Modelling flow-distributed oscillations in the CDIMA reaction

The development of spatial patterns ('flow distributed oscillations') in a model representing the chlorine dioxide-iodine-malonic acid (CDIMA) reactio n is investigated analytically and numerically. Flow distributed oscillatio ns arise in a plug-flow reactor (PFR) for which the inflow concentrations o f the various reacting species are maintained at appropriate constant value s. Unlike other situations, the patterning here does not require any differ ence in diffusion coefficients for the different species. The patterns are, however, closely related to operating conditions for which the same chemic al system would show temporal oscillations in a well-stirred batch reactor. As the flow rate through the PFR is varied, the system undergoes a sequenc e of transitions from absolute to convective instability and subsequently t o stationary patterns. The onset of stationary patterns is found to be subc ritical, so there is a range of operating conditions for which there is bis tability between a stationary pattern and an essentially uniform state. The results indicate that these patterns occur for conditions that should be r ealisable experimentally and that typical wavelengths of the patterns would be of the order of 0.1 mm.