Bubble Growth from Submerged Orifice Plates: Part 2 - Dynamic Interaction of Chamber Volume, Surface Tension, Viscous Resistance, and Wetting

Bubble growth dynamics from submerged orifices is systematically investigated in this two-part study. In Part 1, the effects of surface wettability and surface tension were examined. For a bubble growing on a hydrophobic surface, the bubble base advances and subsequently recedes prior to necking and pinch-off. The extent to which upstream gas-chamber volume influences this spreading cycle, and how that influence is modulated by liquid viscosity and surface tension, is experimentally investigated in this study (Part 2). Experiments were conducted using Teflon orifice plates (contact angle with water 105° and 128°) with diameters 0.61 < D0 < 1.5 mm. To assess chamber volume–viscosity coupling, liquids of viscosity range 0.89 < μ < 128 cP were employed, including pure distilled water, ethylene glycol, propylene glycol, and aqueous glycerol solutions. Results demonstrate that the critical capacitance number for the onset of chamber effects (NC*≈0.8−1) remains applicable even in the presence of spreading. Larger chamber volume (NC>NC*) increases bubble departure diameter when spreading is absent. However, for hydrophobic plates that exhibit bubble base spreading, introduction of chamber effects produces little to no change in departure size despite clear modifications to growth dynamics. In the absence of chamber influence, viscous suppression of spreading occurs only beyond a viscosity-dependent flow-rate threshold. In contrast, under chamber-dominated conditions, viscous effects are amplified and can eliminate spreading even at low flow rates, leading hydrophobic substrates to behave similarly to hydrophilic or capillary systems.