| 1. |
- Abrahamsson, Per, 1985, et al.
(author)
-
CONTINUUM MODELING OF PARTICLE FLOWS IN HIGH SHEAR GRANULATION
- 2013
-
In: 6th International Granulation Workshop.
-
Conference paper (peer-reviewed)abstract
- High shear granulation (HSG) is a common process in the pharmaceutical industry. A better understanding of the flow conditions of powders and granulates in large-scale HSG equipment is crucial for constructing predictive models. The staggering amount of particles in the process makes the use of continuum flow models highly attractive. This article discusses the possibilities and problems in using continuum modelling in HSG systems and evaluates some of the available modelling approaches. We examine several dense granular flow models studying both the underlying theory and how they perform in practice. The studied models are the frictional model by Shaeffer [1], modifications to the transport coefficients that describe the solid phase stresses similar to those used in Khain and Meerson [2], and the framework developed by Jop et.al. [3] using a depth-averaged flow model for constant solid volume fraction flows.The model by Shaeffer has previously been used with the conclusion that the solid phase stresses are underestimated [4]. We show theoretically and in practice that this approach is not appropriate due to the strong resolution dependence of the model. The approach taken by Khain and Meerson, among others, to try to modify expressions from rapid granular flow to also be valid in the dense region is attractive from a theoretical point of view. Making use of the rigorous framework of kinetic theory, the applicability of a number of such models to HSG has been evaluated. The modelling framework developed by Jop et.al was used in disc impeller HSG equipment. The results show that the model can well predict the behaviour of the solid-phase viscosity of the dense granular flow. The model is nevertheless restricted to constant volume fraction flows and needs to be expanded to include a varying volume fraction. We conclude in this paper that continuum modelling of HSG has a promising outlook but there is a need to develop better models for the dense regions of the flow. We also give and evaluate some of the options available for treating these regions.
|
|
| 2. |
|
|
| 3. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
A regime map for the normal surface impact of wet and dry agglomerates
- 2018
-
In: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 64:6, s. 1975-1985
-
Journal article (peer-reviewed)abstract
- The normal surface impacts of wet and dry agglomerates are simulated in a DEM framework. While the impact behavior of dry agglomerates has been addressed previously, similar studies on wet agglomerate impact are missing. We show that by adding a small amount of liquid the impact behavior changes significantly. The impact behavior of the agglomerates at different moisture contents and impact energies are analyzed through post-impact parameters and coupled to their microscopic and macroscopic properties. While increasing the impact energy breaks more inter-particle bonds and intensifies damage and fragmentation, increasing the moisture content is found to provide the agglomerates with higher deformability and resistance against breakage. It is shown that the interplay of the two latter parameters together with the agglomerate structural strength creates various impact scenarios, which are classified into different regimes and addressed with a regime map.
|
|
| 4. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
Characterization of force networks in a dense high-shear system
- 2018
-
In: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 38, s. 215-221
-
Journal article (peer-reviewed)abstract
- We detect the strong force networks in a dense high shear system and we study their structure and stability in response to the variation of the shearing rate. The presence of strong force networks, which are usually of heterogeneous structure, restricts particle movements and can impose non-local mechanisms of momentum transfer. We identify such networks in a dense high shear system through the algorithm of community detection. Moreover, we explain the association between the mechanisms of momentum transfer and the structure, population, strength and stability of the force networks by tracking the spatial and temporal evolution of the detected networks. In addition, we show that the assumption of a monodispersed assembly of particles leads to an unrealistic enlargement of the force networks, underestimating both the rate of energy dissipation and the rate of mixing.
|
|
| 5. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
Continuum modeling of multi-regime particle flows in high-shear mixing
- 2015
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 280, s. 67-71
-
Journal article (peer-reviewed)abstract
- This article compares and evaluates different approaches for continuum modeling in high shear mixers coveringthe full range of the solid volume fraction. High shear mixing is considered as the first stage in industrial highshear granulation processes. The study is focused on and compared with experimental data for a MiPro mixer.Different granular flow regimes are located in different regions of the system and suitable models are appliedfor each region. Accordingly, the dilute regions are modeled with the standard kinetic theory of granular flow(KTGF) model. The dense regions are modeled using a framework developed by Jop et al. [1] which treatsdense flows with pseudo-plastic rheology. The transitional region from dilute to dense is either modeled withKTGF or by using modifications to the transport coefficients that describe the solid phase stresses as proposedby Bocquet et al. [2] (the viscosity divergence model). The results using the latter model show significant improvementcompared to similar studies in the past. A very good agreement between simulation and experimentsis achieved. It should be noted that the proposed modeling frameworks are formulated for the full range ofvolume fractions and can be applied to various particulate flows. To sum up, this research provides a betterdescription of multi-regime granular flows, particularly the transitional behavior in the intermediate range ofvolume fractions
|
|
| 6. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
Modeling dilute and dense granular flows in a high shear granulator
- 2014
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 263, s. 45-49
-
Journal article (peer-reviewed)abstract
- This study models a high shear granulation system, including both dense and dilute regions. The dense region is modeled using an approach in which the system is treated as a visco-plastic fluid and the rheology of such a fluid is evaluated. The dilute regions are modeled by the standard Kinetic Theory of Granular Flow (KTGF). The switching between the models is accounted for by using the dimensionless inertial number, defined as the ratio shear forces/pressure forces. The results compare favorably with experimental data for a disk impeller high shear granulator. Granular temperatures and volume fractions, in particular, are well captured by the aforementioned model. The velocity profiles show better agreement with experimental data as compared to previous studies. (C) 2014 Elsevier B.V. All rights reserved.
|
|
| 7. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
Multiscale rheophysics of nearly jammed granular flows in a high shear system
- 2017
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 315, s. 356-366
-
Journal article (peer-reviewed)abstract
- We investigate non-local features of granular flows in nearly jammed configurations. We identify the presence of contact networks and crystallization as the reasons for such a behavior and perform Discrete Element Simulations on a high shear disk impeller granulator. The association of particle properties (e.g. the coefficients of restitution and friction) with the observed flow structures is studied using multivariate data analysis and multilinear optimization. The effect of polydispersity on the structure of the contact networks is studied. A singularity in the momentum flux is observed when approaching a monosized particle assembly, implying the onset of crystallization. Macroscopic quantities, such as the velocity profiles and momentum flux, are linked to microscopic data from DEM simulations through several statistical methods: the spectral analysis (giving dominant frequencies of the flow), coordination numbers that map the local flow regimes and the pair correlation function that is weakly associated with the variations of the flow structure. (C) 2017 Elsevier B.V. All rights reserved.
|
|
| 8. |
- Khalilitehrani, Mohammad, 1984
(author)
-
Rheological modeling of particle flows in high shear granulation
- 2014
-
Licentiate thesis (other academic/artistic)abstract
- High shear granulation is an important process in a wide variety of applications, more specifically in pharmaceutical industries as a basic step in the tableting process. The process includes two major steps: dry high shear granulation and wet high shear granulation. It aims at producing granules with a specific size and material composition. The quality of the process is determined by the flow regime. Therefore, a better understanding of the flow regime is required. Computational simulation of such systems is traditionally performed by tracking each particle and resolving its binary collision and interaction with other particles. This approach is not feasible for industrial granulators with billions of particles. The aim of this study is to evaluate the possibility of applying various continuum modeling options in studying dense or multi-regime granular flows. Kinetic Theory of Granular Flow formulates the dilute parts of the system, whereas there is no strong agreement on any approach to modeling dense granular flows. In this study, a recent model proposed by Jop et al. is applied as an alternative to the model by Schaeffer, traditionally used for such flow regimes.The results show that the present model is not only simple, but also clearly predictive. Besides, considering the simplicity of the model compared to its alternatives (KTGF or DEM), adding more details to develop the model can be performed with fewer obstacles. In order to validate the model proposed in this study, model results are compared with experiments performed in a disc impeller granulator. The experimental results were analyzed using advanced techniques including a high speed camera and Particle Image Velocimetry (PIV). Keywords: high shear granulation, continuum modeling, rheology, disc impeller
|
|
| 9. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
The morphology of the deposited particles after a wet agglomerate normal surface impact
- 2019
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 345, s. 796-803
-
Journal article (peer-reviewed)abstract
- Through discrete element modeling, we investigate the breakage, deposition and attachment of wet dust agglomerates during normal surface impacts. The morphology and structure of the deposited dirt layer is studied through statistical analysis of the height profiles. It is found that the deposited layer is influenced by both the structural properties of the primary agglomerates and the impact conditions. The roughness of the deposited dirt layer shows a positive correlation to impact velocity and a negative correlation to the agglomerate moisture content. Within the pendular liquid regime the structural strength of the agglomerates shows a strong correlation to the moisture content while at higher moisture content the correlation becomes weaker. It is also observed that for a given impact velocity agglomerates of various sizes show similar deposition patterns. To unify the results for different agglomerate sizes, a dimensionless surface density is introduced.
|
|
| 10. |
- Khalilitehrani, Mohammad, 1984, et al.
(author)
-
The rheology of dense granular flows in a disc impeller high shear granulator
- 2013
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 249, s. 309-315
-
Journal article (peer-reviewed)abstract
- The aim of the present study is to evaluate the new approach to dense particulate systems proposed by Jop et al. [1],in the dense regions of a High Shear Granulator (HSG). Wet granulation in high shear mixers is a common processin pharmaceutical technologies and a good understanding of the local mixing and flow patterns is a pre-requisitefor this step. In the aforementioned model a dense granularflow is characterized as a visco-plasticfluid. Thereforethe local rheology of the system can be predicted assuming averaged and virtual properties and a constant solidvolume fraction.A simple disc impeller granulator with glass spheres was chosen for this study. The dynamics of the system havebeen studied using several techniques including PIV analyses, CFD simulation and image processing. The flowbehaviour has been characterized for various impeller speeds and particle loads. Several cases have been analyzedfrom different aspects both in experiments and through equivalent simulations to evaluate the validity of themodel in these particular applications.Results look promising in spite of the simplicity of the model. The model was found to give a good generaldescription of the flow field and bed shape. On the other hand the model is insufficient in some aspects; mostlyrelated to the regions with low volume fraction. The next step would be to combine the model with conventionalmodels on rapid granular flow such as Kinetic Theory of Granular Flows (KTGF).
|
|
