The conduits of steady state autocatalytic plumes Physical Review E, 77, 026105 (2008). Michael C. Rogers [1], Mick D. Mantle [2], Andrew J. Sederman [2], Stephen W. Morris [1] [1] Department of Physics, University of Toronto, 60 St. George St., Toronto, Ontario, Canada M5S 1A7. [2] Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, CB2 3RA, UK

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.

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