PERFORMANCE ENHANCEMENT OF FLAT-PLATE SOLAR COLLECTORS USING CeO2âWATER AND ZnO-WATER NANOFLUIDS AS ADVANCED HEAT TRANSFER FLUIDS

Among the various approaches, the use of nanofluids-suspensions of nanoparticles in base fluids-has emerged as an effective method for improving the thermal performance of solar collectors. Metal oxide nanoparticles, such as cerium oxide (CeO<sub>2</sub>) and zinc oxide (ZnO), have gained significant attention due to their high thermal conductivity, chemical stability, low cost, and environmental compatibility. The aim of this study is to evaluate and compare the thermal and exergetic performance of CeO<sub>2</sub>-water and ZnO-water nanofluids at varying volumetric concentrations (0.01%, 0.1%, and 1%) and flow rates (50, 150, and 250 L/h) in a flat-plate solar collector. Both experimental and numerical analyses (CFD) were conducted to assess parameters such as collector efficiency, temperature-irradiance-time behavior, entropy generation, and exergy destruction. The ZnO-water nanofluid at 1% concentration and 250 L/h flow rate yielded the highest thermal efficiency, showing a 28% improvement compared to water. In contrast, the CeO<sub>2</sub>-water nanofluid at 0.01% concentration and 50 L/h flow rate demonstrated only an 8% efficiency increase. The CFD results showed strong agreement with experimental data. The findings confirm that both CeO<sub>2</sub> and ZnO nanofluids enhance the thermal and exergetic performance of flat-plate solar collectors, with ZnO demonstrating superior efficiency due to its higher thermal conductivity.