利用電腦模擬探討表面具有圖案結構之薄膜的抗阻塞效應

Abstract

隨著人類對水資源品質的要求逐年提升，薄膜過濾已經成為現今業界相當常見的技術。薄膜過濾具備操作難度不高和耗費較少能源的優勢，但缺點是過程中膜上容易產生結垢，因此如何有效防止膜表面的阻塞是一大課題。在膜上設計圖案結構是一種低成本且有效的作法，不只增加過濾面積，結構本身也會影響膜表面的流場與剪應力，因而得以阻止結垢形成。本研究團隊在過往的研究中於膜上設計一種箭頭圖案結構，並以互為相反的兩道水流方向進行薄膜過濾實驗，透過比較兩者的牛血清白蛋白(BSA)之沉積分佈，確認圖案結構和流向會影響抗結垢效果。為了理解圖案結構導致抗阻塞的機制，並在後續的研究中設計抗結垢效果更佳的圖案，因此在本研究中我們以模擬的方式探討造成該現象的原因與細節。 我們首先透過COMSOL Multiphysics®模擬和分析微流道中的流場，接著以Fortran程式對粒子的落點分佈進行預測並繪製沉積分佈圖，並與實驗結果相互比較。我們由模擬發現在相反流向的條件下，在膜表面與箭頭圖案結構附近會形成兩種水流樣態與分流/匯流作用，在箭頭圖案結構頂部的剪應力也確實皆比膜底部的剪應力為高。然而在相反流向設定的模擬結果中，箭頭圖案結構頂部的剪應力之大小與分佈卻基本上相同，而膜表面的壓力與滲透流速分佈也幾乎一致，但在相反流向條件的實驗中卻能有不同的粒子沉積分佈，因此我們認為導致不同抗結垢效應的關鍵為膜表面的水流方向。我們發現傾斜通道中的支流在相反流向下對粒子移動的影響機制和效果不同，因此推測支流透過將粒子導向至膜表面不同處之上附著，進而導致不同的抗結垢效果。 在模擬中，我們從相反流向下在渠道上的粒子沉積量差異，確認箭頭圖案結構達到使水流改變方向並轉移粒子至不同處的效果，然而與我們預計不同的是，在相反流向的模擬中，粒子在箭頭圖案上之沉積位置分佈相去不遠，但相反流向條件下的實驗結果中，箭頭圖案上的粒子沉積量卻有明顯的差異。對於模擬預測與實驗結果不相符的現象，我們認為是因為我們在模擬中過度簡化粒子黏著在膜上的機制所導致，而實際上粒子能否附著在膜上尚有更多原因得以探討，因此後續對圖案結構的改良設計可以由此方面著手。

As the demand for high-quality water resources continues to rise, membrane filtration has become a widely adopted technology across various industries. This technique offers advantages such as low operational complexity and reduced energy consumption. However, membrane fouling remains a significant challenge. One cost-effective and practical strategy to mitigate fouling is to introduce patterned structures on the membrane surface. These patterns not only increase the effective filtration area but also alter the local flow field and shear stress, thereby helping to prevent foulant accumulation. In our previous work, we designed an arrow-shaped surface pattern on the membrane and conducted filtration experiments under two opposing flow directions. By comparing the deposition distributions of bovine serum albumin (BSA), we confirmed that both the pattern geometry and flow direction significantly influence anti-fouling performance. To better understand the mechanism behind this effect and to guide the future design of more effective patterns, this study investigates the phenomenon through numerical simulation. We first simulated and analyzed the flow field in a microchannel using COMSOL Multiphysics®, followed by predicting the distribution of particle deposition with a Fortran-based program to generate the figure of particle deposition, which were then compared with experimental results. The simulations revealed that, under opposite flow directions, two distinct flow characteristics and bypass/confluence behaviors developed near the arrow pattern. The shear stress on top of the arrow patterns was consistently higher than that at the bottom. However, the magnitude and distribution of shear stress at the top remained nearly identical between the two flow directions. Similarly, membrane surface pressure and permeate flux distributions showed little variation. Despite these similarities, the experimental results demonstrated clear differences in particle deposition patterns, suggesting that the key factor influencing anti-fouling behavior is the direction of surface flow. Further analysis showed that secondary flows in the inclined channels affected particle trajectories differently under the two flow directions. These flows are believed to redirect particles to distinct areas on the membrane, resulting in different anti-fouling effects. In the simulations, we confirmed that the arrow-shaped pattern was able to alter flow direction and particle transport, as reflected by differences in deposition amounts under opposite flow conditions. However, contrary to expectations, the simulated particle landing locations on the arrow patterns themselves showed minimal variation. In contrast, experimental results exhibited significant differences in particle deposition on the pattern. We attribute this discrepancy to oversimplified assumptions in the simulation regarding particle adhesion mechanisms. In reality, particle attachment may be influenced by a range of additional factors, indicating a direction for further refinement in the design of surface patterns.