Forced convective structures in a differential-flow reactor

A model of an autocatalytic reaction in a differential-flow reactor is considered 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 concentration of the autocatalyst) can have upon the convective structures which exist in this model. It is shown that, depending on the frequency of the signal, there are two parameter regions giving distinct spatio-temporal responses. There is a region of high excitation waves (convected forced waves) which appear for a finite range of frequencies. Outside this range there are two domains of natural response waves. Close to the boundary of these regions there are irregular responses suggestive of an excitable system: packets of travelling waves of complex form develop which appear at non-regular intervals surrounded by small amplitude periodic waves.