Performance assessment, through numerical simulation and experimental evaluation, of a thin-film ultraviolet reactor for the processing of fruit juices

The paper presents a numerical approach to investigate the performance of a thin-film ultraviolet reactor in treating three different fruit juices (apple, orange and pineapple) with UV-C radiation, under six flow rate conditions. Minimum, average and maximum doses were calculated for each configuration, by integrating, over time the irradiance over one thousand different streamlines. The presented approach allows for calculating the dose distribution achieved, thus assessing both the fulfilment of regulatory requirements and the uniformity of the treatment. Experimental tests were finally performed on both apple and orange juice, with a flow rate of 80 L/h. For apple juice, more than 3 Log CFU/mL reductions were obtained on Escherichia coli ATCC 11,229, while, for orange juice, a negligible reduction (0.05 Log CFU/mL) was achieved. These results, according to biodosimetry data from other studies, correspond to UV-C dose distributions that confirm those calculated.