Advanced CO2 bubble flow analysis in DFAFC: Quantifying volume density distribution and gas volume fraction using a transparent fuel cell

• Quantitative CO 2 bubble analysis in transparent DFAFC. • CO 2 volume density distribution analysed across multiple cell orientations. • Vertical-horizontal cell orientation exhibits the best performance. • CO 2 accumulation/removal balance determines DFAFC performance. • Volume fraction analysis reveals cyclic patterns in two-phase flow. The increasing focus on direct liquid fuel cells as promising power generation devices has highlighted the critical challenge of gas management within these systems. This study introduces a novel quantitative approach to analysing CO 2 bubble dynamics through real-time visualisation using a transparent direct formic acid fuel cell (DFAFC) fabricated through combined 3D printing and CNC milling techniques. Our methodology quantifies bubble behaviour through two key metrics: bubble and slug volume density distribution determined for one-second intervals and CO 2 volume fraction time evolution across multiple cell orientations and flow field configurations (serpentine and serpentine with right-angled trapezoidal baffles). While visual observation alone usually fails to distinguish significant differences between orientations, our quantitative analysis over 30-second periods revealed crucial performance variations. The results demonstrated that DFAFC performance is fundamentally governed by the balance between CO 2 resultant accumulation and removal rates rather than absolute CO 2 content. The vertical-horizontal orientation exhibited superior performance among tested configurations, followed closely by the vertical–vertical orientation. The CO 2 volume fraction time evolution analysis revealed distinct cyclic behaviour in gas accumulation and removal, providing new insights into the dynamic nature of two-phase flow patterns. The findings provide directions in optimising gas removal systems and cell architecture, particularly through developing hydrophilic electrode surfaces for reduced bubble adhesion and leveraging vertical-horizontal fuel cell operation to utilise buoyancy forces in gas removal systems. Our methodology could be valuable for future studies of complex interconnector geometries.