UV-disinfection reactors may appear in a variety of forms, but it is useful for all types to identify the inflow and outflow zones (those in which the fluid approaches or, respectively, recedes from the radiation source) and the direct radiation zone (in which the flow occurs along the UV lamp). Due to the spatial variability of the velocity field and the radiation intensity, the radiation doses received in different zones of a reactor differ. In this work, theoretical considerations regarding functions describing the variability of UV radiation doses in flow reactors are presented. The most basic parameter of a UV-disinfection reactor is the minimal time required by the fluid to pass through the reactor. Such time depends on the maximum fluid velocity in the reactor. Based on the theoretical analysis of this phenomenon, the doses in different zones of the reactor have been compared for laminar and turbulent flows. The result of the analysis states that UV-disinfection reactors should be designed in such a way to deliver the required amount of radiation to the point at which the fluid velocity is the highest. The other main conclusion resulting from this comparison yields that the most effective in terms of disinfection is the direct radiation zone, whereas the influence of the inflow and outflow zones is negligible.
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