Mixing and Segregation Characteristics of Binary Granular Material in Tapered Fluidized Bed: A CFD Study

Sutar, Harekrushna; Das, Chandan

doi:10.4236/eng.2012.44029

Cited by 5 publications

(3 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A particular case is when there is very localized influx of fluid, leading to a spatial heterogeneity of the phenomenon, this situation is generally termed localized fluidization in the literature. Such a configuration appears in tapered fluidized bed reactors found in many industrial process (drying, coating crystallization, mixing, etc) [7,8], spouted beds, or in some natural geological formations [9]. Eventually, fluidized zones induced by underground pipe leakage are also a major concern as ground surface may collapse due to the leak, causing important accidents [10].…”

Section: Introductionmentioning

confidence: 99%

Localized fluidization in granular materials: Theoretical and numerical study

et al. 2016

View full text Add to dashboard Cite

We present analytical and numerical results on localized fluidization within a granular layer subjected to a local injection of fluid. As the injection rate increases the three different regimes previously reported in the literature are recovered: homogeneous expansion of the bed, fluidized cavity in which fluidization starts developing above the injection area, and finally the chimney of fluidized grains when the fluidization zone reaches the free surface. The analytical approach is at the continuum scale, based on Darcy's law and Therzaghi's effective stress principle. It provides a good description of the phenomenon as long as the porosity of the granular assembly remains relatively homogeneous, i.e., for small injection rates. The numerical approach is at the particle scale based on the coupled discrete element method and a pore-scale finite volume method. It tackles the more heterogeneous situations which occur at larger injection rates. The results from both methods are in qualitative agreement with data published independently. A more quantitative agreement is achieved by the numerical model. A direct link is evidenced between the occurrence of the different regimes of fluidization and the injection aperture. While narrow apertures let the three different regimes be distinguished clearly, larger apertures tend to produce a single homogeneous fluidization regime. In the former case, it is found that the transition between the cavity regime and the chimney regime for an increasing injection rate coincides with a peak in the evolution of inlet pressure. Finally, the occurrence of the different regimes is defined in terms of the normalized flux and aperture.

show abstract

Section: Introductionmentioning

confidence: 99%

Localized fluidization in granular materials: Theoretical and numerical study

et al. 2016

View full text Add to dashboard Cite

show abstract

“…This states that the solute rejected upon solidification is either back-diffused in the solid or advected into under-cooled liquid. The two transport terms on the right-hand side of the interfacial species balance contain the interfacial area concentration shown in Table 4 Equation (T-4-2) and so-called diffusion lengths expressions for which are provided in Table 4 ( Rowe et al, 1972;Agarwal, 1988). It has been shown elsewhere that the present back-diffusion model gives accurate predictions of solid micro-segregation and the final eutectic fraction.…”

Section: Model Description 31 Two-phase Modelmentioning

confidence: 93%

“…The number of grains per unit area n is needed in the expression for interfacial area concentration and the grain radius is needed in the calculation of interfacial drag, (Agarwal, 1988) and spices diffusion length, (Rowe et al, 1972) see Equations (T-4-4a), (T-4-4a) and (T-4-5b), respectively. Although, a variable grain density was found to have a relatively small effect on the predicted macro-segregation (Reddy & Beckermann, 1997) but in this study, the grain density is taken to be uniform for each control element and is equal to values as determined from the present experiments.…”

Section: Model Description 31 Two-phase Modelmentioning

confidence: 99%

Convection Streams and Macrosegregation Couple Phenomena for Dendritic Solidification Defects in Casting Processes

El-Bealy¹

2013

JMSR

View full text Add to dashboard Cite

An investigation has been performed to study the effects of convection streams and the movement of dendritic solid on the macrosegregation in equiaxed structure of aluminium cast ingots. The investigation combined laboratory work, metallographic examination and mathematical modelling. The laboratory work involved different superheats for Al-10%Si alloy cast ingots. The measurements of grain size of equiaxed crystals and macro-segregation distributions have been conducted to verify the solidification model by using the metallographic study combined macro/micro-structural evolution of cast ingot samples. Two-dimensional mathematical model of fluid flow and heat transfer has been developed to characterise the natural convection streams, thermal fields and macro-segregation distributions taken into account the effect of dendritic solid movements. The model predictions were compared to measurements of cooling curves and macro-segregation distributions where the reasonable agreements were found. The formation of macro-segregation phenomenon has been studied and discussed based on convection streams, the movements of dendritic solid and mushy permeability. Also, some typical cases in conventional casting processes related to increase the occurrence of dendritic solidification defects have been discussed.

show abstract