Measurement techniques for local and global fluid dynamic quantities in two and three phase systems

Kumar, Dilip; Dudukovic,; Toseland, Christopher P.

doi:10.1016/b978-044482521-6/50002-4

Cited by 16 publications

(7 citation statements)

References 63 publications

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“…Equation (1) accounts for the effects of wall shear stress but neglects the effect of liquid acceleration due to void changes that may influence gas holdup in cocurrent bubble columns [14][15][16]; however, these effects were estimated to be negligible for the conditions of this study. The overall column gas holdup is defined as e = (&1 + &2 + &3) / 3, the average gas holdup in the three lower sections.…”

Section: Methodsmentioning

confidence: 99%

Gas Holdup in a Cocurrent Air-Water-Fiber Bubble Column

Tang

Heindel

2004

Volume 3

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Effects of superficial liquid velocity (Ul ), superficial gas velocity (Ug ), and fiber mass fraction (C) on gas holdup (ε) and flow regime transition are studied experimentally in well-mixed water-cellulose fiber suspensions in a cocurrent bubble column. Experimental results show that the gas holdup decreases with increasing Ul when C and Ug are constant. The gas holdup is not significantly affected by C in the range of C < 0.4%, but decreases with increasing C in the range of 0.4% ≤ C ≤ 1.5%. When C > 1.5%, a significant amount of gas is trapped in the fiber network and recirculates with the water-fiber slurry in the system; as a result, the measured gas holdup is higher than that at C = 1.5%. The axial gas holdup distribution is shown to be a complex function of superficial gas and liquid velocities and fiber mass fraction. The drift-flux model is used to analyze the flow regime transitions at different conditions. Three distinct flow regimes are observed when C ≤ 0.4%, but only two are identified when 0.6% ≤ C ≤ 1.5%. The superficial gas velocities at which flow transition occurs from one regime to another are not significantly affected by Ul and slightly decrease with increasing C. ABSTRACTEffects of superficial liquid velocity (U/), superficial gas velocity (U g ), and fiber mass fraction (C) on gas holdup (c) and flowregime transition are studied experimentally in well-mixed water-cellulose fiber suspensions in a cocurrent bubble column. Experimental results show that the gas holdup decreases with increasingU/ when C and U g are constant. The gas holdup is notsignificantly affected by C in the range of C < 0.4%, but decreases with increasing C in the range of 0.4%~C ::; 1.5%.WhenC > 1.5%, a significant amount of gas is trapped in the fibernetwork and recirculates with the water-fiber slurry in the system; as a result, the measured gas holdup is higher than that atC::: 1.5%. The axial gas holdup distribution is shown to be a complexfunction of superficial gas and liquid velocities and fibermass fraction. The drift-flux model is used to analyze the flowregime transitions at different conditions. Three distinct flowregimes are observed when C~0.4%, but only two are identifiedwhen 0.6% s C s 1.5%. The superficial gas velocitiesat which flow transition occurs from one regime to another are not significantly affected by U/ and slightly decreasewith increasing C. KEYWORDS:Bubble column; Cellulose fiber; Gas holdup; Hydrodynamics;Multiphase flow NOMENCLATUREBo coefficient in Eq. (3), Eo = COUI +U 1m C fiber mass fraction

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Section: Methodsmentioning

confidence: 99%

Gas Holdup in a Cocurrent Air-Water-Fiber Bubble Column

Tang

Heindel

2004

Volume 3

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“…[3][4][5] Using photographic techniques, Lin et al 6 showed that bubble size in a gas-liquid system decreases with increasing pressure. Photographic methods were also used by Glasgow et al 7 to measure bubble diameter in an airlift fermentor.…”

Section: Introductionmentioning

confidence: 99%

Bubble Size in a Cocurrent Fiber Slurry

Heindel

2002

Ind. Eng. Chem. Res.

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Bubble diameter measurements in a two-dimensional cocurrent bubble column are obtained using a gas−liquid−solid system in which the solid component is a cellulose fiber. Flash X-ray radiography, a noninvasive measurement technique, is used to record bubble size in the opaque slurry at various operating conditions. Results are presented for a range of fiber mass fractions (0 ≤ C ≤ 1.5%), a range of superficial gas velocities (1 ≤ υg ≤ 4 cm/s), two superficial liquid velocities (υl = 1 or 2 cm/s), and two column heights (H = 15−40 or 115−140 cm). Bubbles are categorized as either large (dB > 10 mm) or small (dB ≤ 10 mm), and all bubble diameter distributions can be characterized by log-normal distributions. The presence of fibers has the most significant effect on the large bubble size and population, even at mass fractions as low as 0.5%. In general, the large bubble size and population increases with column height, superficial gas velocity, and fiber mass fraction. Bubble diameter measurements in a two-dimensional cocurrent bubble column are obtained using a gas-liquid-solid system in which the solid component is a cellulose fiber. Flash X-ray radiography, a noninvasive measurement technique, is used to record bubble size in the opaque slurry at various operating conditions. Results are presented for a range of fiber mass fractions (0 e C e 1.5%), a range of superficial gas velocities (1 e υ g e 4 cm/s), two superficial liquid velocities (υ l ) 1 or 2 cm/s), and two column heights (H ) 15-40 or 115-140 cm). Bubbles are categorized as either large (d B > 10 mm) or small (d B e 10 mm), and all bubble diameter distributions can be characterized by log-normal distributions. The presence of fibers has the most significant effect on the large bubble size and population, even at mass fractions as low as 0.5%. In general, the large bubble size and population increases with column height, superficial gas velocity, and fiber mass fraction. Disciplines Mechanical Engineering Comments Reprinted with permission from

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“…In the present system taking into consideration of two phase medium, i.e. air and sand; the attenuation coefficient at different measurement conditions can be found out and similar equation as Eq (3) can be derived for each condition [10,11]. After solving a series of equations, Eq (4) is generated and is used to find out gas holdup fraction or voidage (e 2 ) in a fluidized bed.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

Measurement of mixing time and holdup of solids in gas–solid fluidized bed using radiotracer technique

Goswami

Biswal

Samantray

et al. 2014

J Radioanal Nucl Chem

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Mixing times and holdup of solids were measured in a gas-solid fluidized bed using radiotracer technique. Sand and air were used as solid and gas phase, respectively in the fluidized bed. Gold-198 labeled sand particles were used as radiotracer for mixing time measurement at different operating conditions and 137 Cs sealed source was used for holdup measurement at different axial and radial positions. The experiments were conducted at different operating conditions. The measured mixing times ranged from 1.4 to 21 s at different conditions. It was observed that at a particular bed height, the mixing time initially decreases with increasing gas velocity and tend to become constant at higher gas velocities. However, mixing time increases with increasing bed height. The holdup fraction of solid was found to be more towards the wall compared to the centre of the column. The study provided inputs to improve the existing design, design of a new system and scale-up of the process.

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Measurement techniques for local and global fluid dynamic quantities in two and three phase systems

Cited by 16 publications

References 63 publications

Gas Holdup in a Cocurrent Air-Water-Fiber Bubble Column

Gas Holdup in a Cocurrent Air-Water-Fiber Bubble Column

Bubble Size in a Cocurrent Fiber Slurry

Measurement of mixing time and holdup of solids in gas–solid fluidized bed using radiotracer technique

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