Islanabilirlik Gradyan Yüzeylerinde Kendi Kendini Yürüten ve Birleştiren Damlacıklar: Bir Lattice Boltzmann Çalışması

Abstract

Damlacıkların kendi kendine taşınması ve kontrolü, mikroakışkan cihazların geliştirilmesinde, kendi kendini temizlemede, su toplamada ve ısı transferini geliştirmede önemli bir rol oynar. Yüzeylerde bir ıslatma gradyanı yapılandırılmışsa, harici bir kuvvet olmadan damlacık manipülasyonu elde edilebilir. Temas açısı histerezisi, daha çok ıslanan tarafa doğru bir itici güç oluşturur. Bu kuvvet, hareketli temas hatlarının yakınındaki viskoz gerilimlerle dengelenirse, bu tür yüzeyler üzerindeki damlacıklar, bu denge tarafından belirlenen sabit öteleme hızına ulaşabilir. Bu çalışmada D2Q9 lattice Boltzmann yöntemi, ıslanabilirlik gradyan yüzeylerinde kendiliğinden hareket eden damlacıkların simülasyonu için kullanılmıştır. Yüzey enerjisi ve akışkan viskoziteleri değiştirilerek, tek damlacıkların yüzeyler üzerindeki davranışı, bunların birleştirme mekanizması ve sınırlandırılmış kanallar içindeki denge şekilleri ve hareketleri sistematik olarak incelenmiştir. Damlacık daha viskoz bir akışkan içinde hareket ederse, damlacık hızının ıslanma gradyanına bağlılığının zayıfladığı gözlemlenmiştir. Büyük görünüm oranlı kanal akışları için, arayüz hareketinin iki boyutlu tahmininin üç boyutlu D3Q19 modeli hesaplamalarına yaklaştığı gösterilmiştir.

Keywords

• Arayüzey akışı
• Temas hattı
• Islanabilirlik gradyanı
• Lattice Boltzmann metodu

Self-Driving and Merging Droplets on Wettability Gradient Surfaces: A Lattice Boltzmann Study

Abstract

Self-transport and control of droplets play an essential role in the development of microfluidic devices, self-cleaning, water harvesting, and heat transfer enhancement. Droplet manipulation without an external force can be accomplished if a wetting gradient is structured on surfaces. The contact angle hysteresis generates a driving force toward the more wetting side. If this force is balanced by the viscous stresses near moving contact lines, droplets on such surfaces may attain constant translational speed determined by this balance. The D2Q9 lattice Boltzmann method is employed for the simulation of the self-driven droplets on wettability gradient surfaces. By varying the surface energy and fluid viscosities, the behavior of single droplets on surfaces, their merging mechanism, and equilibrium shapes and motions within confined channels are studied systematically. If the droplet moves in a more viscous fluid, the droplet’s speed dependence on the wetting gradient is observed to weaken. For large aspect ratio channel flows, it is shown that two-dimensional prediction of the interface motion approaches the three-dimensional D3Q19 model computations.

Keywords

• Interfacial flow
• Contact line
• Wettability gradient
• Lattice Boltzmann method

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