Hydrodynamic approach to dissolution rate
Hydrodynamic approach to dissolution rate
复制标题
溶解速率的流体动力学方法
作者：
H. Grijseels;D. Crommelin;C. J. Blaey
在药学文献中，固体在液体中的溶解通常用停滞层模型来描述。然而，这个模型并不反映所涉及的流体动力学的实际情况。这篇综述分析了溶解可能发生的不同流体动力学情况，似乎在强迫对流下，在层流和湍流中，规则的非崩解表面的溶解可以用数学描述。这同样适用于平行于垂直溶解表面的层流自然对流中的溶解。所有这些情况都可以使用溶解速率（R）的通用表达式来处理，该通用表达式包含五个基本参数，即溶解度（Cs）、扩散系数（D）、运动粘度（v）、流速（u）和作为溶解表面的形状和尺寸的函数的几何因子（A），因此
$$R = KC_S D^eta { ext{ }}v^gamma { ext{ }}u^F A$$
指数B、γ和ε、比例因子K和几何因子A（定义为A = f（B，l，r，d））取决于溶剂运动的每种特定情况下的流体动力学条件。这些值中的大多数是从理论上推导出来的，并得到了实验的证实。与此相反，它似乎是不可能的，目前描述的溶解过程中自然对流条件下，如果流动是不平行的溶解surface.In结论是显而易见的，分析溶解过程中，使用流体动力学理论，提供了一个更好的洞察力的过程本身和影响它的因素，定性和定量。只有这样才能正确解释实际溶出速率数据。
AbstractIn the pharmaceutical literature the dissolution of solids in liquids is usually described using the stagnant layer model. This model, however, does not reflect the actual situation with respect to the hydrodynamics involved. This review analyses the different hydrodynamic situations in which dissolution may take place.It appears that dissolution of regular, non-disintegrating surfaces under forced convection, in laminar as well as in turbulent flow, can be described mathematically. The same holds true for dissolution in a laminar natural convection flow parallel to a vertical dissolving surface. All these situations can be treated using a general expression for the dissolution rate (R) containing five basic parameters,i.e. solubility (Cs), diffusion coefficient (D), kinematic viscosity (v), flow velocity (u) and a geometric factor (A) which is a function of the shape and dimensions of the dissolving surface, thus
$$R = KC_S D^eta { ext{ }}v^gamma { ext{ }}u^F A$$
The exponentsΒ,γ andε, the proportionality factor K and the geometric factor A, which is defined as A = f (b, l, r, d), depend on the hydrodynamic conditions in each particular case of solvent motion. Most of these values were derived theoretically and confirmed experimentally. In contrast to this it appears to be impossible at present to describe the dissolution process under natural convection conditions if the flow is not parallel to the dissolving surface.In conclusion it is evident that analysing dissolution processes, using hydrodynamic theories, provides a better insight in the process itself and the factors influencing it both qualitatively and quantitatively. Only this will permit correct interpretation of actual dissolution rate data.