Heat transfer and gas holdup studies in a bubble column: Air‐water‐sand system

Saxena, S.C.; Rao, N. V. Subba; Saxena, Aditi

doi:10.1002/cjce.5450700106

Cited by 24 publications

(16 citation statements)

References 23 publications

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“…This can be attributed to low mixing in the wall region and a higher local slurry concentration. Heat transfer in the slurry bubble columns has been investigated by several researchers (Deckwer et al, 1980;Saxena et al, 1989Saxena et al, , 1990Saxena et al, , 1992. Generally a weak dependence of the heat transfer coefficient on the slurry concentration has been observed.…”

Section: Heat Transfer Measurementmentioning

confidence: 99%

“…The effect of solids concentration on gas holdup has been attributed to an increase in the apparent viscosity of suspension due to the addition of particles (Kara et al, 1982;Fan 1989). Heat transfer studies in three-phase gas suspension reactors have been investigated by several researchers (Baker et al, 1978;Kato et al, 1981;Chiu and Ziegler, 1983;Saxena et al, 1990Saxena et al, , 1992. While most studies have focused on the measurements of time-averaged heat transfer, Kumar et al (1992) investigated instantaneous heat transfer coefficients in a bubble column.…”

Section: Introductionmentioning

confidence: 99%

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

Prakash

1997

Ind. Eng. Chem. Res.

102

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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.

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Section: Heat Transfer Measurementmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Prakash

1997

Ind. Eng. Chem. Res.

102

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“…Note that from the single liquid flow data a critical value of the dimensionless quantity E 1/3 D 4/3 /n l , dividing the turbulent and laminar regions, can be defined as about 160. The data for the heat transfer coefficient in the slurry bubble column without slurry flow by Saxena et al, (1991Saxena et al, ( , 1992 are plotted in the figure. The data for the air-water-sand system, indicated as slurry bubble column 1, lay close to our correlation line.…”

Section: Results Of Correlationmentioning

confidence: 99%

“…Their experimental data were characterized by a high Prandtl number for the high viscous liquid medium. Saxena et al (1992) measured the heat transfer coefficient in a slurry bubble column of an air-water-sand system using a tube bundle heating device. They proposed an empirical equation by modifying Deckwer's correlation (Deckwer, 1980).…”

Section: Department Of Chemical Engineering Kansai University 3-3-3mentioning

confidence: 99%

Vertical Cylinder‐to‐Slurry Heat Transfer in a Gas‐Slurry Transport Bed

et al. 2003

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She gas-slurry transport bed is a unique operation where the upward flow of a liquid-solid suspension is contacted with the concurrent up-flow of a reacting gas. Such an operation is exemplified by the main reactor and the preheater in a coal liquefaction process (Onozaki et al., 2000). The chemical absorption associated with reactant or product solids suspension for environmental protection use, the UASB unaerobic process using a suspended granular bed of self-coagulated microorganisms for treating wastewater from a food processing factory and the suspension electrolysis of metals are other industrial applications of the gas-slurry transport bed operation (e.g., Fan, 1989;Deckwer, 1992). The heat and mass transfer characteristics in the gas-slurry transport bed are important parameter in designing such a reactor.In the gas-liquid-solid fluidized beds where rather coarser particles are suspended in an expanded stationary bed, the wall-to-bed heat transfer coefficients were measured and correlated by several investigators (Muroyama et al., 2001b). So far several generalized correlation methods have been proposed for the heat and mass transfer coefficients in the gas-liquid-solid fluidized bed. Kato et al. (1981) measured the wall heat transfer coefficient using a short wall heater and correlated the data using a dimensionless empirical correlation. A similar approach was also employed by Kato et al. (1984a,b) and Kang et al. (1985) for correlating the immersed cylinder-to-bed heat transfer data in the three-phase fluidized bed. Muroyama et al. (1986a, b) employed the so called Colburn j-factor approach, that measured the apparent wall heat transfer coefficient excluding the effect of the interior radial heat transfer resistance and correlated the heat transfer coefficient in terms of the modified j-factor and the modified Reynolds number, correcting for the effect of bed expansion on the effective liquid velocity and the spatial arrangement of the particles. Meanwhile, Yasunishi et al. (1988) measured and correlated the wall-to-liquid mass transfer coefficient in the three-phase fluidized beds using the limiting current method. They correlated the mass transfer coefficient in a unified dimensionless formula in terms of the Sherwood number, the Schmidt number and the specific power group including the energy dissipation rate per unit mass of liquid. They indicated the presence of an analogy between the wall-to-liquid mass transfer and heat transfer in the three-phase fluidized bed. Muroyama et al. (2001a) measured the cylinder surface-to-liquid mass transfer coefficients for the vertically and horizontally arranged electrodes using the limiting current method and correlated the data in the same way as employed by Yasunishi et al. (1988). Muroyama et al. (2001b) In the present study we measured the immersed vertical cylinder surface-to-slurry heat transfer coefficient in the liquid-solid and gas-slurry (three-phase) transport beds at controlled solid concentrations. The slurry contained 0.1 mm inert glass beads...

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“…The influence of additional geometric parameters relevant to shallow columns has not been studied extensively. The heat transfer coefficient has been shown to vary with radial [13] and vertical [16,13] position in a tall column, and with vertical position in a short column [15]. Narayan et al [1] proposed that horizontal position of internals with respect to the gas sparger orifices could affect heat transfer coefficients.…”

Section: Introductionmentioning

confidence: 99%

Heat transfer to a horizontal cylinder in a shallow bubble column

Tow¹,

Lienhard²

2014

International Journal of Heat and Mass Transfer

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Heat transfer coefficient correlations for tall bubble columns are unable to predict heat transfer in shallow bubble columns, which have unique geometry and fluid dynamics. In this work, the heat transfer coefficient is measured on the surface of a horizontal cylinder immersed in a shallow air-water bubble column. Superficial velocity, liquid depth, and cylinder height and horizontal position with respect to the sparger orifices are varied. The heat transfer coefficient is found to increase with height until reaching a critical height, and a dimensionless, semi-theoretical correlation is developed that incorporates superficial velocity, liquid properties, and height. Additionally, the more minor effects of flow regime, column region, and bubble impact are discussed with the aim of informing design. Notably, the heat transfer coefficient can be as high in the region of bubble coalescence as in the bulk of the column, but only if the probe is placed so that bubbles impact the cylinder. The correlation and discussion provide a framework for modeling and designing * Address all correspondence to lienhard@mit.edu Greek

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Heat transfer and gas holdup studies in a bubble column: Air‐water‐sand system

Cited by 24 publications

References 23 publications

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

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

Vertical Cylinder‐to‐Slurry Heat Transfer in a Gas‐Slurry Transport Bed

Heat transfer to a horizontal cylinder in a shallow bubble column

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