Saturation behavior in a bubbler-based vapor delivery system

Bubbler-based vaporizers are widely used for chemical delivery in thin-film deposition processes, yet the mechanisms governing outlet saturation remain mostly unexplored. In this work, dry N2 gas was bubbled through water in a stainless-steel bubbler at atmospheric pressure. Saturation of the outlet stream was tested as a function of inlet gas flow rate and vessel fill level. Using fast x-ray imaging, distinct bubble and coalescence regimes across operating conditions were identified. Despite these differences in bubble dynamics, outlet measurements showed near-complete saturation across all tested conditions. A simplified mass-transfer model indicated that exchange across bubble–liquid interfaces alone cannot account for the observed results. Instead, mass transfer at the liquid–headspace interface, enhanced by surface agitation and droplet entrainment, provides a substantial additional source for mass exchange. These findings highlight the importance of non-bubble interfaces in bubbler operation and suggest that models neglecting these effects may underestimate outlet concentrations.