The Positron Emission Particle Tracking (PEPT) flow visualisation technique has been applied to determine the hydrodynamic performance of a full-scale transparent model of a SurePure Turbulator (TM) used for the microbial treatment of turbid dairy fluids using UV-C radiation. The effect of flow rate upon the refreshment of fluid at the surface of the UV source has been investigated using two model fluids each possessing the same viscosities as milk and cream respectively. The amount of surface refreshment is modelled as a time density function close the surface of UV-C source and incorporated into an existing first order microbial inactivation model and a Weibull distribution model. Fitting to experimental data obtained for the inactivation of selected milk pathogens using the Turbulator (TM) have demonstrated the superiority of the Weibull model. These models enable a more precise estimation of UV-C energy requirement for the inactivation of the milk borne pathogenic organisms to be made since the amount of surface refreshment affords a significant performance enhancement. (C) 2015 Elsevier Ltd. All rights reserved.