| 1. |
- Li, Liang, 1987, et al.
(author)
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Effect of drag models on residence time distributions of particles in a wurster fluidized bed: A DEM-CFD study
- 2016
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In: KONA Powder and Particle Journal. - : Hosokawa Powder Technology Foundation. - 0288-4534 .- 2187-5537. ; 2016:33, s. 264-277
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Journal article (peer-reviewed)abstract
- Fluidized bed coating has been used to coat pellets or tablets with functional substances for a number of purposes. In this coating process, particle wetting, drying and film formation are coupled to particle motion. It is therefore of interest to study particle motion in such fluidized beds and to use the results to develop a model for predicting the quality of the final product. In this paper, we present results from DEM-CFD simulations, i.e. discrete element method and computational fluid dynamics simulations of particle motion in a laboratory-scale Wurster fluidized bed that was also employed in positron emission particle tracking (PEPT) experiments. As the drag force is the dominant interaction between the gas flow and the particle motion in this type of fluidized bed, the effect of drag models on the particle motion is investigated. More specifically, the particle velocity and residence time distributions of particles in different regions calculated from five different drag models are presented. It is found that the Gidaspow and Tang drag models predict both particle cycle and residence times well. The HKL and Beetstra drag models somewhat overestimate the particle velocity in the Wurster tube and therefore predict a reduced number of recirculations and a significantly shorter cycle time.
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| 2. |
- Li, Liang, 1987, et al.
(author)
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Residence time distributions of different size particles in the spray zone of a Wurster fluid bed studied using DEM-CFD
- 2015
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In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 280, s. 124-134
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Journal article (peer-reviewed)abstract
- Particle cycle and residence time distributions in different regions, particularly in the spray zone, play an important role in fluid bed coating. In this study, a DEM-CFD (discrete element method, computational fluid dynamics) model is employed to determine particle cycle and residence time distributions in a laboratory-scale Wurster fluid bed coater. The calculations show good agreement with data obtained using the positron emission particle tracking (PEPT) technique. The DEM-CFD simulations of different size particles show that large particles spend a longer time in the spray zone and in the Wurster tube than small particles. In addition, large particles are found on average to move closer to the spray nozzle than small particles, which implies that the large particles could shield small particles from the spray droplets. Both of these effects suggest that large particles receive a greater amount of coating solution per unit area per cycle than small particles. However, the simulations in combination with the PEPT experiments show that this is partly compensated for by a longer cycle time for large particles. Large particles thus receive more coating per unit area per pass through the spray zone, but also travel through the spray zone less frequently than small particles.
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