Effects of surface-active agents on bubble growth and detachment from submerged orifice

Bubble Formation in a Swirl-Venturi Microbubble Generator

“…Correspondingly, the volumetric gas flow rate into the bubble q (the blue line) stays flat at first, remains smaller than q 0 , and then increases rapidly. These changing trends are consistent with the characteristics of bubble nucleation and expansion processes shown in the literature, ,, demonstrating that in the SVMG, nucleation and expansion still exist in the beginning period of bubble formation (nucleation stage: q ≤ q 0, C does not move; expansion stage: q > q 0 , C hardly moves or fluctuates slightly at C y 0 ). However, Figure (a) also shows that the detachment stage does not occur after the expansion stage 0.48 ≤ t / T d < 0.53; conversely, the bubble experiences a second nucleation stage (0.53 ≤ t / T d < 0.96) and then expands until it departs from the orifice (0.96 ≤ t / T d < 1), in which the dimensionless volume nearly remains constant for a long time and then increases rapidly for a short time.…”

“…The reaction can only proceed after the energy reaches the activation energy; similarly, the bubble can only expand after the pressure difference Δ P breaks the barrier, and in the expansion stage and detachment stage, the pressure difference Δ P keeps dropping. Eventually, the buoyancy force dominates over the surface tension and other inhibitory forces in the detachment stage . This type of detachment stage characterized by buoyancy-induced bubble floating and departing presents concentrated detachment locations, as shown in Figure (c).…”

“…When q < q 0 , internal pressure increases; conversely, it decreases. In other words, the bubble internal pressure P b ( t ) only increases when it is in the nucleation stage . As for the liquid pressure, the changes are more complex, which can be analyzed by the liquid flow field captured by PIV, as shown in Figure (a)-(b).…”

“…Even so, the diameter of the bubbles produced by the microsized orifice is still at least twice the orifice diameter. 17,18 On the whole, for microbubbles produced by microsized nozzles and orifices, their sizes largely depend on the microsized orifice structure, and the departure bubble size is generally larger than the orifice's inner diameter, 19,20 which means a small inner diameter is required. However, there is a limitation in reducing the bubble size by decreasing the orifice and nozzle inner diameter, so researchers have to find other methods to further reduce the departure bubble size, e.g., introducing another liquid flow and establishing a shear flow field.…”

Bubble-induced convection stabilizes the local pH during solar water splitting in neutral pH electrolytes

“…While this value is added as a parameter here, in practice bubble diameter can often be controlled by the addition of surfactants or nano-structuring the electrode surface. 29,[54][55][56][57] In addition, the contact angle at the electrode surface, which is often controlled by the modification of electrocatalyst layer, has also been shown to influence the resulting bubble diameter. 40,[58][59][60][61] These approaches would therefore also positively contribute to the mass-transport of dissolved ions and the resultant concentration overpotential.…”