Chemical patterns in translating vortices: inter- and intra-cellular mixing effects.

Stationary chemical patterns-flow distributed oscillations (FDOs)-are obtained when the Belousov-Zhabotinsky reaction is coupled with translating vortex flow in a Vortex Flow Reactor. For certain conditions, the FDOs are unstable with the observation of disappearing bands or complex patterns. The transitions between modes of pattern formation are reproduced in a modified Oregonator model consisting of two-zone cells connected in series. We show that increasing inter-cellular mixing of the outer zones results in a transition from FDO to absolute instabilities (AI) and increasing intra-cellular mixing between the core and outer zones can drive the reverse transition between modes (AI to FDO).

Low frequency temperature forcing of chemical oscillations.

The low frequency forcing of chemical oscillations by temperature is investigated experimentally in the Belousov-Zhabotinsky (BZ) reaction and in simulations of the Oregonator model with Arrhenius temperature dependence of the rate constants. Forcing with temperature leads to modulation of the chemical frequency. The number of response cycles per forcing cycle is given by the ratio of the natural frequency to the forcing frequency and phase locking is only observed in simulations when this ratio is a whole number and the forcing amplitude is small. The global temperature forcing of flow-distributed oscillations in a tubular reactor is also investigated and synchronisation is observed in the variation of band position with the external signal, reflecting the periodic modulation of chemical oscillations by temperature.

Inward propagating chemical waves in Taylor vortices.

Advection-reaction-diffusion (ARD) waves in the Belousov-Zhabotinsky reaction in steady Taylor-Couette vortices have been visualized using magnetic-resonance imaging and simulated using an adapted Oregonator model. We show how propagating wave behavior depends on the ratio of advective, chemical and diffusive time scales. In simulations, inward propagating spiral flamelets are observed at high Damköhler number (Da). At low Da, the reaction distributes itself over several vortices and then propagates inwards as contracting ring pulses--also observed experimentally.

Modelling complex transient oscillations for the BZ reaction in a batch reactor.

The recent observations of transient complex oscillations in the Belousov-Zhabotinsky (BZ) reaction in a batch reactor are confirmed and an attempt is made to model this behavior using the Gyorgyi-Field mechanism (an extension of the classic Field-Koros-Noyes model). It is seen that the concentration of bromomalonic acid plays an important role, acting somewhat like a "slowly-varying parameter," causing the system to sweep through a region of oscillatory response even in the absence of reactant consumption. Complex behavior is not observed in the model if the usual "pre-equilibrium" assumption in made for the intermediate species BrO(2) but does arise if a full steady-state approximation is applied to this radical. These results may bring into question some assumptions made in the usual treatment of the cerium-catalyzed BZ system in closed reactors. (c) 1997 American Institute of Physics.