Bubble behavior and void fraction fluctuation in vertical tube banks immersed in a gas–solid fluidized-bed model

Ozawa, Mamoru; Umekawa, Hisashi; Furui, Shuji; Hayashi, Kouichi; Takenaka, Nobuyuki

doi:10.1016/s0894-1777(02)00178-4

Cited by 15 publications

(12 citation statements)

References 15 publications

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“…7 (b) and (c)), higher void fraction is predicted along the tube, indicating rising bubbles in contact with the tubes. The trajectories of rising bubbles with and without vertical tubes are also measured by Ozawa et al [44], and are consistent with our simulation results. Similarly, the time-averaged gas velocity magnitude (Fig.…”

Section: Effect Of Vertical Tube Arrangementsupporting

confidence: 93%

“…Radial motion of particles is less pronounced for vertical tubes, preventing radial mixing. Authors [8,44] is seen near the bed walls due to more free space available due to the presence of only auxiliary tube of relatively small tube diameter (see Table 3). For the triangular tube arrangement data shown in Fig.…”

Section: Solids Flow Characteristicsmentioning

confidence: 99%

“…In the 7 presence of vertical tubes, bubbles are comparatively smaller and distributed throughout the bed. As 8 discussed in the literature[8,44], vertical tubes prevent coalescence and promote bubble splitting. This 9 phenomenon was observed in our simulation animations.Fig.…”

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confidence: 99%

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Hydrodynamics of gas–solids flow in a bubbling fluidized bed with immersed vertical U-tube banks

Verma

Dietiker

et al. 2016

Chemical Engineering Journal

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We apply a two-fluid model (TFM) from the open-source code Multiphase Flow with Interphase eXchanges (MFIX) to investigate hydrodynamics in a gas-solids fluidized bed with immersed vertical tubes. The cut-cell method implemented in MFIX is used to fully resolve the flow around vertical U-tube banks. Simulations are performed in a bed diameter of 0.145 m with square and triangular tube arrangements, for inlet gas velocities of U 0 /U mf = 2.3, 4.5 and 6.8. Simulation results are compared with experimental results from the literature and show very good agreement for the bubble size. The efficiency of vertical tubes in reducing bubble size depends upon inlet gas velocity and tube arrangement. Reduction in bubble size is due to the vertical tubes preventing bubble coalescence and promoting bubble splitting. In-bed vertical tubes result in uniform distribution of bubbles within the bed with increase in bubble frequency. The bubble frequency is higher within the bed for square tube arrangements. For a bed with vertical tubes, the bubble shape is generally elongated, which results in high bubble rise velocity. Axial solid velocity and solids circulation patterns are significantly affected by the vertical tubes, where triangular tube arrangements rarely show any solids circulating zone.

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Section: Effect Of Vertical Tube Arrangementsupporting

confidence: 93%

Section: Solids Flow Characteristicsmentioning

confidence: 99%

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Hydrodynamics of gas–solids flow in a bubbling fluidized bed with immersed vertical U-tube banks

Verma

Dietiker

et al. 2016

Chemical Engineering Journal

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“…19 In industrial fluidized beds, vertical internals, such as vertical rods, vertical tubes, vertical helix springs, etc., are typically used as heat exchangers. 4 Heat exchange with vertical tubes is slightly different from horizontal tubes, as explained in the work of Ozawa et al 20 A significant drawback of vertical tubes compared to freely bubbling fluidized beds is their reduction of axial and lateral solids mixing, such that particle segregation is promoted and proper fluidization becomes difficult due to "channeling". 2,5,19 In the literature, only limited research has been published on vertical tubes in fluidized bedsin particular at laboratory scale.…”

Section: ■ Introductionmentioning

confidence: 99%

Bubble Characterization in a Fluidized Bed with Vertical Tubes

Rüdisüli

Schildhauer

Biollaz

et al. 2012

Ind. Eng. Chem. Res.

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Vertical tubes are commonly used in industrial fluidized beds as heat exchanger tubes. In this study, the influence of vertical tube banks on the axial bubble growth in a 145-mm inner diameter (ID) fluidized bed with Geldart B particles is experimentally investigated by means of pressure fluctuation measurement (PFM) and optical probing (OP). The employed tube bank configurations differ in their tube-to-tube spacing, tube diameter, and tube arrangement (square versus triangular). PFM and OP show that immersed vertical tube banks, irrespective of their configuration, significantly reduce the axial bubble growth. The bubble size reduction is even more significant for higher gas velocities (u 0/u mf > 4.6, where u 0 is the superficial gas velocity and u mf is the minimum fluidization velocity) as well as if the tube-to-tube spacing is narrow and the tube diameter is small. The tube arrangement (square versus triangular), in turn, does not show any significant differences. Depending on the gas velocity, the ratio of the bubble diameter to the tube diameter and the tube-to-tube spacing is changed. This change invokes a different bubble flow pattern between the vertical tubes and different bubble growth mechanism, which defines the effectiveness of vertical tubes to delay slugging and makes the fluidization smoother.

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“…As pointed by Achim et al (2002), the factors can be classified as particle characteristics, mechanical design and operating conditions. Some previous experimental studies have focused on bubble and particle behaviors (Kobayashi et al, 2000, Ozawa et al, 2002, tube attrition, erosion or wastage (Bouillard and Lyczkowski, 1991;Lee and Wang, 1995;Fan et al, 1998;Wiman, 1994), heat transfer (Wong andSeville, 2006, Wiman andAlmstedt, 1997) and gas flow regimes (Wang et. al, 2002).…”

Section: Introductionmentioning

confidence: 99%