arXiv subjects

E. J. Vega

Publications and source records attributed to E. J. Vega.

7 recordsLinked to original sources

arXiv2026

Enhancing hydrogen production in alkaline electrolyzers by using an ultra-fast kinetics surfactant

We study the effect of surfactant adsorption kinetics on water electrolysis performance using Surfynol 465, an ultrafast-kinetics surfactant. High-speed optical diagnostics reveal that Surfynol 465 reduces bubble residence time by an order of magnitude. Compared to the slower surfactant Triton X-100 and the surfactant-free baseline, it also prevents the growth of large bubbles ($>200\ μ$m). We validated these results on an anion-exchange membrane electrolyzer (AEMEL) test bench. Adding Surfynol 465 to the $1\text{ M KOH}$ electrolyte decreases cell overpotential by 140--150 mV. It nearly triples the current density (from 0.13 to 0.37 A/cm$^2$ at 2 V) and increases average power by 40\% during a week-long test. Furthermore, downstream corrosion analyses reveal a strong alloy-dependent response. The surfactant reduces degradation in stainless steel and brass but accelerates corrosion in carbon steel.

physics.flu-dyn↗

arXiv2026

Influence of a vertical-wall leading edge on bouncing and escape bubble rising regimes

This work investigates deformable gas bubbles rising near a vertical wall in ultrapure water, focusing on how the position of the wall leading edge affects their near-wall dynamics. Two configurations are considered: (i) a wall extending from 11--25 bubble diameters below the bubble injection point, so that the bubble rises under the continuous influence of the boundary; and (ii) a wall whose leading edge is located 144 mm above the injector, corresponding to approximately 80--180 bubble diameters, allowing the bubble to reach its terminal velocity before entering the wall-bounded region. The results show that the wall leading-edge position influences both the transition from periodic bouncing (PB) to bouncing--tumbling--escaping (BTE) dynamics and the rebound frequency within the PB regime. When the wall leading edge is placed downstream, the onset of BTE occurs at smaller bubble sizes, corresponding simultaneously to lower Bond ($Bo$), Galilei ($Ga$), and Reynolds ($Re$) numbers. The Strouhal number ($St$) follows a similar decreasing trend in both configurations at low Bond numbers, but the two behaviours diverge for ($Bo \gtrsim 0.15$). For the PB regime, when the wall extends from the injector, $St$ approaches an approximately constant value of $St\simeq0.014$, whereas substantially lower values are measured for the downstream-wall configuration. The larger rebound amplitudes and longer return stages observed in the latter configuration account for lower frequencies. These findings indicate that the bubble dynamics depend not only on the conventional control parameters and wall separation, but also on the wall geometry and the associated pre-interaction bubble hydrodynamic history.

physics.flu-dyn↗

arXiv2026

Effect of surfactant kinetics on the wetting following the drop impact onto rough surfaces

We experimentally analyze the effect of a surfactant on wetting following drop impact on rough surfaces, paying special attention to the role of dynamic surface tension. To this end, we compare the results obtained with Triton X-100, SDS, and Surfynol 465. For concentrations below the critical micelle concentration $c_{\textin{cmc}}$, the evolution of the coverage area is nearly identical for all three surfactants, suggesting that the surfactant concentration is too low to significantly influence droplet spreading. In contrast, pronounced differences emerge due to the distinct dynamic surface tensions of the surfactants at $c/c_{\textin{cmc}}=2$. The evolution of the coverage area during spreading is nearly the same for pure water droplets and those containing Surfynol 465, indicating that surfactant depletion is negligible during the rapid spreading stage. As the Weber number increases, droplet spreading becomes progressively less sensitive to surface tension, thereby reducing the influence of surfactant adsorption kinetics. Nevertheless, Surfynol 465 produces larger coverage areas than Triton X-100 and SDS. The final coverage area is governed by the quasi-static recession of the triple contact line, which is controlled by the receding contact angle. Surfynol 465 consistently yields substantially larger final coverage areas across the range of surface roughness considered in this study.

physics.flu-dyn↗

arXiv2025

Influence of surfactant kinetics on rapid interface creation via microjet impact on liquid pools

We experimentally investigate the influence of surfactant adsorption kinetics on cavity dynamics during the rapid formation of interfaces. For this purpose, we use a submillimeter jet impacting onto a surfactant-laden liquid pool much larger than the jet dimensions. Cavity retraction and closure occur on a submillisecond timescale, posing a stringent test of the ability of surfactants to reduce surface tension dynamically. Our experiments reveal the difference between the effects of sodium dodecyl sulfate (SDS), a surfactant with moderately fast adsorption kinetics, and Surfynol 465, a surfactant with ultrafast adsorption kinetics. For SDS, the collapse pathway is nearly indistinguishable from that of pure water, suggesting negligible dynamic surface tension reduction. In contrast, Surfynol allows the emergence of deeper cavities that persist longer in the liquid pool. The harmonic oscillator model accurately captures the cavity retraction in the deep seal regime. The fitted values of the damping ratios are consistent with the dynamic surface tensions.

physics.flu-dyn↗

arXiv2025

Critical bubble bursting in real water. Effect of surface-active contaminants

We study the bursting of a bubble on a liquid free surface under critical conditions, i.e., those leading to the minimum (maximum) size (velocity) of the first-emitted jet droplet. Our experiments show that a tiny amount of surfactant considerably increases (decreases) the droplet radius (velocity). The volume of the first-emitted droplet increases by a factor of 20 for a concentration that produces an insignificant reduction in the bubble surface tension. The total liquid volume ejected by the bubble increases with the surfactant concentration. Surfactant accumulates at the bubble base due to cavity bottom shrinkage and surfactant convection. The resulting reduction in surface tension narrows the region of free surface reversal. Despite this effect, the size of the emitted droplet increases due to the Marangoni stress acting on the jet surface. Marangoni stress slows down the interface of the liquid jet, delaying the detachment of the droplet. More liquid flows into the droplet, increasing the mass and energy transfer to the resulting spray. A significant increase in the droplet size is also observed with a weak surfactant. This indicates that natural water contamination can substantially alter the bursting of bubbles under critical conditions. Our results may explain the size of the particles emitted by bubble bursting in seawater.

physics.flu-dyn↗

arXiv2025

Effect of a downstream vertical wall on the rise regime of an isolated bubble: an experimental study

This work experimentally investigates deformable nitrogen bubbles rising in ultrapure water and interacting with a vertical wall, focusing on how this downstream boundary alters their dynamics, an effect critical to many real-world processes. The experiments were conducted with a fixed Morton number, $Mo = 2.64 \times 10^{-11}$, with Bond, Galilei, and Reynolds numbers in the ranges $0.08 \lesssim Bo \lesssim 0.33$, $71 \lesssim Ga \lesssim 194$, and $132 \lesssim Re \lesssim 565$, respectively. The initial dimensionless horizontal distance between the wall and the bubble centroid was systematically varied, $0.3 \lesssim L \lesssim 5$, and the bubble trajectories from two orthogonal vertical planes were captured using high-speed imaging. While the bubble rising paths were stable without the wall presence for all the cases, the results reveal that wall proximity significantly affects the rising path, depending on $Bo$ (or $Ga$) and $L$. A map with four distinct interaction regimes and their transitions is obtained: (i) Rectilinear Path (RP) at low $Bo$ and large $L$, with negligible wall influence; (ii) Migration Away (MA) at higher $Bo$ and moderate-to-large $L$, with lateral deviation from the wall; (iii) Collision and Migration Away (C+MA) at high $Bo$ and small $L$, where bubbles first collide and then migrate away; and (iv) Periodic Collisions (PC) at low $Bo$, where repeated wall impacts occur due to competing forces. These findings bridge the gap between idealised simulations and practical systems, offering high-quality data to support and refine computational models of bubble-wall interactions in industrial and environmental applications.

physics.flu-dyn↗

arXiv2025

A new emitter for electrospray and electrohydrodynamic jet printing

We propose using a dielectric beveled nozzle for electrospray and electrohydrodynamic jet printing. This nozzle stabilizes the liquid ejection of low-conductivity liquids, considerably reducing the minimum flow rate below which the flow becomes unstable. This translates into a significant reduction of the minimum jet diameter. Due to its dielectric character, electrochemical reactions occurring in metallic beveled nozzles (e.g. hypodermic needles) do not occur, preserving the purity of the liquid. This property makes this nozzle appropriate for Electrospray Ionization Mass Spectrometry (ESI-MS) or bioplotting. We illustrate the capabilities of this new technique by conducting (i) electrospray experiments with Newtonian liquids and (ii) electrohydrodynamic jet printing experiments with viscoelastic fluids. Jets with diameters around 1 $μ$m are produced with low-conductivity liquids such as octanol and glycerine. Viscoelastic threads a few microns in diameter are gently deposited on a moving substrate to print out uniform lines tens of nanometers in height. Due to the strong stabilizing effect of the beveled nozzle, the minimum flow rate and jet diameter were much smaller than the respective values obtained with the cylindrical capillary in the electrospray and electrohydrodynamic jet printing experiments. The proposed technique opens new routes for electrospray and electrohydrodynamic jet printing.

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