Understanding the enhancement mechanism of critical electric field strength for salt-laden droplets electric coalescence through synchronous coupled magnetic field

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.