Deformations and Splittings of a Bubble in a Two-Dimensional Fluidized Bed

Abstract

The behavior of deformations and splittings of a single bubble was studied experimentally in a two-dimensional fluidized bed. It was found that small downward cusps were generated at the bubble surface near the stagnation point and that they grew and necessarily caused bubble deformations and, frequently, bubble splittings.The authors call these cusps "disturbances". The frequencies of disturbances and splittings were observed and the following results were found. 1) About 4~8 disturbances were generated per second almost near the stagnation point, and they ran along the edge of a bubble to be lost near the wake; 2) about 14~30 percent of the disturbances also caused bubble splittings;3) there were two types of splittings; 4) the frequencies of distrubances and splittings decreased with increase of particle diameter; and 5) neither frequency depended much on bubble diameter.

A generalized bubble diameter correlation for gas‐solid fluidized beds

“…The frequency of bubble splitting does not depend upon bubble diameter but does depend upon particle diameter. Toei et al (1974a) data show thatf: is proportional to d;o.6 or possibly to d;'.'. Tone et al (1974) reported that bubble diameter decreases with increasing temperature.…”

“…On the mechanism of bubble breakup, they found that it is initiated mostly from bubble roof, not from the wake as was expected by Davidson and Harrison (1963), and pointed out that the case should be treated as a Taylor instability problem. Toei et al (1974a) made a quantitative measurement of bubble splitting in a two-dimensional bed and found that the bubble splitting frequency does not depend on bubble diameter but does depend on the particle size. Their results are shown in Figures 1 and 2.…”

“…In constrast to the bubble coalescence problem, which is purely a hydrodynamic problem and has been solved completely (Toei et al, 1967;Clift and Grace 1971), the theory for the bubble splitting problem has been developed rather slowly because it requires much fundamental analysis of the properties of emulsion phase itself. Thus, as far as the authors' knowledge is concerned only the work by Toei et al (1974a) gives quantitative data for bubble splitting frequency. Werther (1983) presented a bubble diameter formula for fine powders, introducing a critical height above which no bubble growth takes place, but no correlation has yet been proposed for it.…”

Tennessee Valley Authority atmospheric fluidized-bed combustor simulation interim annual report, January 1-December 31, 1979

“…Hence, the maximum stable diameter would depend on the terminal velocity of the bed material and therefore on the particle size, shape factor, and physical properties of the bed material. Data presented by Rowe and Partridge (1965) and by others Toei et al 1974) have raised questions about the validity of this criterion.…”

Fluidized-Bed Reactors

“…18) describes not only bubble growth by coalescence but also the splitting of bubbles (second term on the righthand side [49]). The crucial parameter here is the mean bubble lifetime λ:…”