Self-organising structure of bubble departures

In the paper the self-organising structure of bubble departures from nozzle outlets has been investigated. In the experiment, bubbles were generated from brass nozzles with inner diameters of 1.1 mm. They were submerged in a glass tank filled with distilled water. Three different nozzle arrangements have been considered. Correlation coefficients between signals from laser-phototransistor and pressure sensors have been calculated. It has been shown that self-organising structures of bubble departures are formed by alternative bubble departures. Their appearance significantly modifies the frequency of bubble departures and prevents departing bubbles from the vertical coalescence. When bubbles are emitted from three nozzles, the alternative bubble departures are created over each pair of neighbouring nozzles. In case of three nozzles arranged in the row, the alternative bubble departures appear on the left and right side of the central nozzle. When bubbles depart from three nozzles arranged in corners of the triangle, the appearance of alternative bubble departures over each pair of nozzles leads to appearing clockwise and counter-clockwise direction of bubble departures. It has been shown that the stability of alternative bubble departures depends on the distance between nozzles, their arrangement and the air volume flow rate. Numerical simulations show that the diagonal liquid flow (created when bubbles depart from neighbouring nozzles not at the same time) establishes 'the communication' between two bubble chains. Such 'communication' modifies conditions of liquid flow over the nozzles, the time between successive bubbles and finally, establishes the alternative bubble departures.