The coiled tube reactor is the most efficient UVC reactor for disinfecting microorganisms in liquid food flow. Thus, it is critical to investigate the effective parameters for designing a coiled tube UVC reactor. In this study, CFD simulation is used to investigate the turbulent and laminar flow of Newtonian and non-Newtonian fluids. In turbulent flow, disinfection in the tube area is nearly uniform, with the exception of regions near internal lamps, where the most disinfection has occurred. The variation of log10 reduction in terms of tube turn number is linear. Increasing the non-Newtonian behavior increases the disinfection of microorganisms in the reactor. Furthermore, the effect of tube diameter on coiled reactor performance is investigated. Reducing the diameter of the reactor's tubes improves its performance. Finally, two correlations are obtained for the influence of the effective parameters on the log10 reduction of this type of reactor.