Droplet freezing on cold superhydrophobic surfaces has been studied extensively in recent years. However, previous works are mainly focused on studying water droplet freezing behavior; little work has been conducted to investigate the freezing dynamics of nanofluid droplets on superhydrophobic surfaces. In this work, freezing morphologies of water and nanofluid droplets on superhydrophobic surfaces with different roughnesses were compared and studied. The nanofluid droplets underwent a shape transition from spherical to flat plateau morphology, different from the frozen water droplets that exhibit a sharp cusp. The size of the flat plateau for the frozen nanofluid droplet increases with increasing nanoparticle concentration. The underlying mechanism of the morphology change during the freezing process was elucidated using COMSOL Multiphysics. Compared to the frozen water droplets, more air bubbles are trapped inside the frozen nanofluid droplets, which might be ascribed to the fast freezing speed of the nanofluid droplets. These results can provide important insights for many applications that require freezing of nanofluid droplets, such as material solidification, three-dimensional (3D) printing, as well as phase change enhancement.

中文翻译：

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超疏水表面上纳米流体液滴的冻结

近年来，对冷超疏水表面上的液滴冻结进行了广泛的研究。但是，以前的工作主要集中在研究水滴的冻结行为。研究超疏水表面上的纳米流体液滴的冻结动力学的工作很少。在这项工作中，对具有不同粗糙度的超疏水表面上的水和纳米流体液滴的冻结形态进行了比较和研究。纳米流体小滴经历了从球形到平坦平台的形态转变，这与表现出尖锐尖端的冷冻水滴不同。冷冻的纳米流体液滴的平坦平台的尺寸随着纳米颗粒浓度的增加而增加。使用COMSOL Multiphysics阐明了冷冻过程中形态变化的潜在机制。与冷冻的水滴相比，更多的气泡被困在冷冻的纳米流体液滴内，这可能归因于纳米流体液滴的快速冷冻速度。这些结果可以为需要冻结纳米流体液滴的许多应用提供重要见解，例如材料固化，三维（3D）打印以及相变增强。