Characterization of Bubble Size Distributions within a Bubble Column

Abstract

Abstract:The current study experimentally examines bubble size distribution (BSD) within a bubble column and the associated characteristic length scales. Air was injected into a column of water via a single injection tube. The column diameter (63-102 mm), injection tube diameter (0.8-1.6 mm) and superficial gas velocity (1.4-55 mm/s) were varied. Large samples (up to 54,000 bubbles) of bubble sizes measured via 2D imaging were used to produce probability density functions (PDFs). The PDFs were used to identify an alternative length scale termed the most frequent bubble size (d mf ) and defined as the peak in the PDF. This length scale as well as the traditional Sauter mean diameter were used to assess the sensitivity of the BSD to gas injection rate, injector tube diameter, injection tube angle and column diameter. The d mf was relatively insensitive to most variation, which indicates these bubbles are produced by the turbulent wakes. In addition, the current work examines higher order statistics (standard deviation, skewness and kurtosis) and notes that there is evidence in support of using these statistics to quantify the influence of specific parameters on the flow-field as well as a potential indicator of regime transitions.

Study of Bubble Size, Void Fraction, and Mass Transport in a Bubble Column under High Amplitude Vibration

“…Sauter mean diameter (d 32 ) was measured from still images similar to other studies in the literature [18][19][20]24,27]. A series of images (>10) with an exposure of 250 µs were taken at each column height (h = 30, 45 and 60 cm) to quantify any height dependence.…”

“…The flow visualization setup used to produce both air-water interface and bubble images is shown in Figure 2. For more information on bubble measurement uncertainty using the current experimental setup, the interested reader is directed to Mohagheghian and Elbing [24]. …”

“…Filtered (5 µm) compressed air was injected near the base of the column through a 15 gauge, 316-stainless steel round tube with an inner diameter of 1.6 mm. For more information on the effect of injector tube size on bubble size distribution in the same test facility as presented in the current work the interested reader is directed to Mohagheghian and Elbing [24]. Based on past observations [33], it is expected that the injector tube diameter has a negligible effect on gas holdup and bubble size when the injector tube diameter is larger than 1-2 mm.…”

“…It is worth mentioning that unless stated, the bubble size measurement was conducted 6D downstream of the injector tube to eliminate any influence from the injection condition [24]. Prior to analyzing the mean statistics, the temporal evolution of the bubble size is examined to determine steady state conditions.…”

“…Therefore, bubble size classification is necessary to determine an average interfacial area [24]. Use of a single length scale would be appropriate for characterizing the bubble size if the bubble shape is readily represented with a single length scale (e.g., sphere) and the shape of the size distribution was constant [24]. Sauter mean diameter (d 32 ),…”