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- Darelius, Anders, 1977, et al.
(författare)
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A Volume-Based Multi-Dimensional Population Balance Approach for Modelling High Shear Granulation
- 2006
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Ingår i: Chemical Engineering Science. ; 61, s. 2482-2493
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Tidskriftsartikel (refereegranskat)abstract
- A volume-based multi-dimensional population balance model based on the approach used by Verkoeijen et al. (2002) is further developed and applied to a wet granulation process of pharmaceutically relevant material, performed in a high shear mixer. The model is improved by a generalization that accounts for initial non-uniformly distributed liquid and air among the different particle size classes. Only the wet massing period of the granulation process has been modelled and it is experimentally found that the pores in the granules are fully saturated by liquid, i.e. no air is present in the granules during this period. Hence, an alternative model formulation is used as no model for the air in the granules is needed. Particle volume distribution, liquid saturation, liquid to solid ratio and porosity of the granules can all be modelled, as these properties can all be expressed as combinations of three model parameters, i.e. the volume fraction of solid material, total liquid fraction and the liquid fraction inside the granules. The model is also improved by introducing a new coalescence kernel and by increasing the number of size classes used. The simulated results are compared to measurements from a series of five designed experiments where impeller speed and water content are varied. It is found that the evolution of the volume, liquid saturation and porosity distributions could all be explained by fitting the compaction and coalescence rate constants.
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| 2. |
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| 3. |
- Darelius, Anders, 1977, et al.
(författare)
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Fluid dynamics simulation of the high shear mixing process
- 2010
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 164:2-3, s. 418-424
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Tidskriftsartikel (refereegranskat)abstract
- The Eulerian-Eulerian two-fluid approach for modelling multiphase flows is used to simulate the flow in a high shear mixer. The results are compared with experimental velocity profiles for the solids phase at the wall in the mixer obtained using a high speed camera (Darelius et al. Chem. Eng. Sci. 62 (2007) 2366).The governing equations are closed using relations from the Kinetic Theory of Granular Flow (KTGF) combined with a frictional stress model due to Johnson and Jackson and Schaeffer and inter-phase drag due to Wen and Yu. In addition, calculations are presented for a model with a constant particle phase viscosity (CPV). Free slip and partial slip boundary conditions for the solid phase velocity at the vessel wall and the impeller have been utilized.The results show that the bed height could be well predicted by the partial slip model, whereas the free slip model could not capture the experimentally found bed height satisfactorily. For the KTGF model, the swirling motion of the rotating torus that is formed by the moving powder bed was over-predicted and the tangential wall velocity was under-predicted, probably due to the fact that the frictional stress model needs to be further developed, e.g. to tackle cohesive particles in dense flow. The CPV model gave predictions in good agreement with the experiments for a solids viscosity of 0.1. Pa. s and a wall slip parameter of 0.005. m/Pa. s. However, for a very low or very high value of the particle phase viscosity and for a high value of the wall slip parameter the agreement with experiments was poor. Interestingly, values of the viscosity that are commonly employed for fluidized beds seem applicable also in the present case. © 2009 Elsevier B.V.
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| 4. |
- Darelius, Anders, 1977, et al.
(författare)
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High shear wet granulation modelling - a mechanistic approach using population balances
- 2005
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Ingår i: Powder Technology. ; 160, s. 209-218
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Tidskriftsartikel (refereegranskat)abstract
- A population balance approach based on splitting the coalescence kernel into two factors, the first describing the collision frequency of particles and the second describing the collision efficiency, is applied to modelling wet granulation in a high shear mixer. Four different expressions for the collision frequency are compared and discussed. The kernels are the size independent kernel, the shear kernel proposed by Smoluchowski [1] and the two kernels proposed by Hounslow [2], i.e. the EKE kernel and the less used kernel based on equipartition of fluctuating translational momentum (ETM kernel). Microcrystalline cellulose (mcc) is granulated under different process conditions and it is found that the ETM kernel best describes the granulation at higher impeller speeds, whereas the EKE kernel gives better agreement at lower impeller speeds. The collision efficiency is assumed to be a function of the liquid saturation. By using this assumption, it was possible to detect similar trends for the remaining part of the collision efficiency regardless of process conditions.
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| 5. |
- Darelius, Anders, 1977, et al.
(författare)
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LDA measurements of near wall powder velocities in a high shear mixer
- 2007
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 62:21, s. 5770-5776
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a new method has been developed to measure particle velocity distributions in the near wall region of a high shear mixer by using Laser Doppler Anemometry (LDA). The velocities along the side of the granulator have been measured at different impeller speeds and it has been found that it is possible to obtain tangential and axial velocity data in the dense powder flow up to 4 mm in depth. Moreover, it has been found that the tangential velocity component increases slightly with distance from the wall in the near wall region, indicating a partial slip boundary condition for the solid phase at the vessel wall. It is also shown that the tangential velocity decreases with increased vertical distance to the impeller. The velocity fluctuations, represented by root mean square (rms) velocities, also decrease with increased vertical distance to the impeller and the tangential and axial rms components are found to be of the same order of magnitude.
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| 6. |
- Karlsson, Stina, 1975, et al.
(författare)
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CFD modelling of the Wurster bed coater.
- 2009
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 55:10, s. 2578-2590
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Tidskriftsartikel (refereegranskat)abstract
- In the Wurster bed coater, the wetting, drying, and circulation of particles are combined to produce a high quality coating. The drying and wetting conditions in a laboratory scale Wurster bed coater are modeled and compared with experimental data. A model combining multiphase fluid dynamics with heat and mass transfer is developed to model the particle and gas motion and the transport of thermal energy and moisture. A wetting region is defined, where a specified moisture content is set in the particle phase, above the jet inlet, to describe the injection ofcoating liquid. The simulation shows the characteristic circulation of particles in the equipment, as well as the behavior of the moisture in the system and agrees well with measurements. The simulation indicates how different process conditions influence the drying regions. The results show that most ofthe drying, under typical operating conditions, takes place in the Wurster tube. © 2009 American Institute of Chemical Engineers.
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| 7. |
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| 8. |
- Nguyen, Duy, 1986, et al.
(författare)
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Mechanistic time scales in adhesive mixing investigated by dry particle sizing
- 2015
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Ingår i: European Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0928-0987 .- 1879-0720. ; 69, s. 19-25
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Tidskriftsartikel (refereegranskat)abstract
- This study exploits the mechanisms governing blending of adhesive mixtures, i.e. random mixing, deagglomeration and adhesion, and their relative importance to achieve mixing homogeneity. To this end, blending of micronized particles (fines) with carrier particles was carried out using a high shear mixer. Dry particle sizing using laser diffraction coupled with a strong powder dispersion unit was employed to measure the fines content in samples collected during mixing, and hence to assess blend homogeneity. The method was also employed to evaluate the relative strength of the agglomerates present in the fines. Particle sizing using a non-destructive imaging technique was used to monitor changes in particle size during blending. It could be shown that the de-agglomeration of the fine-particle agglomerates is the slowest mechanism and hence the rate-limiting step as regards achieving a homogeneous adhesive mixture. Consequently, a longer mixing time is needed for blending of larger agglomerates. Being fast, simple and reproducible, the laser diffraction technique was shown to be an efficient method for measurement of fine particle content and homogeneity of a mixture, while the non-destructive image analysis was able to give relevant information on the rate of de-agglomeration of the fine-particle agglomerates as well as on the size of the resulting carrier-fine particle assemblies.
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| 9. |
- Niklasson Björn, Ingela, 1960, et al.
(författare)
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Empirical to mechanistic modelling in high shear granulation
- 2005
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Ingår i: Chemical Engineering Science. ; 60, s. 3795-3803
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Tidskriftsartikel (refereegranskat)abstract
- This paper gives an overview of the different models available for granulation in high shear mixers with a focus on applicability in the pharmaceutical industry. Three examples of applications are given. The examples indicate the potential of mechanistically based models for scale-up and the importance of understanding the dynamics of the granulation process. The first two examples show how the impeller torque can be modelled and predicted in the dry and wet mixing phases of the high shear granulation process, using a solid mechanics and a hierarchical multivariate model, respectively. In the third application the particle size distribution is modelled using population balances and it is shown how different operating conditions can be included in the coalescence kernel to describe the granule growth.
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| 10. |
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| 11. |
- Niklasson Björn, Ingela, 1960
(författare)
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Intermediate heat exchange in binary distillation
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AbstractThe overall reason for investigating intermediate heat exchange in diabatic distillation is to enable a reduction in external energy demand.This thesis applies computer simulations and experimental measurements to evaluate and analyse the use of intermediate heat exchange in binary distillation. The use of intermediate heat exchange has been studied in a stand-alone distillation unit as a method to improve the energetic performance of distillation. Considerable external energy savings can theoretically be achieved by using different intermediate heat exchange arrangements.The way the intermediate heat exchange is performed in terms of a combination of positions for side stream withdrawal and side stream return has a clear impact on the column performance.In a real column with constant number of trays and constant separation an optimisation of the intermediate heat exchange will generate increased efficiencies locally together with improved separation. Some parts will run closer to reversibility than other parts. A new type of experimental equipment has been constructed to enable pilot plant scale diabatic distillation experiments in both the rectifying section as well as in the stripping section.
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