A numerical model, i.e. dispersed phase model (DPM), has been developed to describe the particle phase flow patterns and particle residence times in thin-film UV reactor Cider Sure 1500. This model, along with UV intensity model, has been used to simulate processing of apple cider. Fluent 5 CFD code was used to solve all the governing equations. The physical properties of the apple cider such as density, viscosity, total solid weight fraction and solid phase characteristics (particle size, shape, size distribution and volume fraction) were measured. These properties were included to our numerical model as inputs. The results of our simulations for the UV reactor were compared with experimental biodosimetry data. Reasonable agreement was observed between simulation and experimental UV dose values. The model also predicted that most of the particles were received UV dose less than the average value reported by manufacturer of the UV lamps. Based on the simulations and the experimental observations, the modification of the design of the UV reactor Cider Sure 1500 were suggested. (C) 2004 Elsevier Ltd. All rights reserved.