Hydrodynamic analysis of dilute gas—solids flow in a vertical pipe

Arastoopour, Hamid; Pakdel, Parto; Adewumi, Michael A.

doi:10.1016/0032-5910(90)80080-i

Cited by 82 publications

(57 citation statements)

References 16 publications

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“…Bed volume also expands gradually by increasing airflow velocity until large heavy agglomerates start to move and a transition regime from the channeling regime to full fluidization regime is reached in the bed. 2,3,31,55,56,59 However, large agglomerates of the particle phase are observed in certain cases at the bottom of the conical bed. It should be noted that the fluidization of fine particles and/or large agglomerates is delayed and even completely stopped due to the presence of interparticle cohesive forces and/or weight.…”

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confidence: 96%

“…Moreover, a grid-sensitivity analysis has been carried out using uniform and near-wall refinement schemes to ensure that numerical results are close to the experimental data. The drag models suggested by Syamlal and O'Brien,51 Ahmadi and Ma, [52][53][54] Arastoopour et al, 55 and Gidaspow 56 have been used in the simulation and their suitability has been examined. …”

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confidence: 99%

“…The gas-solid momentum exchange coefficient is assumed to include only the drag contribution. Four different drag models are used here, which are those proposed by Syamlal and O'Brien, 51 Ahmadi and Ma, [52][53][54] Arastoopour et al, 55 and Gidaspow 56 (Appendix C). …”

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Effect of slip boundary conditions on the simulation of microparticle velocity fields in a conical fluidized bed

2013

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The hydrodynamic performance of micrometric TiO 2 particles has been experimentally studied in a conical fluidized bed and the results compared with numerical simulations. Local solid velocities in the bed have been measured by means of an optical fiber technique under different operating conditions of particle loading and air velocity. The radial profiles of axial solid velocities have been simulated to assess the sensitivity of grid size, and different drag models, namely, those by Syamlal and O'Brien, Ahmadi and Ma, Arastoopour et al., and Gidaspow, for no-slip, partial-slip, and free-slip boundary conditions (BCs). The different drag models record almost similar results, but those provided by the Gidaspow and Ahmadi-Ma models, together with free-slip BCs, are in somewhat better agreement with the experimental data for conical fluidized beds with smooth walls. V C 2013 American Institute of Chemical Engineers AIChE J, 59: [4502][4503][4504][4505][4506][4507][4508][4509][4510][4511][4512][4513][4514][4515][4516][4517][4518] 2013 Keywords: conical fluidized bed, solid velocity, slip boundary conditions, numerical simulation, drag models IntroductionFluidized and spouted beds are extensively used for various industrial applications in pharmaceuticals, 1,2 drying, 3,4 food processing, 5 combustion, 6,7 pyrolysis, and catalytic polymerization. 8,9 A conical fluidized bed has the characteristics of both fluidized and spouted beds, being, therefore, suitable for handling agglomerating or sticky powders. This is particularly the case for the fluidization of fine particles with a wide size distribution corresponding to different groups of Geldart's classification. 10,11 Although many studies have been reported in the literature involving fluidized beds, [12][13][14][15] certain details of the hydrodynamic performance of conical fluidized beds are not fully understood, which is partially due to the few experimental data on the hydrodynamics of these beds. 16,17 Accordingly, the design and scaling-up of conical fluidized beds is not straightforward, given that bed geometry, the ratio of inlet diameter to bed height and operating conditions highly influence gas-solid flow regime. Furthermore, hydrodynamic parameters such as pressure drop, solid volume fraction, and velocity significantly affect the performance of the conical bed. Optimizing the performance of conical fluidized beds requires a thorough understanding of the mixing characteristics and interactions between the gas and solid phases. The standard noninvasive measurement techniques used for the determination of particle trajectories and velocities are as follows: pitot tube, 18 Laser-Doppler anemometry, 19 video technique, 20 radioactive particle tracking, 21 and particle image velocimetry. 22 Nevertheless, techniques based on an optical-fiber probe are also promising for this purpose. [23][24][25][26][27][28][29] In recent years, with the development of high performance computers, researchers have used numerical methods to study the flow behavior of fluidized...

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Effect of slip boundary conditions on the simulation of microparticle velocity fields in a conical fluidized bed

2013

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“…The gas-solid interphase exchange coefficient, K gs , was modelled using the Arastoopour et al (1990), Di Felice (1994, Gidaspow et al (1992), modified drag correlation of (Benyahia et al, 2006) and the Syamlal and O'Brien (1987) drag models shown in Table 1. The different drag coefficients, C D , are given in Table 2.…”

Section: Conservation Of Momentummentioning

confidence: 99%

“…The Gidaspow model is a combination of the Wen and Yu (1966) model for dilute phases and the Ergun (1952) model for dense phases whereas the Syamlal-O'Brien model was developed on the basis of measurement of the terminal velocities of particles in fluidised beds. Other drag models include those of Arastoopour et al (1990) andDi Felice (1994). Although these models have performed reasonably, they are classified as empirical models because they were derived from the analysis of experimental data.…”

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The influence of multiple tubes on the tube-to-bed heat transfer in a fluidised bed

Armstrong

Luo

2010

International Journal of Multiphase Flow

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a b s t r a c tThere have been few studies modelling both flow and heat transfer in fluidised beds. The kinetic theory of granular flow (KTGF) has been used for flow prediction in the past without heat transfer modelling. In the present study, a two-fluid Eulerian-Eulerian formulation incorporating the KTGF was applied first to a tube-to-bed reactor with one immersed tube and compared with the results in the literature. The bed was then modified to introduce two and three heated tubes. The effects on the flow and temperature distribution, local heat transfer coefficients and averaged heat transfer coefficients over a 3.0 s time period were carried out. Results showed that increasing the number of tubes promotes heat transfer from tubes to the particles and flow. The heat transfer coefficients extracted from the single-tube to three-tube cases were analysed in detail, confirming the importance of linking flow/particle and heat transfer calculations.

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Fluidization of micronic particles in a conical fluidized bed: Experimental and numerical study of static bed height effect

Bahramian¹,

Olazar²

2011

AIChE Journal

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in Wiley Online Library (wileyonlinelibrary.com).The numerical simulations and experimental data of bed hydrodynamics in a conical fluidized bed unit are compared. Experimental studies have been carried out in a bed containing TiO 2 particles belonging to A/C boundary of Geldart's classification with a wide particle-size distribution. Thus, pressure measurements and an optical fiber technique allowed determining the effect of static bed height on the fluidization characteristics of micronic particles. Numerical simulations have then been performed to evaluate the sensitivity of gas-solids drag models. The Eulerian multiphase model has been used with different drag models and three boundary conditions (BC) consisting of noslip, partial-slip, and free-slip. The numerical predictions using the Gidaspow drag model and partial-slip BC agreed reasonably well with the experimental bed pressure drop measurements. The simulation results obtained for bed expansion ratio show that the Gidaspow model with the free-slip BC best fit with the experimental data. V V C 2011 American Institute of Chemical Engineers AIChE J, 58: 730-744, 2012 Keywords: fluidization, hydrodynamics, CFD simulation, conical fluidized bed, drag models, boundary conditions Introduction Fluidization in conical vessels is a useful technique with a variety of applications in drying, [1][2][3][4] food processing, 5,6 pharmaceutical industry, [7][8][9][10] gasification and pyrolysis reactors, [11][12][13][14] and catalytic polymerization reactors. 15,16 A conical fluidized bed is a hybrid gas-solid contacting system, and therefore shares the characteristics of both fluidized and spouted beds. The naming of these types of beds in the literatures is often informed by their geometrical shape and the ratio of bed inlet diameter to particle size. 3,17 This bed provides means for the good mixing and circulation for small solid particles with a wide size distribution. Therefore, knowledge on the hydrodynamics of gas and particle flow in conical fluidized bed is essential for their design at both labscale and in industrial applications.Extensive research has been conduced on the fluidization behavior of classical powders in the 30 to 1000 lm size range 18 and, consequently, their behavior is relatively well understood. [19][20][21][22]23 studied the effect of fine particles beds with a wide size distribution on local voidage in a bench-scale conical fluidized bed. Their main conclusion is that fines form a monolayer around the relatively coarser particles and act as a lubricant, thus lowering the apparent bed viscosity. A lower apparent viscosity corresponded to smooth fluidization with fine bubbles. Geldart 19 argued that the effect observed could be explained by the reduction in mean particle diameter due to the addition of fines. Geldart's Correspondence concerning this article should be addressed to A. Bahramian at bahramian@profs.hut.ac.ir. 730AIChE Journal March 2012 Vol. 58, No. 3 measurements for Geldart A powder revealed a definite influence of size dis...

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Hydrodynamic analysis of dilute gas—solids flow in a vertical pipe

Cited by 82 publications

References 16 publications

Effect of slip boundary conditions on the simulation of microparticle velocity fields in a conical fluidized bed

Effect of slip boundary conditions on the simulation of microparticle velocity fields in a conical fluidized bed

The influence of multiple tubes on the tube-to-bed heat transfer in a fluidised bed

Fluidization of micronic particles in a conical fluidized bed: Experimental and numerical study of static bed height effect

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