Mofan Li,Donghai Yang,Lei Tian,Haotian Liu,Liangyu Cai,Limin He
Combining a magnetic field with an electric field offers a promising approach for enhancing oil–water separation, yet its underlying mechanisms are not fully understood. We systematically investigated the dynamic deformation of salt-containing water droplet suspended in oil under an electric–magnetic coupling field. Integrating high-speed camera experiments with molecular dynamics simulations, we found that the dynamic response amplitude of droplet is reduced compared to a single electric field. Our analysis suggests that ions deflect under electric–magnetic coupling, affecting ion enrichment and water molecule polarization, thereby weakening droplet tip charge and induced electric forces, which suppresses droplet deformation. Increasing the electric capillary number and ion concentration enhances suppression, whereas improving the electric field frequency to 500 Hz almost eliminates this suppression effect. Notably, the degree of droplet deformation inhibition remains consistent across different viscosity ratios. These research findings offer insights for designing dehydrators to intensify oil–water separation.
Mofan Li,Donghai Yang,Shiyi Lv,Xinming Zhao,Jianwei Wang,Minmin Xia,Limin He
Electric field-based synchronous coupling with magnetic fields has shown great potential in enhancing the efficiency of electric dehydration for crude oil. However, the mechanisms underlying electric-magnetic coupling and its influence on droplet coalescence are not yet entirely understood. This study aims to investigate the coalescence dynamics of salt-laden water droplets in oil under an electric-magnetic coupling field. Experimental investigations using high-speed cameras and simulations employing electrohydrodynamic/molecular dynamic methods were conducted to elucidate differences in critical coalescence conditions. The results revealed a significantly higher critical electric field strength required for droplet coalescence under the influence of an electric-magnetic coupling field compared to a single electric field. This behavior can be attributed to changes in the migration direction and aggregation region of ions caused by the electric-magnetic coupling effect. Consequently, the charge at the end of droplets decreases, and the weight of the electric field force competes with the capillary force, thereby hindering coalescence. Furthermore, the study revealed that at an ion concentration of 1000 mg·L −1 , the critical electric field strength exhibited a maximum enhancement rate of 18.2 %. This enhancement can be attributed to the combined effect of ionic migration, which becomes more pronounced at higher concentrations, and the influence on the polarization of water molecules. However, when the electric field frequency was increased to 500 Hz, the migration of ions was shortened, resulting in a significantly reduced enhancement rate of only 0.909 %. Finally, the mathematical relationships between the coupled magnetic field reinforced critical electric field strength for different control parameters were determined by fitting the data points. In summary, this study provides novel scientific insights into the deep dehydration of crude oil by investigating the effects of electric-magnetic coupling on droplet coalescence. The findings present valuable guidance for optimizing the efficiency of dehydration processes and ensuring the safe and stable production in oil industrial applications.
Icing of seawater droplets is capable of causing catastrophic damage to vessels, buildings, and human life, yet it also holds great potential for enhancing applications such as droplet-based freeze desalination and anti-icing of sea sprays. While large-scale sea ice growth has been investigated for decades, the icing features of small salty droplets remain poorly understood. Here, we demonstrate that salty droplet icing is governed by salt rejection-accompanied ice crystal growth, resulting in freezing dynamics different from pure water. Aided by the observation of brine films emerging on top of frozen salty droplets, we propose a universal definition of freezing duration to quantify the icing rate of droplets having varying salt concentrations. Furthermore, we show that the morphology of frozen salty droplets is governed by ice crystals that sprout from the bottom of the brine film. These crystals grow until they pierce the free interface, which we term ice sprouting. We reveal that ice sprouting is controlled by condensation at the brine film free interface, a mechanism validated through molecular dynamics simulations. Our findings shed light on the distinct physics that govern salty droplet icing, knowledge that is essential for the development of related technologies.
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