In this achievement, we have studied the propulsion effects during nanosecond pulsed laser ablation in liquids. The studied effects are important for diversity of applications, including under liquid laser processing, laser shock peening, nanoparticle generation, laser-induced forward transfer, and different laser biomedical applications. The propulsion effects were investigated for different shapes of a blind hole filled with different volumes of water. To measure the gained momentum and the mechanical energy, the blind holes were drilled into the front surface of an aluminum rod that formed a ballistic pendulum. The ablated water and the propelled rod were monitored using a high-speed camera. The optical energy of laser radiation is transferred into the mechanical energy of the ablated liquid and the mechanical energy of the propelled solid. Using the conservation of linear momentum, we also estimated the share of the mechanical energy, carried by the propelled solid, since this part of the mechanical energy is particularly important for laser propulsion.
COBISS.SI-ID: 17026587
In this paper, we have studied the ability of laser surface engineering to produce surfaces that enable control and enhancement of a heat transfer by nucleate boiling of ethanol-water mixtures. The nucleate pool boiling experiments were performed on plain and five laser-textured stainless-steel foils using saturated pure water, 100% ethanol, 0.4% and 4.2% mole fraction ethanol - water mixtures. All laser-textured samples contained untreated, smooth 0.5 mm wide regions and intermediate textured surfaces, that differ in the width of the laser patterned regions (from 0.5 mm to 2.5 mm). For smooth surfaces, we measured significant decreases in average heat transfer coefficients (HTC) and increases in bubble activation temperatures in comparison with the laser-textured surfaces for all the tested working fluids. Significant enhancement in HTC (280%) on a textured heating surface with 2.5-mm-wide laser pattern was recorded using pure water. For pure ethanol, the highest enhancement of 268% was achieved on a heating surface with 1.5-mm-wide laser pattern. The highest enhancement of HTC for the tested binary mixtures was obtained using 2.0-mm wide-laser-textured regions (HTC improved by 235% and 279% for the 0.4% and 4.2% mixtures, respectively). Our results indicate that laser texturing can significantly improve boiling performance when the intervals of the laser-textured patterns are close to the capillary lengths of the tested fluids.
COBISS.SI-ID: 16891675
In this paper, we have studied how laser texturing by nanosecond fiber laser influences steel-surface wettability and corrosion resistance, when the surface is exposed to the atmospheric air or coated by a thin film of polymer. The surfaces were textured by different laser parameters. Some of them were kept uncoated, by the others were coated with epoxy or FAS (fluoroalkylsilane)-TiO2/epoxy. A comparative study was performed on samples kept under ambient conditions and in reduced air pressure and humidity. The results show the ability to induce wettability conversion from initially superhydrophilic to final superhydrophobic state either indirectly by ageing the uncoated laser-textured surface or directly by application of FAS-TiO2/epoxy coating. The storage conditions significantly influenced the wettability development of uncoated laser-textured steel. The process of ageing was slowed down in reduced air pressure and humidity. Detailed surface chemical analysis revealed that adsorption of the organic matters from the surrounding media influences the wettability conversion and ageing. However, the ageing of the coated surfaces was not affected by the storage conditions. Corrosion stability of uncoated laser-textured surfaces was enhanced over time due to the wettability transition, depending on their morphology. Coatings represent a superior barrier over the texture and wettability with the stable long-term surface protection against aggressive media.
COBISS.SI-ID: 1510570