Experimental investigation of a silicon nanoparticle-modified absorber coating for a flat-plate solar collector in agricultural drying

Solar drying can reduce dependence on conventional fossil-fuel-based thermal energy, but solar collector efficiency strongly influences performance. This study investigates whether modifying the absorber surface with silicon nanoparticles can improve the thermal performance of a FPSC and enhance agricultural drying. The study combines silicon-nanoparticle absorber modification, surface characterization, controlled air mass-flow optimization, and practical drying validation to evaluate the relationship between absorber characteristics, collector performance, and drying behavior. We prepared and compared three absorber coatings: BP, BP-3 wt% G, and BP-5 wt% Si. We conducted experiments at air mass flow rates of 0.3, 0.5, and 0.7 kg.s −1 and evaluated absorber temperature, solar irradiance, collector efficiency, and drying performance. SEM/EDS analysis confirmed the incorporation and distribution of silicon nanoparticles within the coating. The BP-Si coating achieved a maximum thermal efficiency of 25.8%, an improvement of 7.6 percentage points (41.8% relative improvement) over the conventional BP coating's 18.2% efficiency under the same operating conditions. The corresponding maximum absorber temperature reached approximately 125 °C. In the drying validation experiment, apple moisture content decreased from approximately 87% to 8%, with the BP-Si system achieving the target moisture in 23 h, compared with 30 h for BP-G and 33 h for BP. Statistical analysis showed that absorber coating composition, air mass flow rate and their interaction significantly affected collector thermal efficiency ( p < 0.01). Overall, the results demonstrate that silicon-nanoparticle modification of a conventional absorber can enhance collector thermal performance and reduce time without requiring complex collector modifications.