidation processes.