Hydrodynamics bubble

Bubble growth will be hmited by the containing vessel and the bubble hydrodynamic stability. Bubbles in group-B systems can grow to several meters in diameter. Bubbles in group-A materials with high fines may reach a maximum stable bubble size of only several cm. 

Gas-liquid multiphase catalytic reactions require the reacting gas to be efficiently transferred to the liquid phase. This is then followed by the diffusion of the reacting species to the catalyst. These mass transfer processes depend on bubble hydrodynamics, temperature, catalyst activity, physical properties of the liquid phase like density, viscosity, solubility of the gas in the liquid phase and interfacial tension. 

Three-phase fluidized beds and slurry reactors (see Figs. 30g-l) in which the solid catalyst is suspended in the liquid usually operate under conditions of homogeneous bubbly flow or chum turbulent flow (see regime map in Fig. 33). The presence of solids alters the bubble hydrodynamics to a significant extent. In recent years there has been considerable research effort on the study of the hydrodynamics of such systems (see, e.g., Fan, 1989). However, the scale-up aspects of such reactors are still a mater of some uncertainty, especially for systems with high solids concentration and operations at increased pressures it is for this reason that the Shell Middle Distillate Synthesis process adopts the multi-tubular trickle bed reactor concept (cf. Fig. 30e). The even distribution of liquid to thousands of tubes packed with catalyst, however poses problems of a different engineering nature. 

Systematic studies of bubble hydrodynamics based on the Dom effect were suggested by Dukhin (1983). A comprehensive study, comprising the measurement of adsorption on immobile surfaces with the calculation of the Stem potential and measurements of sedimentation potentials, should be performed with homologous series of ionic surfactant so that the condition (8.97) is fulfilled by higher homologues and the opposite condition (8.101) by the lower ones. With decreasing surface activity the condition (8.97) will be fulfilled at smaller adsorption values. This means that the lower the surface activity, the smaller should be the deviation of the electrokinetic potential from the Stem potential at respective values of adsorption. And finally, when condition (8.97) is not fulfilled the electrokinetic and Stem potentials must coincide over the whole concentration interval. 

When passing from Stokes field to the potential field of a bubble, hydrodynamic detachment forces grow / Up times. The radial velocity of the liquid flow at a distance of maximum... 

There is a direct and an indirect effect of bubble surface retardation on the tangential particle velocity. The direct influence is caused by the dependence of the bubble hydrodynamic fields on the velocity distribution along its surface. The indirect influence is caused by the effect of the inertia path of a reflected particle on its tangential velocity and by the dependence of the path on the bubble surface retardation. The directions of the two effects are opposite. At the transition from a free to a retarded surface, the liquid tangential velocity diminishes at any point and the inertia path grows, which results in an increase in the tangential particle velocity. 

These examples are presented not only to demonstrate the wide-spread application of microflotation in water purification. It is apparent that optimal technical design (selection of microflotation version and process parameters, such as volume fraction and size of bubbles, hydrodynamic conditions in flotation aggregates, etc.) strongly depends on properties of water which vary over a wide range depending on the plant contaminating the water. Even for one and the same plant waste water varies because of changing conditions of the production... 

Eroded grid holes] hole velocity too high/materials of construction/contaminants in fluid. [Excessive backmixing] [maldistribution] /[poor bubbling hydrodynamics]. ... 

Inadequate mixing] [maldistribution] /[poor bubbling hydrodynamics]. ... 

The same group further developed the model to include mass transfer effects, where mass is transferred from the gas phase to a reacting wall [84]. Given a solution for the bubble shape, it is a simple matter to include mass transfer, as this involves only the addition of a scalar equation with the flow-field kept frozen . The entire approach represents a clever use of CFD both to determine the bubble hydrodynamics and then to explore the influence of the flow on mass transfer, enabling them to generate useful data for the design of multi-phase monolith reactors. 

A complicated bubble hydrodynamics and mixing patterns require special development efforts for process scaleup. 

After nearly two decades of research, it is now generally accepted that mechanical damage of freely suspended cells is due to bubble hydrodynamics, in particular the bubble-bursting phenomena at Ihe headspace gas-liquid interface (Handa et al., 1987 Tramper et al., 1987 Handa-Corrigan et al., 1989 Oh et al., 1989,... 

Important aspects of all the models include limestone-S02 kinetics, combustion kinetics and other gas-solids reaction kinetics, gas phase material balances, solid phase material balances, gas exchange between the bubble and emulsion phases, heat transfer, and bubble hydrodynamics. 

If, however, the reservoir pressure drops below the bubble point, then gas will be liberated in the reservoir. This liberated gas may flow either towards the producing wells under the hydrodynamic force imposed by the lower pressure at the well, or it may migrate... 

A recent design of the maximum bubble pressure instrument for measurement of dynamic surface tension allows resolution in the millisecond time frame [119, 120]. This was accomplished by increasing the system volume relative to that of the bubble and by using electric and acoustic sensors to track the bubble formation frequency. Miller and co-workers also assessed the hydrodynamic effects arising at short bubble formation times with experiments on very viscous liquids [121]. They proposed a correction procedure to improve reliability at short times. This technique is applicable to the study of surfactant and polymer adsorption from solution [101, 120]. 

Cavitation has three negative side effects in valves—noise and vibration, material removal, and reduced flow. The bubble-collapse process is a violent asymmetrical implosion that forms a high-speed microjet and induces pressure waves in the fluid. This hydrodynamic noise and the mechanical vibration that it can produce are far stronger than other noise-generation sources in liquid flows. If implosions occur adjacent to a solid component, minute pieces of material can be removed, which, over time, will leave a rough, cinderlike surface. 

Particle-Bubble Attachment. In the above, principles leading to creation of desired hydrophobicity/hydrophihcity of the particles has been discussed. The next step is to create conditions for particle-bubble contact, attachment, and their removal, which is simply described as a combination of three stochastic events with which are associated the probability of particle-bubble colhsion, probabihty of attachment, and probability of retention of attachment. The first term is controlled by the hydrodynamic conditions prevaihng in the flotation unit. The second is determined by the surface forces. The third is dependent on the s irvival of the laden bubble by liq ud t irbulence and impacts by the other suspended particles. A detailed description of the hydrodynamic and other physical aspects of flotation is found in the monograph by Schulze (19 ). 

Hydrodynamics and mass transfer in bubble columns are dependent on the bubble size and the bubble velocity. As the bubble is released from the sparger, it comes into contact with media and microorganisms in the column. In sugar fermentation, glucose is converted to ethanol and carbon dioxide ... 

The overall set of partial differential equations that can be considered as a mathematical characterization of the processing system of gas-liquid dispersions should include such environmental parameters as composition, temperature, and velocity, in addition to the equations of bubble-size and residence-time distributions that describe the dependence of bubble nucleation and growth on the bubble environmental factors. A simultaneous solution of this set of differential equations with the appropriate initial and boundary conditions is needed to evaluate the behavior of the system. Subject to the Curie principle, this set of equations should include the possibilities of coupling effects among the various fluxes involved. In dispersions, the possibilities of couplings between fluxes that differ from each other by an odd tensorial rank exist. (An example is the coupling effect between diffusion of surfactants and the hydrodynamics of bubble velocity as treated in Section III.) As yet no analytical solution of the complete set of equations has been found because of the mathematical difficulties involved. To simplify matters, the pertinent transfer equation is usually solved independently, with some simplifying assumptions. 

Certain hydrodynamical problems, as well as mass-transfer problems in the presence of surface-active agents, have been investigated theoretically under steady-state conditions (L3, L4, L10, R9). However, if we take into account the fact that in gas-liquid dispersions, the nonstationary term must appear in the equation of mass- or heat-transfer, it becomes apparent that an exact analysis is possible if a mixing-contacting mechanism is adopted instead of a theoretical streamline flow around a single bubble sphere. 

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