On the bridging mechanism in vibration controlled dispensing of pharmaceutical powders from a micro hopper
On the bridging mechanism in vibration controlled dispensing of pharmaceutical powders from a micro hopper
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DOI：
10.1016/j.powtec.2013.07.027
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发表时间：
2013-11
影响因子：
5.2
通讯作者：
G. Jasion;J. Shrimpton;Z. Li;Shoufeng Yang
中科院分区：
文献类型：
--
作者：
G. Jasion;J. Shrimpton;Z. Li;Shoufeng Yang
在数百微米的尺度上以小剂量精确批量分配药物粉末是一项具有挑战性的任务。Yang等人开发了一种新的点胶技术，利用高频振动控制粉末从狭窄料斗中流出。该方法消除了对机械阀的需要，因为粉末非常快速地形成横跨被动出口的桥状结构，防止流出。已经发现，振动的激活使桥接结构不稳定，使得粉末能够流动，当振动停止时，桥接结构快速重建并且分配停止。在这项工作中，离散元法（DEM）被用来模拟这种新的点胶控制方法，以确定内部机制，使流量得到精确控制。模拟锥形漏斗充满颗粒，然后在高频（~10 kHz）下垂直振荡，振幅和频率从实验系统缩放。模拟了两种孔板尺寸、各种离散元参数和两种振动模式。DEM参数的参数研究是基于周围的情况下，提供的实验流速的2倍内的流速。发现振动后的分配与实验中一样非常快地停止。在填充、振动和振动后立即观察内部结构，发现喷嘴出口上方漂浮着一团缓慢移动的颗粒。当振动停止时，颗粒的中心质量与壁接触并迅速堵塞流动。
Accurate batch dispensing of pharmaceutical powders, on the scale of hundreds of microns, in small doses is a challenging task. A novel dispensing technique has been developed by Yang et al. using high-frequency vibration to control powder flow out of a narrow hopper. This method removes the need for mechanical valves because the powder, very quickly, forms a bridge-like structure across the passive outlet preventing outflow. Activation of the vibration has been found to destabilise the bridging structure enabling the powder to flow, when vibration stops the bridge structure quickly rebuilds and dispensing stops. In this work the Discrete Element Method (DEM) was used to simulate this novel dispensing control method in order to identify the internal mechanism that allows the flow to be controlled so precisely. A simulated conical hopper was filled with particles then oscillated vertically at high frequency (≈ 10 kHz), amplitude and frequency were scaled from the experimental system. Two orifice sizes, a variety of DEM parameters and two vibration modes were simulated. The parametric study of DEM parameters was based around a case that provided flow rates within a factor of 2 of the experimental flow rates. Dispensing after vibration was found to stop very quickly as in experiments. Visualisation of internal structures during fill, vibration and immediately after vibration revealed a central mass of slow moving particles floating above the nozzle outlet. When the vibration stops the central mass of particles drops into contact with the walls and quickly plugs the flow.