Bubble Phenomena

Increasing surfactant concentrations in the aeration cell has been found to decrease bubble diameter, bubble velocity, axial diffusion coefficient, but increase bubble s surface-to-volume ratio, and total bubble surface area in the system. The effect of a surface-active agent on the total surface area of the bubbles is also a function of its operating conditions. The surfactant s effect is pronounced in the case of a coarse gas diffuser where the chances of coalescence are great and the effectiveness of a surface-active solute in preventing coalescence increases with the length of its carbon chain. 

The mechanics and applications of multiphase flow has been an area of continuing interest to chemical, environmental, and civil engineers (23,77). The multiphase flow patterns may be classified as bubble flow, plug flow, stratified flow, wave flow, slug flow, annular flow, spray flow, and froth flow. Typical sketches of these various flow patterns are shown in Fig. 3. They are self-explanatory. In the field of absorptive bubble separation processes, only multiphase bubble flow and froth flow are of interest to the process engineer. 

Type of flow pattern(s) involved in an adsorptive bubble separation system depends on the type of process used. For example, bubble fractionation involves two-phase (gas-phase and liquid-phase) bubble flow, while solvent sublation involves multiphase bubble flow in their vertical bubble cells. Foam fractionation involves a two-phase bubble flow in the bottom bubble cell, and a two-phase froth flow in the top foam cell. However, all froth flotation processes (i.e., precipitate flotation, ion flotation, molecular flotation, ore flotation, microflotation, adsorption flotation, macroflotation, and adsorbing colloid flotation) involve multiphase bubble flow and multiphase froth flow. 

All batch adsorptive bubble separation processes involve no net movement of liquid, but steady bubbling of gas through the stagnant liquid. The relative bubble velocity in the bubble cell is the function of buoyancy component and the superficial gas velocity. 

The bubble size distribution in a bubble flow is primarily dependent on the rate of air supply to the gas diffuser. The size of the largest bubbles may change somewhat with the rate of air discharge and orifice size. When the liquid moves relative to the orifices, the maximum bubble diameter is equal to 2.4 times the square root of the gas-flow rate per jet divided by the liquid velocity. However, the size distribution of bubbles below the largest can be obtained only from experiment. 

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The heat transfer coefficient (/i) has been determined by measuring the temperature difference between the immersed heater and the bed. The h value increases with increasing Ug (Fig. 1(a)), but exhibits a maximum value with increasing (Fig. 2(a)). The effects of Ug on h is dominant, since the bubbling phenomena become more vigorous due to the... 

Prosperetti A (1984) Bubble phenomena in sound fields part two. Ultrasonics 22 115... 

In system 1, the 3-D dynamic bubbling phenomena in a gas liquid bubble column and a gas liquid solid fluidized bed are simulated using the level-set method coupled with an SGS model for liquid turbulence. The computational scheme in this study captures the complex topological changes related to the bubble deformation, coalescence, and breakup in bubbling flows. In system 2, the hydrodynamics and heat-transfer phenomena of liquid droplets impacting upon a hot flat surface and particle are analyzed based on 3-D level-set method and IBM with consideration of the film-boiling behavior. The heat transfers in... 

Fig 1 Pressure Waves and Bubble Phenomena of Underwater Explosions. 

Flow in fluid beds Bubble phenomena Heat and mass transfer Axial dispersion... 

Bubble Separation Process Descriptions and Definitions Based on the Techniques Used for Bubble Generation Bubble Separation Process Descriptions and Definitions According to the Techniques Used for Solids Separation Bubble Separation Process Descriptions and Definitions According to the Operational Modes Surface Adsorption Bubble Phenomena Multiphase Flow Material Balances... 

Illustrations of velocity vectors for both kinds of these particles are illustrated in Figure 2. This concept has been useful in explaining many drop and bubble phenomena. For example, it has been found that trace amounts of surface-active materials can hinder the development of internal circulation by means of a differential surface pressure. Small bubbles rising slowly are apt to behave like particles with rigid surfaces. This phenomenon can lead to a decrease in k as the age of a bubble increases (Levich. 1956). Larger bubbles, rising more quickly, may sweep their front surface free of trace impurities and therefore escape... 

MiiUer CR, Davidson JP, Dennis JS, Petmell PS, Gladden LP Real time measurement of bubbling phenomena in a 3-D gas-fluidized bed using ultra-fast magnetic resonance imaging, Phys Rev Lett 96 154—504, 2006. 

The mass, momentum, and energy transport in the context of bubble phenomena in stagnant and/or moving liquids which exhibit complex rheological behavior is central to the understanding of the various applications. 

It is outside the scope of this chapter to cover the entire spectrum of bubble phenomena. Instead, we focus attention on the key issues dealing with the free-rise motion of bubbles in general and on the following aspects in particular ... 

Lee, S.L.P., H. de Lasa and M.A. Bergougnou. "Bubble Phenomena in Three-Phase Fluidized Beds as Viewed by a U-Shaped Fiber Optic Probe". Accepted for publication AIChE Symp. Series (1985). 

Davidson and Harrison [48] have studied bubbling phenomena in fluidized beds extensively and have shown that the rising velocity of gas bubbles in fluidized beds may be estimated with the aid of the Davies and Taylor equation, which was originally developed for the rise of large (spherical cap) gas bubbles in liquids ... 

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