科研之友
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摘要
A simple model of viscoplastic thin film formation flow, which is designed to describe a prototype downstream slot-coating problem, is proposed. Initially, a coating material, typically a dense suspension, is completely yielded due to an imposed shear stress caused by the stationary coating die lip and the moving substrate. After the die, the material experiences a sudden absence of shear stress at the gas/liquid interface on the top, while the bottom maintains a still shear-dominant flow. The asymptotic analysis of this film formation flow reveals that the zeroth order terms alone cannot properly explain stress evolution, hence predicting the shape and location of the yield plane inside this flow. When higher-order terms are included, an augmented pressure jump across the interface is observed in the normal stress balance due to yield stress. The results are compared with solutions of two-dimensional mass and momentum balance equations with the same constitutive equation using the finite volume method. Implications for desirable operating conditions for slot coating are discussed.
- 出版日期2016-3
