Evaporative characteristics of sessile nanofluid droplet on micro-structured heated surface

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.

Effect of Nanoparticle Addition on Evaporation of Jet Fuel Liquid Films and Nanoparticle Deposition Patterns during Evaporation

Jet fuel-based nanofluid fuel has been proposed for improving the energy density and utilization efficiency of jet fuel that is widely applied in aircraft powered by aviation turbine engines. To recognize the evaporation behavior of the formed liquid film as a jet fuel-based nanofluid sprayed onto the engine wall or blades, this paper presents the evaporation and deposition characteristics of the jet fuel-based nanofluid liquid film adhering on the hydrophilic substrate. The changes in contact line, contact angle, volume, and deposition pattern during liquid film evaporation under different substrate temperatures, different nanoparticle concentrations, and different kinds of nanoparticle additions were investigated. The effect of nano-Al addition on the evaporation kinetics and deposition pattern of the nano-Al/jet fuel (nAl/JF) nanofluid fuel liquid film was explored. Repeated pinning and de-pinning of contact lines during evaporation occurred, resulting in the formation of concentric multi-ring deposition patterns. The addition of nano-Al increased the evaporation rate and shortened the evaporation lifetime, demonstrating a promotion effect on jet fuel liquid film evaporation. The existence of an energy barrier shows that the movement of three-phase contact lines on the hydrophilic solid surface presented not a continuous sliding behavior but a "stick-slip" behavior, and there were multiple jumps in contact lines and contact angles. Finally, a comparison was made with the deposition pattern of jet fuel liquid films with different graphite and Fe nanoparticle additions during evaporation. The mechanism of deposition phenomena was deeply revealed by the analysis of capillary flow and Marangoni recirculation.