Magnetic regulation on evaporation behavior of ferrofluid sessile droplets

Active magnetic regulation is an emerging subject due to the special and programmable wettability of the sessile ferrofluid droplet. The interaction between liquid and externally applied magnetic field gives rise to controllable spreading and thus evaporation. This work reports the experimental and numerical results of the natural evaporation of a ferrofluid droplet under the effect of a nonuniform magnetic field. The evaporation process of droplets is described into two stages in terms of the geometric distortion and the appearance of the deposition pattern. The presence of the magnetic field leads to a transition of droplet drying from the disk shape with a ring to multiple peaks. A numerical model is established to simulate the evaporation process of ferrofluid droplets with the arbitrary Lagrangian-Eulerian method for tracking droplet deformation. The increasing magnetic flux could effectively enlarge the contact radius and enhance the internal flow of the ferrofluid droplet, thus promoting the evaporation process. The numerical results are verified by comparing the droplet geometry deformation with the experimental results. In both the numerical and experimental investigations, the externally applied magnetic field shortens the process of ferrofluid droplet evaporation. The design and optimization of the magnetic field play an important role in regulating ferrofluid droplet evaporation, which in turn facilitates technological advances in industries such as evaporative cooling and inkjet printing.

Automated summary

Active magnetic regulation is an emerging field that focuses on the controllability of ferrofluid droplet spreading and evaporation. The interaction between the liquid and externally applied magnetic field alters the drying process, resulting in a transition from disk-shaped to peak-filled droplets. A numerical model based on the arbitrary Lagrangian-Eulerian method is used to simulate the deformation and evaporation of the droplets, showing that increasing magnetic flux enhances the contact radius and internal flow, thereby promoting the evaporation process. The experimental and numerical investigations both confirm that the externally applied magnetic field accelerates the evaporation process of ferrofluid droplets. The design and optimization of the magnetic field are crucial for regulating droplet evaporation, benefiting industries such as evaporative cooling and inkjet printing.