In this paper, visual experiments were carried out to study the NaCl crystallization process in acoustically levitated droplets. Image processing was employed to acquire the evaporation rate of the droplets and PIV analysis was used to characterize the flow filed. Effects of droplet size and initial NaCl concentration were investigated, and the crystallization behaviors in the levitated droplet and surface droplet were compared. The results indicate that the acoustic filed introduced a forced convection of fluid within the levitated droplets, influencing the evaporation rate, supersaturation degree and the morphology of the crystal product. The obtained mechanism is important to the application of acoustically levitated droplet and can be further applied to other crystallization research based on the acoustic levitation systems.
KEYWORDS: Fiber Bragg gratings, Porosity, 3D metrology, Temperature metrology, Solar energy, Sensors, Receivers, Temperature distribution, Reflection, Detector arrays
This study introduces a novel method for in-situ temperature measurement within photothermal porous materials for solar-driven interfacial evaporation. By embedding fiber Bragg gratings (FBGs) sensor arrays into the solar receiver constructed via a PDMS-CNPs sponge, 3D temperature distribution within the porous structure was reconstructed. Effects of the input light intensity and different working modes on the dynamic temperature response and the heat transfer characteristics were investigated. The results reveal that a thermal equilibrium could be quickly established within the photothermal porous material, and the heat loss to the bulk fluid could be significantly reduced by heat insulation configurations. The results highlight the effectiveness of the proposed method in in-situ temperature field monitoring for photothermal porous materials, which can be further applied in solar receiver construction and optimization of the solar evaporator for solar-driven interfacial applications.
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