Development of a hydrodynamic model for the UV-C treatment of turbid food fluids in a novel 'SurePure turbulator™' swirl-tube reactor

The hydrodynamic performance of a Surepure Turbulator™ used as an ultraviolet (UV) light source to give microbial reduction in turbid food fluids such as milk has been determined using Particle Image Velocimetry and Positron Emission Particle Tracking (PEPT). A microbial reduction model has been developed using the PEPT data, based on construction of a fractional time density as a function of distance from the UV source. The novel swirl tube design employs a tangential inlet to impart a swirling motion which promotes refreshment of fluid at the surface of the UV source; the experiments performed show this property is a strong function of flow rate and inlet geometry. Enhanced performance is predicted for the device compared with a simple plug flow model at the design flow rate, corresponding to a 100% improvement in the predicted microbial kill. At 75% turndown, the swirling motion is less significant and the device reverts to close to plug flow behaviour. Industrial relevance: UV light has been proposed as a way of reducing the microbial load of a fluid. In turbid fluids, however, the attenuation of the UV is such that only thin films can be treated. This paper considers the design of a candidate UV processing method for such fluids in which the fluid is mixed such that it spends only a short time at the surface next to the UV source, and is thus fully processed. The practical need is to find out how effective mixing is, and what level of microbial reduction would be expected. © 2011 Elsevier Ltd. All rights reserved.