Comparative analysis of thermo-hydraulic performance in absorber tubes with small box inserts: impact of nanofluid integration

This study centers on improving the thermo-hydraulic efficiency of tube receivers within concentrated solar power (CSP) systems by employing small box inserts. Various heat transfer fluids are examined: Therminol VP1, water, ethylene glycol Al₂O₃ and CuO nanofluids. The aim is to compare the improvements in thermo-hydraulic performance achieved with these enhancements in the tube receiver. To analyze the effects of these modifications, Ansys FLUENT software and the RNG k-ε turbulence model are utilized. The key parameters examined include the Nusselt number, friction factor, and overall thermal performance. The findings are validated by comparing them with experimental and numerical results, thereby contributing to a deeper understanding of how to enhance the thermo-hydraulic performance of tube receivers in CSP systems. The final results of the study demonstrate a notable rise in the Nusselt number, with improvements of up to 53% and 12% observed for Therminol VP1 compared to the smooth tube with water and Al₂O₃ compared to CuO nanofluid, respectively. Additionally, the friction number is reduced by 1.8 and 2.35 times, respectively. Moreover, the use of Therminol VP1 nanofluid improves the thermo-hydraulic performance of heat transfer by up to 1.63 in the turbulent regime and up to 1 in the laminar regime flow. Other numerical results, such as the pressure drop and temperature gradient, are also examined and analyzed. This study adds to the body of knowledge on improving the thermo-hydraulic efficiency of tube receivers in CSP systems, furthering our understanding in this area.