Forced convective structures in a differential-flow reactor

A model of an autocatalytic reaction in a differential-flow reactor is cons idered in which the reactant is immobilized and the autocatalyst allowed to flow (with uniform velocity) and to diffuse. Consideration is given to the influence that a periodic external signal (fluctuations in the inflow conc entration of the autocatalyst) can have upon the convective structures whic h exist in this model. It is shown that, depending on the frequency of the signal, there are two parameter regions giving distinct spatio-temporal res ponses. There is a region of high excitation waves (convected forced waves) which appear for a finite range of frequencies. Outside this range there a re two domains of natural response waves. Close to the boundary of these re gions there are irregular responses suggestive of an excitable system: pack ets of travelling waves of complex form develop which appear at non-regular intervals surrounded by small amplitude periodic waves.