EFFECT OF LAMP SPACING ON UV REACTOR PERFORMANCE: COMPUTATIONAL AND EXPERIMENTAL INVESTIGATIONS

The efficiency of an ultraviolet (UV) disinfection system is a function of the electrical to radiation conversion ratio, lamp spacing and effective radiation path length, microbial action spectra, inactivation kinetics and mixing. These factors and their interactions are reviewed and the critical impact of lamp spacing on reactor efficiency is addressed.Piloting and computational studies were conducted to test UV systems with 3, 4 and 5- inch lamp spacings at different UV transmittances (UVTs). Comparisons between piloting and computational results are done at equivalent power per flow rate for 45% and 60% UVT. Results show that disinfection performance deteriorates with increasing lamp spacing. Computational predictions agree with piloting data within 16% accuracy. The computational disinfection model (CoDiM) is then used to investigate the decrease in inactivation of the 4 and 5-inch lamp spacing reactors compared to the 3-inch lamp spacing reactor as a function of UVT and lamp power setting.The comparison of the inactivation performance of the different lamp spacings as a function of lamp power indicates that for a reactor with large lamp spacing, the inefficient energy utilization caused by enlarged low-intensity regions cannot be compensated through lamp power increase.