Measurement of species flux from a bubble using an acousto- electrochemical technique

An acousto-electrochemical technique is presented which, for the first time, offers the potential for measuring the flux of dissolved species in a liquid resulting from bubbles of a specific chosen size in the population. Laboratory trials are presented, but the device itself was damaged in the surf zone and no data was obtained from the ocean deployment. Nevertheless, the preceding laboratory tests demonstrate the viability of the technique. The device responds to perturbations of the fluid around a small electrode. Three such sources of motion must be characterised if it is to achieve the objective stated above. First, the perturbations resulting form the translatory motions of bubbles in the liquid. To obtain bubble radius resolution in the measurement of mass flux, however, it is necessary to apply to driving (‘pump’) sound field. Bubbles close to resonance will, in addition to a translatory motion, impart to the liquid a component of mass flux at the pump frequency. This is detected. However to show that this is the result of bubble wall pulsation, and not some other coupling, the amplitude of the pump field is increased until the electrochemical sensor detects Faraday waves on the bubble wall. Not only does this prove the relation between mass flux to bubble wall motion, it provides a second route by which the radius-resolved component of mass flux might be identified. In these preliminary laboratory tests, electrochemical detection of these motions was achieved through the observation of current produced by the reduction of a suitable redox agent present within the liquid phase of the solution employed. Preparations were made to obtain preliminary data from the Hurst Spit 2000 surf zone trial, but the device was damaged by the environment.