Stabilising effect of topography on thin film flows for coating applications

在倾斜的固体衬底上流动的液体薄膜具有形成以一致形状和特征速度传播的振幅较大的自由表面波的倾向-这是一种常见的和众所周知的不稳定性。毫不奇怪，在流体层表面出现这种波浪图案是许多技术应用中不希望出现的特征，这些技术应用涉及与印刷制造过程相关的涂层操作；例如太阳能电池的制造或纸张的生产。现有的实验数据表明，膜流与包含重复地形特征的基底的相互作用能够延迟不稳定的开始，从而导致更高的地形依赖于不稳定开始的临界条件。然而，虽然文献中有关于周期性地形流动的理论模型，但到目前为止，还没有证据表明其中任何一个模型能够预测和捕获实验观察到的稳定效应。因此，该项目的目的是开发能够在尽可能广泛的控制参数范围内预测导致自由表面不稳定开始的条件的理论模型。通过开发这样的模型，了解所涉及的参数的相互作用，并确定无缺陷涂层的安全操作窗口，有可能完全消除或最小化它们在工业环境中的有害影响，使制造商能够预测和利用操作窗口和条件，保证生产测量稳定的膜。为此目的，该项目将涉及与学术界和工业界代表的合作。

Thin liquid films flowing over an inclined solid substrate have the propensity to form large-amplitude free-surface waves propagating with a coherent shape and characteristic speed - a commonly observed and well-known instability. Not surprisingly, the appearance of such wave patterns, on the surface of a fluid layer, is an unwanted feature in many technological applications involving coating operations connected to print manufacturing processes; for example the manufacture of solar cells or paper production.Existing experimental data shows that the interaction of the film flow with substrate that contains repeating topographic features is able to delay the on-set of instability resulting in a higher topography-dependent critical condition for the onset of instability. However, while there are theoretical models for flow over periodic topography available in the literature, until now no evidence has appeared showing that any of them are able to predict and capture the experimentally observed stabilisation effects. The purpose of the project is therefore to develop theoretical models capable of predicting the conditions leading to the onset of free-surface instability for as wide a range as possible of the governing parameters of interest. By developing such models, to understand the interaction of the parameters involved and to identify safe operating windows for defect free coating, there is the potential to either eliminate completely or to minimise their detrimental effects in an industrial context, by enabling manufactures to predict and utilise operating windows and conditions that guarantee the production of a metered steady film. To this end, the project will involve collaboration with representatives from both academia and industry.