Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

We studied the bubble formation at micro-scale orifices in the range from 0.03 mm to 0.193 mm under the constant gas flow conditions. Furthermore, we investigated the evolution of individual forces applied on the bubble surface during its formation. We observed a different mechanism of the bubble formation compared with millimeter range orifices. This mechanism is highly influenced by the capillary pressure and gas kinetic energy. The latter results in a sequence of coalescence events of the bubbles in the vicinity above the orifice, even at significantly low gas flow rates. Studying the individual forces acting on the bubble revealed that the mechanism of bubble formation at micro-orifices is highly dependent on the gas momentum force and the liquid inertia force. Accordingly, we propose a new mechanistic model that precisely predicts the bubble size generated at micro-orifices. In addition to the influential forces, the model includes the influence of both the bubble base expansion and the relative bulk liquid velocity. Experimental validation of the model confirms that the maximum relative error of the model is less than 10%.