Yunus Tansu Aksoy

This study examines droplet formation in ultrasonic spray coating (USSC) as a function of ink formulation (solvent, polymer, nanoparticles). First, acetone with polyvinylidene fluoride (PVDF) at concentrations from 0 to 4.5 wt.% is used to examine the effect of polymer additions. Additionally, acetone‐based SiO ₂ nanofluids (0–10 g/L), are explored. Finally, the combination of both polymer (PVDF) and nanoparticles (SiO ₂ ) in acetone is studied. Droplet sizes are measured using Phase Doppler Anemometry under varying atomization power and flow rates. Machine Learning (ML) algorithms are employed to develop droplet size models from key spray parameters, including atomization power, flow rate, polymer concentration, and nanoparticle concentration. The model shows significantly higher accuracy than existing empirical models. The model is further validated on IPA‐based inks with polyethylenimine (PEIE) or ZnO nanoparticles, and on acetone–cellulose acetate formulations, confirming its robustness across diverse ink systems. In addition to revealing the influence of coating parameters on the droplet formation and distribution, obtained both via experimental validation and ML, this study demonstrates that machine learning (ML) can be effectively applied to small experimental datasets, offering a robust framework for optimizing droplet formation and understanding key spray parameters in USSC for complex, unexplored inks enabling novel coating applications.

Nanofluids have long been explored for enhancing heat transfer, with early studies focusing primarily on improved thermal conductivity. However, in spray and droplet cooling applications, recent research indicates that conductivity alone cannot fully account for the observed performance gains. Additional mechanisms, such as Brownian-motion-induced convection, dynamic wetting, and nanoparticle-driven surface modification, significantly affect droplet impact dynamics, spreading behavior, boiling transitions, and transient heat transfer during impact and evaporation. This review critically synthesizes these effects, emphasizing how nanofluids interact with complex flow fields, steep thermal gradients, and heated substrates. It also examines emerging strategies for optimizing nanofluid design, including hybrid suspensions and phase-change-enhanced formulations. These developments open new avenues for high-efficiency cooling in electronics, renewable energy systems, and industrial spray processes. By moving beyond thermal conductivity as the sole performance metric, this review promotes a multi-scale, interdisciplinary framework for advancing nanofluid-based thermal technologies that align with sustainability, energy efficiency, and cost effectiveness.

Droplet impacting and freezing on solid surfaces are ubiquitous in nature and crucial to many industrial applications, while the underlying mechanism of this phenomenon remains elusive. In this paper, the effect of surface wettability on dynamic behaviors and freezing mechanism of a water droplet impacting on a solid substrate at a fixed Weber number of 200 has been experimentally investigated at various surface temperatures from −35.2 to −10 °C. With the decrease in temperature of the superhydrophobic surface, the complete rebound behavior moves to partial rebound and ultimately to full adhesion, mainly due to the competition between the fluid dynamics and heat transfer processes. An intense prompt splashing is achieved by altering the surface wettability toward superhydrophobicity. Raising the water repellency enhances the lift of the lamella rim during the initial droplet spreading. The receding velocity on superhydrophobic surfaces is about ten times larger than that on hydrophobic surfaces, while it is barely affected by the surface and droplet temperatures. Three distinct freezing shapes are observed in the experiments, namely, spherical ice, irregular ice, and central cap ice, and those can be explained through the analysis of the differences between the time for the onset of freezing and receding time. Some cases of droplet freezing after full receding, also known as spherical ice, include two freezing stages. First, the liquid–gas interface freezes within a short period. Next, the remaining liquid freezes upward because the evaporation through the liquid–gas interface leads to the temperature of this interface being lower than the liquid–surface interface temperature. A phase diagram described by the final equilibrium contact factor and the surface temperature reveals the conditions to form different freezing processes or to remain a liquid state.

The evolution of particle size is monitored in situ and in real-time during and after the sputtering of Ag atoms onto silicone oil using Light Extinction Spectroscopy. Aggregation and growth of nanoparticles occur both at the interface and inside the oil during and after the sputtering process.

Aggregation and growth of silver nanoparticles (Ag NPs) occur both at the plasma-liquid interface and inside the silicone oil during and after the magnetron sputtering. Despite the same amount of deposited silver, the growth kinetics of Ag NPs in silicone oil vary at different deposition rates. Stirring helps to disaggregate the particle lumps. The Light Extinction Spectroscopy (LES) technique is employed for the first time to in-situ and real-time characterize the particle size distribution (PSD) during and after the sputtering of the silver atoms onto silicone oil, i.e., Sputtering onto Liquids (SoL) process. The effects of the deposition rate and the stirring speed on the PSDs are analyzed. Based on De Brouckere mean diameters, the size evolution of Ag NPs over time is monitored. Via the LES technique, Ag NPs bigger than 20 nm are detected, and the PSDs are shown to be poly-disperse, which is also supported by the ex-situ TEM measurements and in-situ time-resolved absorption spectra. At higher deposition rates, larger NPs are formed. Faster stirring does not substantially influence the final size but promotes the formation of smaller NPs (<20 nm). Low colloidal stability of Ag NPs in silicone oil is also observed.