Conduits of steady-state autocatalytic plumes
Michael C. Rogers, Mick D. Mantle, Andrew J. Sederman, and Stephen W. Morris

Plumes are typically formed when a continuous source of buoyancy is supplied at a localized source. We studied laminar plumes where buoyancy is supplied by an autocatalytic chemical reaction: the iodate - arsenous acid (IAA) reaction. The nonlinear kinetics of the IAA reaction produces a sharp propagating front at which buoyancy is produced by exothermicity and compositional change. When the reaction is initiated in an unconfined volume of reactant, a starting plume with a mushroom shaped head connected to the initiation point by a long conduit is formed. After the initial transient during the ascent of the head, we observed the emergence of a steady state in the conduit morphology and flow. Autocatalytic plumes were compared to non-reacting, compositionally buoyant plumes using GERVAIS, an MRI velocimetric technique. Autocatalytic conduits had axisymmetric bimodal velocity profiles and cone-shaped morphologies, in contrast to the Gaussian profiles and cylindrical shapes of non-reacting conduits. The bimodal distribution for autocatalytic plumes is a consequence of the unique effect of entrainment in this system. Rather than the usual effect of entrainment in non-reacting plumes, where less buoyant fluid is incorporated into the plumes, entrainment in autocatalytic plumes provides a buoyancy flux along the entire conduit by means of chemical reaction, thereby delocalizing the buoyancy source.

© 2008 The American Physical Society.