The efficiency of solar thermal systems strongly depends on the heat transfer characteristics of absorber surfaces. Conventional coatings often exhibit poor wettability, leading to uneven liquid film formation, insulating vapour layers, and reduced thermal performance. This study investigates the application of super-hydrophilic surfaces to enhance heat transfer in solar thermal collectors. A tri-layer nanostructured coating composed of Zinc Oxide (ZnO), Cerium Oxide (CeO 2 ), and Graphene Oxide (GO) was developed using plasma treatment and chemical vapor deposition to achieve superior hydrophilicity. The coating demonstrated a contact angle of 10–13°, high surface roughness (260 nm), small particle size (12 nm), and large surface area (820 m 2 g −1 ), promoting efficient water-film formation and reduced thermal resistance. Heat transfer measurements revealed a maximum HTC of 410 W m −2 K −1 at 2.0 L min −1 , a collector efficiency of 76% at 900 W m −2 irradiance, and an annual energy gain of 610 kWh m −2 , representing 45% improvement over uncoated surfaces. Durability tests confirmed 1200 wear cycles, minimal UV degradation (7%), and 55% reduction in thermal resistance due to fouling mitigation. Ablation studies highlighted synergistic contributions from all three nanomaterials. Predictive modelling using RSM, ANN, CNN, and LSTM provided accurate optimization of coating parameters, with LSTM achieving R 2 = 0.99. These findings demonstrate that super-hydrophilic coatings significantly enhance thermal performance, stability, and long-term energy yield of solar collectors. Future research should focus on scaling up coatings, exploring alternative nanomaterials, and integrating with hybrid solar-thermal systems to further maximize operational efficiency and durability.
Barmavatu et al. (Sat,) studied this question.