Validation of hydrodynamic and microbial inactivation models for UV-C treatment of milk in a swirl-tube ‘SurePure Turbulator™’

• The PEPT technique has been applied to determine the hydrodynamic performance.
• This study shows that the surface refreshment is enhanced when the fluid viscosity is increased at constant flow rate.
• These results have been used to calculate “corrected” residence times for each fluid in the Turbulator™.
• Both first order and Weibull distribution inactivation models have been developed.
• The models enable a more accurate estimation of the required UV energy for the inactivation of the microorganisms.

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™ 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™ 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.