Analysis of ultraviolet energy distribution in UV disinfection systems using Monte Carlo Ray-Trace method.

摘要

Determination of fluence rate in ultraviolet (UV) disinfection systems is a crucial part in evaluating disinfection efficiency of the systems. A robust Monte Carlo Ray Trace (MCRT) method has been developed to determine fluence rates in three-dimensional space of the systems. This is a statistical sampling method in which millions of random light energy bundles are simulated from the axis of each UV lamp and traced through the system until their energies reduce to a minimum threshold level. Inherent phenomena including refraction through quartz tubes, specular reflection at quartz tube surfaces, and absorption by quartz and water, along with specific geometric factors of model systems, are addressed in the MCRT algorithm. Each time the MCRT algorithm is executed, millions of independent random samples are recorded. In spite of the inherent randomness of the simulation process, consistent fluence rates throughout the UV systems under study were obtained. Fluence rate data in the radial direction from modeled lamps compared well with observed experimental data obtained from two independent sources and with results from the Point Source Summation model. Based on data obtained from the MCRT simulations for modeled UV systems with multiple rows of low pressure UV lamps, fluence rates in the space between lamps located inside the lamp bank are significantly higher than those in space located outside the lamp bank and along channel walls. This is primarily due to the energy contributions of surrounding lamps. The results also suggest that the effects of reflections from quartz tube surfaces and changes in lamp spacing to the distribution of fluence rates in the systems under study are insignificant, primarily due to the fact that fluence rates of each individual lamp drop significantly at the radial distance beyond a few centimeters from the quartz tube surface closer to the surface.