Axial mixing of liquid in gas‐liquid flow through packed beds

Hoogendoorn, C. J.; Lips, J.

doi:10.1002/cjce.5450430306

Cited by 92 publications

(36 citation statements)

References 17 publications

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“…Dunn et al [21] found that axial mixing decreases with increasing liquid velocities, but no significant variation with the velocity of the gas was observed. The dependence on the gas velocity was hardly observed by Hoogendoorn and Lips [22] and Carleton et al [23]. In this work, the best agreement was found with the correlation of Otake and Kunugita…”

Section: Vsg Mlssupporting

confidence: 78%

Comparison of hydrodynamic parameters for countercurrent and cocurrent flow through packed beds

et al. 1997

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Hydrodynamic parameters have been determined in common equipment, i.e., same column and liquid and gas distributors, for cocurrent and countercurrent two-phase flow through fixed beds. The piston/dispersion exchange model (PDE) with usual Danckwerts' boundary conditions (closed/closed system) has been used to describe the liquid flow. A new imperfect pulse method has been used to estimate the PDE model parameters directly from the experimentally nonideal input and output response. The transition between trickle flow and pulse flow, for two-phase downflow, and the occurrence of flooding, for countercurrent flow, has been investigated using a macroscopic model for the two-phase flow.

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Section: Vsg Mlssupporting

confidence: 78%

Comparison of hydrodynamic parameters for countercurrent and cocurrent flow through packed beds

et al. 1997

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“…At first the experimental impulse response u(t) was calculated numerically from the input and the output signals on the basis of the following equation y'(t)= Xf'(t-X)u(lW (10) where /' (O and y' (t) represent the first derivatives of the input and the output signals, respectively. Then the parameters were estimated so as to minimize the following least-square error over a time range from Utote Error= 2M0-c,i(0}2 (1 1) The time range [tb, te], which is essentially arbitrary, is determined according to the previous work17) as h={ta+tc)i2 te=4(tc-ta)+ta (12) (13) where ta is the breakthrough time and tc is the peak time. In many cases of minimum-value problems of estimating the model parameters, it is considered that the objective function have a multimodal surface.…”

Section: Mathematical Model and Methods Of Data Analysismentioning

confidence: 99%

Axial dispersion of liquid in concurrent gas-liquid downflow in packed beds.

Matsuura

Akehata

Shirai

1976

J. Chem. Eng. Japan

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The axial dispersion in the liquid-phase of a gas-liquid down flow through a packed column was studied with air and water flowing concurrently in a 8.0 cm diameter column with glass spheres of 0.12, 0.26 and 0.43 cm.The impulse response was calculated numerically from the two signals measured at two crosssections in the bed. The response was characterized by both a peak and a very long tail, and could be represented satisfactorily by using the PDEmodel in which the mass transfer between the dynamic and the stagnant holdups in addition to the axial dispersion in the dynamic holdup was taken into account. Four parameters appearing in the PDEmodel were determined by means of the time domain curve fitting method. Peclet number which was based on the actual velocity in the dynamic holdup ud had a constant value of 0.43 for ReX=udpdvl» < 150, increased with Re' and attained another constant value of1.7 for Re >400.The volumetric mass transfer coefficient was correlated as a function of particle size, liquid and gas velocities. The total liquid holdup agreed well with the literature data. The fraction of the dynamic holdup varied in the range of 0.6 to 0.95 depending on the particle size and the gas and the liquid velocities. The correlation of the dynamic liquid holdup was given graphically.

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“…Since the ultimate application of dispersion data is usually to steady state systems, distinctions between steady and unsteady state situations must be accounted for. Single-parameter diffusion mechanisms are not generally adequate to characterize transient measurements, as has recently been observed (20). On the other hand, such mechanisms appear to be satisfactorily commensurate with steady state behavior.…”

Section: Discussion a N D Conclusionmentioning

confidence: 92%

The influence of axial dispersion on carbon dioxide absorption tower performance

Brittan

Woodburn

1966

AIChE Journal

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Carbon dioxide was absorbed from mixtures with nitrogen by countercurrent contact with water in an experimental packed tower. Radial and axial gas concentration profiles were determined from measurements made within the packing. Substantial gas phase channeling was observed. Characterizing the gos flow regime by both piston flow and axial diffusion models yielded mass transfer data and computed axial gas concentration profiles. Differences between the mass transfer results for the two models allowed the influence of axial dispersion to be assessed. Comparison of the piston flow and axially dispersed profiles with the experimental profiles enabled conclusions to be drawn regarding the applicability of the axial diffusion model and the accuracy of available dispersion parameter values.The axial diffusion model appears to be a satisfactory representation of the process. The dispersion coefficients used were found to be too high, which emphasizes shortcomings in the transient response experiments yielding dispersion coefficients. The influence of dispersion on the performance was found to be only moderately adverse. The effect increases with increasing liquid rate, decreasing gas rate, and decreasing packing height. It is improbable that the effect is large enough to account for the difference between industrial scale performance and that predicted from available mass transfer correlations.The spread of fluid element residence times prevailing in an absorption tower invalidates the piston flow assumption inherent in existing design techniques. The resulting longitudinal dispersion will, in some measure, have an adverse influence on the performanoe. The magnitude of this effect has not as yet been determined, however. For carbon dioxide absorbers, in particular, it has been speculated that the wide discrepancy between the actual industrial scale performance and that predicted from standard mass transfer correlations (19,28,31) is due to axial dispersion of the gas phase. In two-phase operation of this nature, substantial gas phase mixing will be induced by the countercurrent liquid flow, particularly at the high water rates necessary to achieve satisfactory absorption of relatively insoluble gases such as carbon dioxide. Published gas-side dispersion coefficients for twophase operation are scarce, but those available (11, 12) would indicate the effect of dispersion on the performance to be significant, especially if projected into the range of industrial liquid rates. The values of dispersion coefficients such as these, obtained from transient response experiments, have not been verified by application to steady state systems of practical interest. Consequently, their accuracy is subject to some question, and they cannot be employed to make definitive predictions.The study described in this paper presents data to indicate the degree to which axial dispersion will affect absorption tower performance. By using published dispersion coefficients, the investigation serves also as a test of their accuracy. The evidence upon...

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Axial mixing of liquid in gas‐liquid flow through packed beds

Cited by 92 publications

References 17 publications

Comparison of hydrodynamic parameters for countercurrent and cocurrent flow through packed beds

Comparison of hydrodynamic parameters for countercurrent and cocurrent flow through packed beds

Axial dispersion of liquid in concurrent gas-liquid downflow in packed beds.

The influence of axial dispersion on carbon dioxide absorption tower performance

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