Internal 3D temperature reconstruction of the photothermal porous materials for solar driven interfacial evaporation via FBG sensor array

Photothermal porous materials have been widely employed in solar-driven interfacial evaporation (SDIE) system as the core units of high-efficient evaporators. The temperature distribution within the porous matrix is crucially important to the overall performance solar evaporator. However, due to their opaque optical property and complex geometry, traditional probing methods such as thermography and thermocouple have been facing significant challenges in acquiring the internal temperature distribution of the photothermal porous evaporators. In this work, we proposed in-situ temperature distribution detecting strategy based on the fiber Bragg grating (FBG) sensors. The FBG sensing array was embedded into the photothermal porous evaporator with 3 detecting planes and total 27 detecting points. By using the FBG sensor array, the time-dependent internal temperature distribution of the solar evaporator was successfully reconstructed. The effects of incident light intensity, evaporator configuration on the internal thermal response were investigated. The results show that the increase of the light intensity could significantly lift the evaporation rate, the measured temperature fields confirmed the maximum surface temperature was increased by 28.5 °C as the incident light intensity risen from 70 mW/cm 2 to 130 mW/cm 2 . Additionally, the reconstructed temperature fields revealed heat transfer mechanism in different working modes of the solar evaporator. By introducing thermal insulation layer or using supporting structure to separate the evaporator and the bulk fluid, the vertical heat loss can be significantly reduced, the overall solar-to-vapor efficiency was increased by 16%. Finally, the proposed sensing strategy was validated in polymeric sponge, porous hydrogel, and biomass-derived carbon foam evaporators, demonstrating broad applicability to diverse photothermal porous materials. The present work introduces a novel experimental framework for direct visualization of internal thermal behavior in SDIE systems and provides inspiring insights for the rational design of high-performance solar evaporators.