A computational fluid dynamics model, coupled with a discrete ordinate radiation model, was developed for a channelled optical fibre reactor (COFR) and used to optimise its channel configuration. Air channels were grouped according to their location in the COFR into: inner arc, intermediate arc and outer arc. The flow field in the COFR was laminar with similar velocity vector distributions in all channels irrespective of their location in the COFR cross-section. The computational results demonstrated TiO2 coatings on the channel walls received light increasingly in the order: outer arc > intermediate arc > inner arc. The radiation distribution on the TiO2-coated channel walls was governed by the spatial distance. The ethylene conversion distribution corresponded well with the radiation distribution with channels in the inner and the outer arcs showing the lowest and the highest conversion, respectively. The simulation results agreed well with the experimental data possessing Pearson correlation coefficients of 0.995, 0.997 and 0.997 for variations in the incident radiant power, gas flow rate and initial ethylene concentration, respectively. Six alternate channel configurations were considered for optimising overall ethylene conversion in the COFR with an improvement of upto 33% being achieved. (C) 2010 Elsevier Ltd. All rights reserved.