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Title: Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

Abstract

Micro-bubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a down-flow bubble column reactor with micro-bubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fraction and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal measurements are discussed and compared for a bubble column reactor with dispersed micro-bubbles. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1,000 to 4,500 m 2/m 3) with sub-millimeter bubbles (500 to 900 µm) and high overall void fractions (10% – 60%)more » in comparison with previous bubble column reactor designs. The void fraction data was analyzed using slip velocity model and empirical correlation has been proposed to predict the Sauter mean bubble diameter.« less

Authors:
 [1];  [1];  [1];  [1];  [2];  [1]
  1. City College of New York, NY (United States)
  2. Homi Bhabha National Inst., Mumbai (India)
Publication Date:
Research Org.:
City College of New York, NY (United States)
Sponsoring Org.:
USDOE Advanced Research Projects Agency - Energy (ARPA-E); USNRC
OSTI Identifier:
1368176
Grant/Contract Number:
AR0000438; NRC-27-10-1120; NRC-HQ-12-G-38-0
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemical Engineering Science
Additional Journal Information:
Journal Volume: 168; Journal Issue: C; Journal ID: ISSN 0009-2509
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; Bubble column reactor; Microbubbles; Gamma-ray densitometry; High speed video photography; Void fraction profiles

Citation Formats

Hernandez-Alvarado, Freddy, Kalaga, Dinesh V., Turney, Damon, Banerjee, Sanjoy, Joshi, Jyeshtharaj B., and Kawaji, Masahiro. Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion. United States: N. p., 2017. Web. doi:10.1016/j.ces.2017.05.006.
Hernandez-Alvarado, Freddy, Kalaga, Dinesh V., Turney, Damon, Banerjee, Sanjoy, Joshi, Jyeshtharaj B., & Kawaji, Masahiro. Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion. United States. doi:10.1016/j.ces.2017.05.006.
Hernandez-Alvarado, Freddy, Kalaga, Dinesh V., Turney, Damon, Banerjee, Sanjoy, Joshi, Jyeshtharaj B., and Kawaji, Masahiro. 2017. "Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion". United States. doi:10.1016/j.ces.2017.05.006.
@article{osti_1368176,
title = {Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion},
author = {Hernandez-Alvarado, Freddy and Kalaga, Dinesh V. and Turney, Damon and Banerjee, Sanjoy and Joshi, Jyeshtharaj B. and Kawaji, Masahiro},
abstractNote = {Micro-bubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a down-flow bubble column reactor with micro-bubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fraction and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal measurements are discussed and compared for a bubble column reactor with dispersed micro-bubbles. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1,000 to 4,500 m2/m3) with sub-millimeter bubbles (500 to 900 µm) and high overall void fractions (10% – 60%) in comparison with previous bubble column reactor designs. The void fraction data was analyzed using slip velocity model and empirical correlation has been proposed to predict the Sauter mean bubble diameter.},
doi = {10.1016/j.ces.2017.05.006},
journal = {Chemical Engineering Science},
number = C,
volume = 168,
place = {United States},
year = 2017,
month = 5
}

Journal Article:
Free Publicly Available Full Text
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  • The influence of pressure, liquid viscosity, and gas velocity on the gas holdup and specific gas-liquid interfacial area in a bubble column reactor has been studied. The 18.7 L reactor had an inner diameter of 15.6 cm with a dispersion height set equal to 3 times the diameter and was operated at pressures between 0.1 and 6.6 MPa. By means of the chemically enhanced absorption of CO{sub 2} in diethanolamine, the gas-liquid interfacial area in the reactor has been determined. The viscosity has been changed in the range from 1 to 9.4 MPa{center_dot}s by adding ethylene glycol to the mixture.more » It is determined that pressure has a small effect on the gas holdup in pure water, whereas it shows a pronounced effect for the more viscous liquids. This can be attributed to the influence of the increased pressure on the flow regime transition. For the most viscous liquid all interfacial area data were obtained in the fully heterogeneous regime. Here the interfacial area increased with increasing pressure and was moderately affected by the gas velocity. For the less viscous liquids both pressure and gas velocity affect the interfacial area; this influence depends on the flow regime. Therefore, the state of the flow regime has an important impact on the mode in which the operating parameters affect the interfacial area.« less
  • Experiments were performed in atmospheric vertical air-water flows, for void fractions between 0.25 and 0.75 (cross-sectional averages) and superficial liquid velocities of 1.3, 1.7 and 2.1 m/s. Local values of void fraction and bubble velocity as well as the bubble diameter were measure by means of a resistivity probe technique. Reliable values were obtained for the local void fraction over the entire range 0 less than or equal to less than or equal to 1. The void fraction profiles appeared to have a local maximum at the pipe center, local maxima close to the wall were obviously absent. The resistivitymore » probes are shown to measure the velocity of the interface between the conducting and nonconducting phases, which equal the gas velocity only for low void fractions. The measured data for void fraction and bubble velocity were correlated by means of power law distribution functions, with exponents given by a function o the cross-sectionally averaged void fraction. The Sauter mean diameters for the bubble size spectr found, agree reasonably well with diameters predicted by a theoretical model based on the energy dissipation in the flow.« less
  • Subcooled flow boiling is encountered in many applications: nuclear reactors, boilers, refrigeration systems, and heat exchangers. The effect of bubble size on void fraction distribution in subcooled flow boiling in a vertical annular channel at low pressure is studied numerically. It is found that a simple linear formula used by Anglart and Nylund and adopted for calculation of bubble size as a function of local subcooling lacks a physical and experimental basis limiting the general application of the model for predicting subcooled flow boiling. A bubble size correlation proposed by Zeitoun and Shoukri has been employed in this study. Themore » predictions of void fraction profiles and the bubble size distributions, after incorporating the above bubble size correction, show very good agreement with the experimental data.« less
  • Influences of suspended particles upon such parameters as gas holdup, volumetric liquid-state mass-transfer coefficient, and gas-liquid interfacial area in a bubble column were investigated in sodium sulfite/sulfate solutions in which various loadings of coarse nylon particles and fine alumina particles were suspended. The volumetric mass-transfer coefficients and gas holdups were a bit increased by suspending a small amount of fine particles. The gas-liquid interfacial area in a slurry bubble column in which a small amount of fine particles were suspended was found to be higher than that in a two-phase bubble column.