Ferrofluid droplet neck self-similar breakup behavior

doi:10.11949/0438-1157.20230564

Abstract

Abstract:

Control of the droplet generation process can be used to improve the efficiency of chemical processes such as mixing, extraction, and emulsification. This paper investigates the magnetic manipulation of ferrofluid droplet generation at the capillary in a liquid-liquid system. The continuous phase is dimethyl silicone oil with various viscosities, and the dispersed phase is a ferrofluid with a volume concentration of 3.6%. The study provides insight into the formation and breakup behavior of the ferrofluid droplet neck. We classified the different stages of droplet generation and analyzed the force processes: θ> 90°, the initial stage, where the interfacial tension dominates; θ< 90°, the necking stage, where the magnetic and viscous drag forces dominate. The magnetic force, viscous resistance and inertial force are dimensionless by interfacial tension. The changes of the limit length of the ferrofluid droplet, the thinning rate of the minimum neck diameter and its relative neck position under different magnetic Bond numbers, Weber numbers and Ohnesorge numbers are systematically studied. The results demonstrate that the droplet limiting length is inversely proportional to the magnetic force, proportional to the viscous drag, and independent of the inertial force (0.19 ≤ We ≤ 1.34). The minimum neck diameter thinning rate decreases with increasing viscous drag but is not affected by magnetic and inertial forces, exhibiting self-similar breakup behavior at different magnetic Bond and Weber numbers.

Key words: ferrofluid droplets, neck, self-similar behavior, two-phase flow, microfluidics, hydrodynamics

摘要：

对液滴生成过程的控制可用于提高混合、萃取以及乳化等化学过程的效率。研究了液-液系统中毛细管处磁液液滴的磁操控生成，以不同黏度的二甲基硅油作为连续相，体积分数为3.6%的铁磁流体作为分散相，针对磁液液滴颈部的形成和破裂行为进行了深入探讨。划分了液滴生成的不同阶段并分析了受力过程：θ > 90°，初始阶段，界面张力占主导；θ < 90°，缩颈阶段，磁力和黏性阻力占主导。以界面张力对磁力、黏性阻力以及惯性力进行无量纲化，系统研究了磁液液滴极限长度、最小颈部直径减薄速率及其相对颈部位置在不同磁Bond数、Weber数和Ohnesorge数下的变化。结果表明，液滴极限长度与磁力成反比，与黏性阻力成正比，不受惯性力（0.19 ≤ We ≤ 1.34）的影响。最小颈部直径减薄的速率随黏性阻力增大而降低，但不会受磁力和惯性力的影响，在不同磁Bond数和Weber数下呈现出自相似破裂行为。

关键词: 磁液液滴, 颈部, 自相似行为, 两相流, 微流体学, 流体动力学

CLC Number:

TQ 021

Xuanzhi HE, Yongqing HE, Guiye WEN, Feng JIAO. Ferrofluid droplet neck self-similar breakup behavior[J]. CIESC Journal, 2023, 74(7): 2889-2897.

何宣志, 何永清, 闻桂叶, 焦凤. 磁液液滴颈部自相似破裂行为[J]. 化工学报, 2023, 74(7): 2889-2897.

Figures/Tables 7

Fig.1 Schematic diagram of the experimental setup and magnetic field distribution

Fig.2 Definition of the ferrofluid droplet initial stage and necking stage and the force analysis of the two stages

Fig.3 Variation of forces during the ferrofluid droplet generation

Fig.4 Variation of dimensionless limiting length of ferrofluid droplets with magnetic Bond number

Fig.5 The definition of the ferrofluid droplet minimum neck diameter and its relative neck position

Fig.6 The variation of the dimensionless minimum neck diameter of the ferrofluid droplet and its corresponding relative neck position with the remaining time

Fig.7 Time series images of the variation of zneck' following τ during the necking stage

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