Development of a CFD-based model for simulation of UV-LED reactors for water treatment (2019)
The ultraviolet light emitting diode (UV-LED) has recently emerged as a new UV source. It offers design flexibility due to its small size and ability to alter its radiation profile. In view of the variety of design possibilities for a UV-LED reactor, a computational model could be of great value for simulating the reactor and providing insight into its performance. Given the UV-LED’s ability to emit various radiation wavelengths and because it is a directional UV source, the challenges of simulation for UV-LEDs are greater than those for UV lamps, which typically have a single wavelength and an almost radial radiation profile. This study proposes a method of simulating UV-LED reactors for water treatment in the Eulerian framework through the integration of the kinetic, hydrodynamic, and radiation models, representing UV-LED systems. Additionally, the concept of an ideal UV-LED system is proposed, which can provide insight into the efficiency of any UV-LED reactor design concept. In this study, UV-LED is modeled as a polychromatic point source with a specific radiation profile. The radiant energy field of a UV-LED reactor is developed by considering the absorption of media, refraction and reflection at air-quartz-water interfaces, and the reflection from the internal wall surfaces. The developed radiation model was applied to different UV-LEDs, and the numerical predictions were successfully evaluated using actinometry and radiometry. The radiation model was employed to obtain the kinetic rate constants of the challenge microorganisms (e.g., Escherichia coli and MS2) suspended in water, and biodosimetry results showed that modifying microorganisms’ 254 nm fluence-response data based on the germicidal efficiency of UV-LED could yield acceptable kinetics information. Therefore, during the development of the integrated model, the germicidal factors of UV-LEDs were used to homogenize the germicidal radiant power outputs of UV-LEDs. The integrated model of reactor performance was evaluated through experimental studies of the challenge organisms in two UV-LED reactors under different operating conditions, including flow rates, flow regimes, radiant powers, and UV-LED configurations. The integrated model could predict the overall reactor performance and provide information that enabled to improve the efficiency 10 times.