Heat Transfer and Hydrodynamics in a Three-Phase Slurry Bubble Column

Abstract

The instantaneous and time-averaged heat transfer coefficients in the regions near the wall and at the center and average gas holdups were measured in a 0.28 m diameter slurry bubble column for the air−water and air−water−glass beads (35 μm) system. The effects of high gas velocities (up to 0.35 m/s) and high solids concentrations (up to 40 vol %) were investigated. Gas holdup decreased with increasing slurry concentrations; the rate of decline was rapid at high gas velocities. The instantaneous local heat transfer measurements were analyzed to study the bubble behavior in the regions near the wall and at the center for different solids concentrations. Larger bubbles were detected in the wall region in slurry systems compared to the solid-free system. The average heat transfer coefficient decreased with increasing slurry concentrations. The heat transfer coefficient was always lower at the wall than at the center.

Characterization of Bubble Size Distributions within a Bubble Column

“…Viscosity plays a more complex role [23] as illustrated with reports of increasing [24] and decreasing [25] bubble size with increasing viscosity. However, fluid properties had minimal variation in the current work with filtered air injected into filtered water at nearly constant temperature.…”

“…Fluid properties are known to affect the size distribution with bubble size decreasing with increasing liquid density [21] and decreasing surface tension [22]. Viscosity plays a more complex role [23] as illustrated with reports of increasing [24] and decreasing [25] bubble size with increasing viscosity. However, fluid properties had minimal variation in the current work with filtered air injected into filtered water at nearly constant temperature.…”

Gas holdup in a gas-liquid-fiber semi-batch bubble column

“…Similar phenomena have been observed by Li and Prakash (1997). These observations indicated that the decrease in total gas holdup with increasing solid volume fraction resulted from the decrease in the dense phase gas holdup because solid addition reduced the small bubble population.…”

“…Gas holdup behavior in gas-liquid-solid (GLS) bubble columns, in which the solid material is spherical or irregular like glass beads, sand, or coal particles, has been extensively studied by various investigators (Kara et al, 1982;Kelkar et al, 1984;Koide et al, 1984;Banisi et al, 1995b;De Swart et al, 1996;Krishna et al, 1997;Li and Prakash, 1997;Gandhi et al, 1999). These studies show that the presence of a solid particle in a bubble column decreased gas holdup from that observed in simple gas-liquid (GL) systems.…”

“…These observations indicated that the decrease in total gas holdup with increasing solid volume fraction resulted from the decrease in the dense phase gas holdup because solid addition reduced the small bubble population. Li and Prakash (1997), Zahradnik et al (1997), and Gandhi et al (1999) attributed the decrease in gas holdup with increasing solid mass fraction to fine particles enhancing the bubble coalescence rate and/or reducing the bubble breakup rate because the apparent suspension viscosity was higher than that of a similar GL system. Banisi et al (1995b) also proposed two mechanisms for the decrease in gas holdup with solid addition: (i) an increase in the rise bubble velocity due to wake stabilization, leading to a decreased residence time and gas holdup, and (ii) a change in the radial gas holdup and flow profiles from nearly flat to parabolic with upward flow near the center and downward flow near the wall, reducing the average gas holdup.…”