Kakhi Maziar
Food and Drug Administration, Division of Pharmaceutical Analysis, Silver Spring, MD 20993, USA.
Int J Pharm. 2009 Jul 6;376(1-2):22-40. doi: 10.1016/j.ijpharm.2009.04.012. Epub 2009 Apr 16.
The fluid dynamics in the flow-through cell (USP apparatus 4) has been predicted using the mathematical modeling approach of computational fluid dynamics (CFD). The degree to which flow structures in this apparatus can be qualified as 'ideal' both spatially and temporally has been assessed. The simulations predict the development of the velocity field in this apparatus for configurations with and without beads during the discharge stroke of the pump. When the cell is operated only with the red ruby bead ('open column' mode), highly non-uniform flow is predicted just downstream of the bead in the latter stages of the pump's pulse. In contrast, a strong degree of profile uniformity and symmetry is predicted throughout the entire pulse in the region of the tablet holder for both standard configurations involving beads. However, noticeable differences in the tablet shear stress distribution are predicted at times when the same instantaneous inlet flow rates are being pumped through the apparatus. This effect is caused by flow separation in the velocity boundary layer formed around the tablet under the influence of an adverse pressure gradient, an effect not predicted with constant (non-pulsating) flow. While the degree of tablet erosion correlates with the average flow rate, during a particular pulse both the free-stream velocity and the boundary layer thickness are also influential.
已使用计算流体动力学（CFD）的数学建模方法预测了流通池（USP装置4）中的流体动力学。评估了该装置中流动结构在空间和时间上可被视为“理想”的程度。模拟预测了在泵的排出冲程期间，该装置中有无珠子情况下的速度场发展情况。当流通池仅使用红色红宝石珠运行（“开放柱”模式）时，预测在泵脉冲后期珠子下游会出现高度不均匀的流动。相比之下，对于两种涉及珠子的标准配置，预测在整个脉冲期间片剂保持器区域内的轮廓均匀性和对称性都很高。然而，当以相同的瞬时入口流速泵送流体通过该装置时，预测片剂剪切应力分布会有明显差异。这种效应是由在不利压力梯度影响下片剂周围形成的速度边界层中的流动分离引起的，这种效应在恒定（非脉动）流动中无法预测。虽然片剂侵蚀程度与平均流速相关，但在特定脉冲期间，自由流速度和边界层厚度也有影响。
