Ultraviolet light-emitting diodes (LEDs) offer advantages over mercury lamps, but their directional emission demands precise alignment with reactor hydrodynamics for effective disinfection. Conventional reactor designs often overlook hydraulic short-circuiting, where fast streamlines bypass high-radiation zones. This study establishes a targeted placement strategy that passively aligns the radiation field with velocity profiles in U-shaped and S-shaped photoreactors. We employed a validated computational framework, coupling computational fluid dynamics with ray-tracing, to identify optimal LED configurations that intercept high-velocity zones. Experimental biodosimetry using Escherichia coli was conducted in a custom-fabricated U-shaped reactor to validate the microbial inactivation efficiency. The numerical model showed strong agreement with these empirical results. Results showed that optimal LED placement is governed by the interaction between reactor geometry and flow regime. Sensitivity analysis confirmed robustness to varying LED angles and reflectivity. High-reflectivity materials, however, require optimized placement to improve performance. In U-shaped reactors, high flow rates required shifting LEDs toward the outer wall to address stratified flows, increasing inactivation by 30%, whereas low flow rates required a hybrid arrangement to match developing profiles. The S-shaped reactor was even more sensitive to optimization. A bottom-aligned configuration maximized performance in the double-curved geometry, doubling disinfection at low velocities. Overall, aligning light sources with hydraulic patterns effectively mitigates short-circuiting.
Hassanpour et al. (Mon,) studied this question.