Growth and detachment of chemical reaction-generated micro-bubbles on micro-textured catalyst

Abstract

This work investigates the growth and detachment of chemically formed micro-bubbles on micro-textured catalyst using a high-speed digital camera and simulation results. Three bubble growth stages were identified for single bubbles grown on circular type Pt catalyst. The first stage was inertia-controlled and the bubble diameter was directly proportional to time, and pertained when the bubble size was smaller than the Pt catalyst; in the second and third stages, gas was generated at a constant rate and the bubble diameter was varied as the cube root of time. However, in the third stage, the bubble growth rate is slightly lower than in the second stage, suggesting saturation. The calculation based on a mathematical model at constant gas generation rate is highly consistent with experimental results. The basic single bubble growth phenomenon was then adopted as a comparison to the bubble growth phenomena on textured catalyst structures. Experimental results revealed that a discontinuous mesh catalyst can effectively shorten the bubble detachment time when the substructures are thoroughly separated and the bubbles are larger than their initial size (*5 lm), while the concentric circular pattern does not. This study provides an insight into the growth and detachment phenomena of chemically formed micro-bubbles on catalyst of different textures, which is useful to the design of reactors for fuel cell systems.

Dissolution of carbon dioxide bubbles and microfluidic multiphase flows

“…Recently, the method of dissolving CO 2 bubbles in a medium of various acidity 26 was proposed as a route for the generation of ultra-small bubbles for biomedical applications. 27 Although liquid-gas mass transfer has been previously investigated in bubble-columns [28][29][30] and microchannels, [31][32][33][34] the microfluidic flow behavior of bubbles having a time-dependent shape has remained mostly limited to thermally and chemically induced cavitation, [35][36][37][38] particle-stabilized bubbles, 39 and dissolving liquid droplets. 40 Here, we investigate the interrelation between the dissolution of CO 2 bubbles and microfluidic multiphase flows.…”

Towards controlled bubble nucleation in microreactors for enhanced mass transport

“…For example, Neira D'Angelo et al used inert gas to induce Taylor flow in a microchannel to try to reduce mass transport limitations in APR. 19 A very similar dual scenario exists for gas evolving electrodes, as found in fuel cells 20 or other types of electrochemical reactors 21,22 for, e.g., power and hydrogen production, in which bubbles on (micro)-electrodes play an equally important role on the reactor perfomance. 23 In previous work, we numerically investigated the influence of bubbles on the momentum, heat and mass transfer for APR of a 10 wt% glycerol aqueous solution, assuming a 2Dconfiguration for a microchannel reactor.…”

“…[37][38][39] Alternatively, the surface chemistry can be altered locally to also change its wettability, for example via fluorocarbon deposition to create hydrophobic islands, 21,40,41 which in turns promotes bubble nucleation on those sites. 37 Finally, the bubble detachment size and time have been manipulated using dielectrophoresis, 42 by adding surfactants or polyethylene glycol (PEG) in the solution 22 to change the surface tension and preventing bubble coalescence, by promoting convection using a horizontal magnetic field, 22 by introducing a specific texture or patterning in the catalytic surface, 20 or by applying an ultrasonic field. 43 Furthermore, in a microreactor it is particularly important that the bubble departure radius, R d , remains smaller than the hydraulic diameter of the microchannel, to prevent the bubbles from significantly obstructing flow.…”

Self-Propelled Detachment upon Coalescence of Surface Bubbles

“…The static, advancing, and receding contact angles on the microhole patterned gold surface were 85.3 AE 4.0°, 89.7 AE 2.0°, and 19.6 AE 3.6°, respectively. The bubbles nucleated and grew out of an oxygen-oversaturated environment [42,43], being pinned at the edge of the microholes with a footprint radius R p ¼ 1 μm, which was measured by an inverted laser scanning confocal microscope (A1 system, Nikon Corporation, Japan). The bubble growth and interactions were recorded using a high-speed camera (Phantom V2512, USA) through an inverted microscope with a dry objective (Olympus, UPLFLN 20×, NA ¼ 0.5, WD ¼ 2.1 mm).…”