Buoyant Plumes and Vortex Rings in an Autocatalytic Chemical Reaction

Buoyant plumes, evolving free of boundary constraints, may develop well-defined mushroom-shaped heads. In conventional plumes, overturning flow in the head entrains less buoyant fluid from the surroundings as the head rises, robbing the plume of its driving force. We consider here a new type of plume in which the source of buoyancy is an autocatalytic chemical reaction. The reaction occurs at a sharp front which separates reactants from less dense products. In this type of autocatalytic plume, entrainment assists the reaction, producing new buoyancy which fuels an accelerating plume head. When the head has grown to a critical size, it detaches from the upwelling conduit, forming an accelerating, buoyant vortex ring. A second-generation head then develops at the point of detachment. Multiple generations of autocatalytic vortex rings can detach from a single triggering event.

Figure 1

A schematic of the apparatus. The main volume is a cylinder 32 cm long with an inner diameter of 8.9 cm. The capillary tube has an inner diameter of 2.7 mm.

Figure 2

A sequence of images showing the evolution of the plume structure. (a) 202 s, (b) 328 s, (c) 458 s, and (d) 554 s after release.

Figure 3

The growth of the plume as a function of time, showing (a) the width of the head, and (b) its height. Lines in (a) show the nearly linear evolution of the width in the three regimes indicated. Vertical arrows indicate the positions of images (a), (b), and (c) from the previous figure.