Bubble formation by water release in nozzles---I. Mechanisms

The aim of this study is to understand the mechanisms involved in the formation of bubbles obtained by the release of pressurized water through a nozzle in the dissolved air flotation process. To do this, nozzles were simulated by glass tubes with a constriction (Reynolds tubes). A micro-cinematographic technique was used to visualize the phenomena of release in the restriction of the Reynolds tubes. The influence of the surface energy of these tubes and of the presence of NALCO polyelectrolytes in the water on the release phenomena were studied. Gas pockets appear when pressurized water is released. These pockets form in the liquid phase if the tubes are hydrophilic. On the other hand, they appear at specific points of the tube surface when the tubes are hydrophobic. In both cases, the shape of the pockets is greatly dependent on the conical divergence angle, β, of the Reynolds tubes. These mechanisms of pressurized water release are not influenced by the presence of NALCO polyelectrolytes.