Bubble Size in a Cocurrent Fiber Slurry

Abstract

Bubble diameter measurements in a two-dimensional cocurrent bubble column are obtained using a gas−liquid−solid system in which the solid component is a cellulose fiber. Flash X-ray radiography, a noninvasive measurement technique, is used to record bubble size in the opaque slurry at various operating conditions. Results are presented for a range of fiber mass fractions (0 ≤ C ≤ 1.5%), a range of superficial gas velocities (1 ≤ υg ≤ 4 cm/s), two superficial liquid velocities (υl = 1 or 2 cm/s), and two column heights (H = 15−40 or 115−140 cm). Bubbles are categorized as either large (dB > 10 mm) or small (dB ≤ 10 mm), and all bubble diameter distributions can be characterized by log-normal distributions. The presence of fibers has the most significant effect on the large bubble size and population, even at mass fractions as low as 0.5%. In general, the large bubble size and population increases with column height, superficial gas velocity, and fiber mass fraction. Bubble diameter measurements in a two-dimensional cocurrent bubble column are obtained using a gas-liquid-solid system in which the solid component is a cellulose fiber. Flash X-ray radiography, a noninvasive measurement technique, is used to record bubble size in the opaque slurry at various operating conditions. Results are presented for a range of fiber mass fractions (0 e C e 1.5%), a range of superficial gas velocities (1 e υ g e 4 cm/s), two superficial liquid velocities (υ l ) 1 or 2 cm/s), and two column heights (H ) 15-40 or 115-140 cm). Bubbles are categorized as either large (d B > 10 mm) or small (d B e 10 mm), and all bubble diameter distributions can be characterized by log-normal distributions. The presence of fibers has the most significant effect on the large bubble size and population, even at mass fractions as low as 0.5%. In general, the large bubble size and population increases with column height, superficial gas velocity, and fiber mass fraction. Disciplines Mechanical Engineering Comments Reprinted with permission from

Hydrodynamic drag and velocity of micro-bubbles in dilute paper machine suspensions

“…During their rise, bubbles have to push solids away from their path. In addition, fibres in model suspensions dampen the flow velocity fluctuations and resist the flow from becoming turbulent, as reported in [3,4,12]. In process waters, bubbles were seen to align in swarms more strongly than in pure gasliquid suspension.…”

“…Fibre content appears to have even higher impact on mean bubble size than changes in surface tension and viscosity. Although increased fibre consistency is also noted to promote large bubble formation [3,4], that trend is not visible here. Actually fewer micro-bubbles are generated in fibre suspensions than in pure liquids.…”

“…The rise of free gas bubbles in papermaking suspensions is hindered by apparent viscosity and solids, while surface tension of the liquid phase affects the size distribution of formed bubbles [3][4][5][6][7][8]. This is also typical for fibre-free filtration waters drained from sheet former, commonly referred as white waters.…”

Similitude Analysis for Gas-Liquid-Fiber Flows in Cocurrent Bubble Columns

“…The presence of fibers can make the effective rheological properties of a fiber suspension significantly different from those of the suspending fluid [64][65][66]. Fiber floes or networks can significantly affect bubble motion, coalescence, and breakup, and thus, gas holdup in the bubble column [2,5,11,12,20,[67][68][69]. Pelton and Piette [69] reported that the main reason bubbles are held up in a fiber suspension is mechanical confinement, not bubble adhesion to fibers.…”

“…Bubble size distribution in gas-liquid-fiber flows and its variation with fiber mass fraction and fiber type have been investigated in semi-batch [8-1 0] and cocurrent bubble columns [11 ]. Gas holdup in gas-liquid-fiber systems has also been studied in both semi-batch [2,[12][13][14][15][16][17][18] and co current [2,[19][20][21][22][23] bubble columns.…”