Impacting Bubbles

The preceding upper limit to particle size can be exceeded if more than one bubble is attached to the particle, t A matter relating to this and to the barrier that exists for a bubble to attach itself to a particle is discussed by Leja and Poling [63] see also Refs. 64 and 65. The attachment of a bubble to a surface may be divided into steps, as illustrated in Figs. XIII-8a-c, in which the bubble is first distorted, then allowed to adhere to the surface. Step 1, the distortion step, is not actually unrealistic, as a bubble impacting a surface does distort, and only after the liquid film between it and the surface has sufficiently thinned does... 

You ean see, ba.sed on the veloeity head formula, a eavitation bubble impacts the impeller and other pump parts at about 155,069 psi. Other experiments in test laboratories using a more preeise rHv, have calculated the impact pressure at 1 Gigapascal, or 147,000 psi. This is the reason that the damage from eavitation appears like someone was beating on your impeller with a large ball pein hammer. 

Film is locally removed by dissolution, surface shear stress or particle/bubble impact but it can repassivate. Erosion corrosion rate is a function of the frequency of film removal, bare metal dissolution rate and subsequent repassivation rate. 

Impacting bubbles. When bubbles collapse that are in contact with or very close to a solid surface, they collapse asymmetrically. Consider a spherical bubble impacting a... 

In a pioneering investigation, Serizawa [127, 128] measured the lateral void distribution as well as the turbulent axial liquid velocity fluctuations for bubbly air/water up-flows in a vertical pipe of diameter 60 (mm) inner diameter. They used electrical resistivity probes to measure the local void fraction, the bubble impaction rate, the bubble velocity and its spectrum. Turbulence quantities, such as the liquid phase mean velocity, and the axial turbulent fluctuations were measured using a hotfilm anemometer. A supplementary... 

Doubliez L (1991) The drainage and rupture of a non-foaming liquid film formed upon bubble impact with a free surface. Int J Multiphase Flow... 

The influence of surface location and orientation on the bed-to-surface heat transfer coefficient in circulating fluidized bed combustors is summarized in Table 13.6. The geometric construction of the combustor and the heat transfer surface is shown in Fig. 13.17. Besides the location and orientation, differences in local heat transfer can also be found on the heat transfer surface/tube. For example, the upper part of the horizontal tube shows the smallest value for the heat transfer coefficient in dense-phase fluidized beds due to less frequent bubble impacts and the presence of relatively low-velocity particles. 

When bubbles collapse that are in contact with or very close to a solid surface, they collapse asymmetrically. When a spherical bubble impacts a plane solid surface, the bubble becomes elongated with a tail and collapses. The jet from the bubbles can cause cavitation erosion on a solid wall (64). The implosion of a vapor bubble creates a microjet of liquid or microscopic torpedo of water that is ejected from the collapsing bubbles at velocities ranging from 100 m to 500 m/s. When the torpedo... 

In this article we refer to an actuator as closed when the associated chamber or channel volume is minimized, and as open when that volume is maximized. The volume in the closed position is called the dead volume, and the difference between the volume in the open position and the dead volume is the stroke volume. The stroke volume divided hy the dead volume is the compression ratio. Compression ratio is particularly important when purrping gases, since the amount of gas ejected from the actuator is reduced hy the compressihility of the fluid. In pure liquids this effect is much less, hut compression ratio plays an important role in determining how severely bubbles impact a particular purrp. In classifying micro-pumps, a distinction is sometimes made between integrated actuators - fabricated along with the other components of the microfluidic system - and external actuators - fabricated separately and attached later. It is common to see peristaltic micropumps of either kind. 

Figure 6-9. Bubble impact on the pipe surface within the mixing zone of the slug.

By constructing the bubble impact surface and bubble guide tube from a phenolic material, no metal parts are located in the immediate vicinity of the collapsing bubble to distort or give an erroneous reading of the local magnetic field generated. 

Once the bubble collapsed against this local impact area, it was permitted to escape from the phenolic guide tube outward through a bubble escape area between the bubble impact surface and the bubble guide tube and magnetic and electrostatic shield. 

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