Bubble evolution

The bubble dynamics in a confined space, in particular in micro-channels, is quite different from that in infinity still fluid. In micro-channels the bubble evolution depends on a number of different factors such as existence of solid walls restricting bubble expansion in the transversal direction, a large gradient of the velocity and temperature field, etc. Some of these problems were discussed by Kandlikar (2002), Dhir (1998), and Peng et al. (1997). A detailed experimental study of bubble dynamics in a single and two parallel micro-channels was performed by Lee et al. (2004) and Li et al. (2004). 

In a fume hood, dissolve 125 mg of sodium cyanoborohydride in 1ml water (makes a 2M solution). Caution Highly toxic compound handle with care. This solution may be allowed to sit for 30 minutes to eliminate most of the hydrogen-bubble evolution that could affect the vesicle suspension. 

The value of the first constant a in equation (11) depends on the unit of current chosen, and workers have usually not troubled to record it explicitly. If we make the approximate assumption that bubble evolution occurs at equal current densities for all metals, then the differences between the values of a for the... 

A time sequence of bubbling from such a calculation of the IGT six-inch EGO-33 run is shown in Figure 3. The sequence is that of a stationary or quasi-steady pattern of bubble evolution subsequent to the start-up transient. In each individual "frame" of the time sequence a reactor section, bounded by the centerline axis on the left and the reactor radius on the right, is shown. The representative particles are indicated by the black dots while the bubbles and the voids are white. The time corresponding to discrete frames is indicated on the base of the figure and the rise of the bubbles, together with the solids mixing, can be discerned in that sequence of frames. This... 

Figure 3. Time sequence of bubble evolution during steam oxygen gasification in IGT 6-in. diameter bench scale reactor...

Since the point of bubble evolution represents a more or less indefinite rate of discharge of hydrogen and hydroxyl ions, recent work on overvoltage has been devoted almost exclusively to measurements made at definite c.d. s it is then possible to obtain a more precise comparison of the potentials, in excess of the reversible value, which must be applied to different electrodes in order to obtain the same rate of ionic discharge in each case. The details of the methods of measurement and a discussion of the results will be given after the general problem of the mechanism of electrode processes has been considered. 

Figure 3 A schematic of bubble evolution after entrainment into the upper ocean (Woolf, 1997) (reproduced by permission of Cambridge University Press from The Sea Surface and Global Change, 1997, pp. 173-205).

H. Matsushima, Y. Fukunaka, K. Kuribayashi, Water electrolysis under microgravity Part II. Description of gas bubble evolution phenomena, Electrochimica Acta, Volume 51, Issue 20 (2006) pp4190-4198... 

R. Wtithrich, Ch. Comninellis, H. Bleuler Bubble evolution on a vertical electrode under extreme current densities, Electrochimica Acta 50 (2005) pp5242-5246... 

In order to avoid calculating the whole transient process, steady state flow and MITReM conditions are calculated first. From this situation on the simulation of time dependent bubble evolution is started. A two-way interaction between bubbles and flow is considered. This means that the combined effect of the influence of the fluid flow on the bubble trajectories and the effect of the bubble movement on the fluid flow is taken into account. In figure 4 simulated situations at several time steps are shown. The mean flow is 0.2 m/s. The cathode is on the right. 

Hydrogen bubble evolution can provide a stirring effect and lead to a substantial bubble raft at the free surface of the solution. 

The temperature of a molten metal is of significant importance for the active occurrence of ultrasonic degassing. The higher is the melt temperature and the lower is its viscosity, p, the higher is the rate of acoustic streams and the easier is the process of gas bubble evolution. However, there is the optimum temperature—temperature increase above 750 °C adversely affects the efficiency of the process due... 

During combustion of the mineral rich coal particles in the pulverized fuel flame, ash envelopes may be created which can take the form of censopheres as shown in Figure 7c and d. The gas bubble evolution leading to cenosphere formation (16,22) and fly ash usually contains between 0.1 and 2 per cent by weight of the lightweight ash. The mineral rich coal particles may leave the combustion ash residue also in the form of plerosphere (spheres-... 

Figure 18.14 Scheme of bubble evolution and pressure change with time. 

In order to estimate the gas film formation time, the bubble evolution equation (3.61) is used. For simplicity, it is considered that the inter-electrode resistance R 6) may be estimated using ... 

Recalling that R(0)A(l—Q)jlocal=R(6)I=U— Ud and introducing the normalised time t — t/Atb, one gets the normalised bubble evolution equation ... 

Let us solve this equation for a voltage step input in order to estimate the gas film formation time. For terminal voltages lower than the critical voltage U < 1), the normalised bubble evolution equation can be written as (using the approximation smax —> oo) ... 

Phenomena that arise in these materials include conduction processes, mass transport by convection, potential field effects, electron or ion disorder, ion exchange, adsorption, interfacial and colloidal activity, sintering, dendrite growth, wetting, membrane transport, passivity, electrocatalysis, electrokinetic forces, bubble evolution, gaseous discharge (plasma) effects, and many others. 

The creation and destruction of charged interfaces between ionic, electronic, and dielectric materials is a central problem where electrochemical principles should be brought to bear. Phenomena embraced in this area include deposition and dissolution, growth of dendrites, bubble evolution, wetting, sintering of ionic solids and ceramic powders, and phase stability. 

The effect of mass and heat transfer associated with the problem of the bubble evolution is also very interesting. In the case of mass transport, we can assume that at a given current density, or flux, N number of the adsorbed bubbles can be formed. At a given time tR, the diameter reaches a critical value rh after which it breaks off. We assume that the fresh electrolyte arrives at a similar concentration of that of the bulk, especially when the convective flux is large enough. We also consider that the mass transport is rate determining, so when the new electrolyte arrives it rapidly converts into the product. Under this consideration, it follows the second Fick s law ... 

Similar equations can be derived for heat transfer during the bubble evolution to those of mass transfer. For a negligible coverage, we will have... 

Previous real-time studies of ramified electrodeposited formations were performed in two-dimensional cells due to the depth of focus problem while using optical microscopy. The role of hydrogen bubbles could not be investigated in detail since the bubbles in two-dimensional electrodeposition cells markedly retard the development of ramified electrodeposits. On the contrary, our experimental approach enabled us to monitor hydrogen bubble evolution and the related Zn deposit morphological changes in 3D and with no restrictions on the electrodeposition geometry. 

Foam flow in porous media is a complex, multifaceted process. Macroscopic results are the ensemble average of many pore-scale events that lead to bubble evolution and pore-wall interaction during multiphase flow. Foam in porous media is best understood when the undergirding pore-level phenomena are elucidated and quantified. 

Electrolytic gas evolution is a dynamic phenomenon affected by interactions among all the process variables. The interaction of the potential, electrode, and electrolyte not only determines the rate at which gas is evolved, but also affects the contact angles of the bubbles that determine, in conjunction with the electrolyte surface tension, the fundamental forces binding the bubbles to the electrode. Since the process occurs at a surface, small quantities of impurities may have a large effect. The dynamics of bubble evolution... 

Figure 14. Effect of gas bubble evolution on the thickness of the diffusion layer, from Ibl et al.91...

Figure 15. Effect of gas bubble evolution on the thickness of the diffusion layer, from Janssen and Hoogland.27 (Reprinted with permission from Electrochimica Acta 18, L. J. J. Janssen and J. Hoogland, The effect of electrolytically evolved gas bubbles on the thickness of the diffusion layer—II, Copyright, 1973, Pergamon Press.)...

Przybylek P. A comparison of bubble evolution temperature in aramid and cellulose paper. In 2013 IEEE International Conference on Solid Dielectrics (ICSD). Institute of Electrical and Electronics Engineers 2013. p. 983-6. ISBN 978-1-4673-4461-6. 

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