This paper demonstrates the effectiveness of using fibre optic micro-probes for the measurement of dispersion and mixing in continuous flow within a novel screening reactor operating under oscillatory flow conditions. The unsteady tracer injection technique was used at different oscillation conditions, with oscillation frequencies from 0 to 20 Hz and amplitudes from 0 to 3 mm (centre-to-peak). Application of optical micro-probes for on-line and real-time acquisition of experimental data allowed modelling and comparison with three different well-known non-ideal models (tanks-in-series, with no backflow; differential backmixing; stagewise backmixing) and with one two-parameter flow model (a plug flow and a stirred tank reactor in series). Model parameters were found by fitting the theoretical response with experimental data in both Laplace and time domains by different methods. An intermediate mixing behaviour (between plug flow and stirred tank reactor) was achieved in that range of oscillation frequencies and amplitudes. Dispersion was found to be dependent on the oscillation conditions (amplitude and frequencies) and related with the fluid backflow and with the breaking of flow symmetry. The discrete (stagewise) backmixing model was considered as the best model representing residence time behaviour in the small-scale tube
