RSM-Based Empirical Modeling and Thermodynamic Analysis of a Solar Flat Plate Collector with Diverse Nanofluids

As the energy demand for household applications is increasing, the utilization of solar energy becomes important in fulfilling the energy needs of electrical and thermal appliances. Harvesting the energy from solar through solar thermal energy systems will be effectively used in household and industrial heating applications where the consumption of electrical energy is predominant. Solar thermal energy is harvested through simple devices like flat plate collectors but involves many challenges. Solar flat plate collectors’ thermal efficiency is improved by increasing the heat transfer rate by replacing the regular fluids with nanofluids due to their superior thermo-physical properties. Investigators are driven to find novel energy and exergy analysis by the challenges in effective heat transfer and conservation by improving it by including gold, alumina, and copper oxide nanoparticles. To investigate the energy efficiency characteristics of solar flat plate collectors (FPC), the experiments are carried out by considering the different nanofluids (nanofluids with nanomaterials such as gold (Au) and aluminum oxide (Al₂O₃) as well as copper oxide (CuO) as thermal transport media), flow rates of nanofluids (0.016 kg/s, 0.033 kg/s, and 0.05 kg/s), and with mass fraction of nanoparticles (0%, 0.1%, 0.2%, 0.3%, and 0.4%) in nanofluids as variables, such that the energy efficiency, exergy destruction, second law efficiency, entropy generation, and pressure drop performance indicators. The maximum exergy efficiencies are found with \(Au\) $\mathit{Au}$ nanofluids 31.55% and 28.78% at 0.4% mass concentration, which has the enhanced second law efficiency compared to water and other nanofluids. At the same time, exergy destruction is found to be minimum (1183.41 W) for \(Au\) $\mathit{Au}$ nanoparticle with 0.4% mass fraction and 0.016 kg/min flow rate. The maximum exergy destruction (1509.95 W) was found in the water with 0% concentration at 0.05 kg/min due to the minimum temperature and base fluid heat flow. The energy efficiency and second law efficiencies are well increased with a slight increase in the pressure drop for the 0.4% mass fraction of Au with Al2O3 and CuO nanoparticles. The DoE-based statistical method, the Box-Behnken method, is employed as an experimental design matrix to develop prediction models for exergy responses and pressure drop characteristics. The models are validated through ANOVA results and verified for the R² and R²_adj values (> 0.95), and the results are obtained from the models. The results of prediction models are found to have a good correlation with experimental results, and the maximum error between the prediction results and the experimental results is less than 5%. As a future scope, the models are suggested for optimizing the process variables to improve energy efficiency, exergy destruction, and pressure drop objectives.