We present a numerical model that describes the microfluidic generation and manipulation of ferrofluid droplets under an external magnetic field. We developed a numerical Computational Fluid Dynamics (CFD) analysis for predicting and optimizing continuous flow generation and processing of ferrofluid droplets with and without the presence of a permanent magnet. More specifically, we explore the dynamics of oil-based ferrofluid droplets within an aqueous continuous phase under an external inhomogeneous magnetic field. The developed model determines the effect of the magnetic field on the droplet generation, which is carried out in a flow-focusing geometry, and its sorting in T-junction channels. Three-channel depths (25 μm, 30 μm, and 40 μm) were investigated to study droplet deformation under magnetic forces. Among the three, the 30 μm channel depth showed the most consistent droplet production for the studied range of flow rates. Ferrofluids with different loadings of magnetic nanoparticles were used to observe the behavior for different ratios of magnetic and hydrodynamic forces. Our results show that the effect of these factors on droplet size and generation rate can be tuned and optimized to produce consistent droplet generation and sorting. This approach involves fully coupled magnetic-fluid mechanics models and can predict critical details of the process including droplet size, shape, trajectory, dispensing rate, and the perturbation of the fluid co-flow for different flow rates. The model enables better understanding of the physical phenomena involved in continuous droplet processing and allows efficient parametric analysis and optimization.

中文翻译：

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在微型装置中利用磁场形成和操纵铁磁流体液滴：数值参数研究。

我们提出了一个数值模型，描述了外部磁场下铁磁流体液滴的微流体生成和操纵。我们开发了数值计算流体动力学 (CFD) 分析，用于预测和优化在存在和不存在永磁体的情况下铁磁流体液滴的连续流动生成和处理。更具体地说，我们探索了外部不均匀磁场下水连续相内油基铁磁流体液滴的动力学。开发的模型确定了磁场对液滴生成的影响，液滴生成在流聚焦几何结构中进行，并在 T 形连接通道中进行分类。研究了三通道深度（25 μm、30 μm 和 40 μm），以研究磁力下的液滴变形。在这三者中，30 μm 的通道深度在研究的流速范围内显示出最一致的液滴产生。使用具有不同磁性纳米粒子负载的铁磁流体来观察不同磁力和流体动力比率的行为。我们的结果表明，可以调整和优化这些因素对液滴尺寸和生成速率的影响，以产生一致的液滴生成和分选。该方法涉及完全耦合的磁流体力学模型，可以预测过程的关键细节，包括液滴尺寸、形状、轨迹、分配速率以及不同流速下流体协流的扰动。该模型可以更好地理解连续液滴处理中涉及的物理现象，并可以进行有效的参数分析和优化。