P. Martin-Salvador, R. H. Verschueren, T. De Beer, A. Kumar
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Therefore, such coating processes are challenging to optimize, given the complex phenomena involved in fluidization, plasma species reactions, and surface reactions. In this study, we use the CFD-DEM approach as implemented in the CFDEM®coupling package to model the process. The functionalization rate is modeled as mass transfer from the surrounding gas onto the particles, using a plasma coating zone where this transfer may happen. Mass transfer is switched off outside this zone. The DEM contact parameters and drag force are calibrated to our cellulose beads model powder using experimental tests composed by the FT4 rheometer and spouting tests. We show that while the chemistry can make or break the process, the equipment design and process conditions have a non-negligible effect on the coating metrics and thus must be considered. 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引用次数: 0
摘要
用于药用粉末颗粒表面功能化的冷等离子涂层技术是一种很有前途的方法,可引入新的特性,如控制释放层、改善粉末流动特性、稳定涂层以及将活性成分结合到表面。这通常是在流化床反应器中实现的,其中包含化学前体和等离子余辉的射流通过喷嘴引入,同时从底板注入额外的流化气体。然而,该工艺需要在等离子体活性区内适当混合颗粒和前驱体,以确保所有颗粒的涂层均匀一致。因此,考虑到流化、等离子体物种反应和表面反应所涉及的复杂现象,此类涂层工艺的优化具有挑战性。在本研究中,我们使用 CFDEM®coupling 软件包中的 CFD-DEM 方法来模拟该过程。功能化速率被模拟为从周围气体到颗粒的质量转移,并使用等离子涂层区来实现这种转移。在该区域外,质量转移被关闭。我们使用 FT4 流变仪和喷射试验对 DEM 接触参数和阻力进行了校准。我们的研究表明,虽然化学成分可以决定工艺的成败,但设备设计和工艺条件对涂层指标也有不可忽视的影响,因此必须加以考虑。流化流量不足以产生良好混合的情况下,涂层质量的变化系数较高,因此必须避免。此外,我们还提出了一种外推程序,以提供更长涂层时间下的结果,这表明,即使对超过一分钟的过程进行模拟的计算效率不高,也可以预测涂层性能。
CFD-DEM model of a cold plasma assisted fluidized bed powder coating process
Cold plasma coating technology for surface functionalization of pharmaceutical powder particles is a promising approach to introduce new characteristics such as controlled release layers, improved powder flow properties, stability coatings, and binding of active components to the surface. This is typically achieved in a fluidized bed reactor, where a jet containing the chemical precursor and the plasma afterglow is introduced through a nozzle while extra fluidization gas is injected from the bottom plate. However, the process requires proper mixing of the particles and precursor inside the plasma active zone to ensure a homogeneous coating of all particles. Therefore, such coating processes are challenging to optimize, given the complex phenomena involved in fluidization, plasma species reactions, and surface reactions. In this study, we use the CFD-DEM approach as implemented in the CFDEM®coupling package to model the process. The functionalization rate is modeled as mass transfer from the surrounding gas onto the particles, using a plasma coating zone where this transfer may happen. Mass transfer is switched off outside this zone. The DEM contact parameters and drag force are calibrated to our cellulose beads model powder using experimental tests composed by the FT4 rheometer and spouting tests. We show that while the chemistry can make or break the process, the equipment design and process conditions have a non-negligible effect on the coating metrics and thus must be considered. Cases where the fluidization flow is not high enough to produce good mixing have a high coefficient of variation of the coating mass, and therefore, they must be avoided. In addition, we also proposed an extrapolation procedure to provide results at longer coating times, showing that it is possible to predict coating performance even when simulations of the process for more than a minute are not computationally efficient.