Impact of Internals on the Gas Holdup and Bubble Properties of a Bubble Column

Abstract

Most industrial applications involving bubble columns require the addition of internals for heat exchanging. However, most academic research on bubble columns has been performed in hollow (empty) ones. Hence, the impact of internals on the hydrodynamics of a bubble column has been insufficiently studied in the open literature. Accordingly, this study focuses on investigating the effect of internals that mimic those used in methanol synthesis (5% covered cross-sectional area) and the Fischer-Tropsch (FT) process (22% covered cross-sectional area) on the local gas holdup, gas-liquid interfacial area, bubble chord length, and bubble velocity distributions. The investigations have been performed using a four point optical probe in an 8 in. diameter column. An air-water system was used with superficial gas velocities up to 20 cm/s. An increase in gas holdup and interfacial area was obtained upon insertion of the internals, although the impact of the less dense internals (5% covered area) was not significant. However, in the case of dense internals, the bubble chord length decreased, yielding a decrease in the bubble velocity.

Hydrodynamics in bubble columns with pin-fin tube internals

“…As indicated in literature Youssef et al, 2012), the overall gas holdup increases with the increase of internal covered CSA and our results are consistent with these conclusions. Comparing with plain tube internals, pin-fin tube internals reduce the bubble size and increase the overall gas holdup because the pin fins increase the bubble break-up rate and decrease the bubble contact probability.…”

“…The gas holdup in the centre region increases with the increase of measured axial position, and it is implied that the gas-liquid flow lies in the distributor region and there is no well-developed region. The measured gas holdup profiles in bubble columns with plain tube internals were parabolic in the literature(Kagumba and Al-Dahhan, 2015;Youssef and Al-Dahhan, 2009;Youssef et al, 2012;Zhang et al, 2009), similar to cases in bubble columns without internals.The different phenomenon may come from different column sizes: the diameter of the bubble column in this paper is 0.8 m and it is much larger than the bubble columns in the literature(Kagumba and Al-Dahhan, 2015;Youssef and Al-Dahhan, 2009;Youssef et al, 2012;Zhang et al, 2009). The influence of column diameter on the flow development is detailedly discussed in the work(Guan et al, 2014b).…”

“…They observed that the presence of internals gave rise to decreases of liquid fluctuation velocity and radial dispersion, and an enhancement of large scale liquid circulation, but there were no experimental data presented in the work to reflect the influence of internals on the liquid velocity. Bubble dynamics in bubble columns with dense internals have been comprehensively investigated in some works Youssef et al, 2012). The 8 in.…”

Characterization of Bubble Size Distributions within a Bubble Column

“…This method is most common when the measurements are acquired with electrical impedance/resistivity [10][11][12], wire mesh [13][14][15] or optical [16] point probes, which can only provide a single length scale but a relatively large sample size. These measurements are sensitive to the bubble size, velocity, shape and orientation as well as the sensor design (e.g., response from optical/impedance probes are unique to the sensor design and fluid properties).…”

Mechanism on lateral distribution of small bubbles in vertical bubbly upflows

“…So far, a great number of numerical and experimental investigations show that the void fraction profile displays various distributing patterns depending on the flow conditions and environments, and through reviewing the existing references, it is discovered that the void fraction profile is tightly associated with numerous factors such as bubble size, global void fraction, bubble shape, flow direction with respect to gravity, bubble injection place, liquid velocity, gas velocity, pipe diameter, air injection method, gravity, purity of liquid, etc. [3][4][5][6][7][8][9][10][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Based on the results of the references (such as Serizawa et al [24], Nakoryakov et al [20], Liu [15], Okawa et al [21], etc.)…”