Thermo-Fluid Characteristics of a Flat-Plate Collector with Different Riser Tube Configurations Employing ZnO/Water Nanofluids: An Experimental and Numerical Analysis

This work presents a comprehensive experimental and computational investigation into the thermo-fluid performance of a flat-plate solar collector featuring both wavy and straight risers, utilizing ZnO/water nanofluids under laminar flow regimes. The study is conducted at a low mass flow rate of 0.008 kg/s with two distinct concentrations of nanofluids. A three-dimensional, two-phase Eulerian model with an implicit formulation simulates the nanofluid flow through risers. Experimental results indicate that maximum enhancements in energy efficiency of 17.37% and 8.31% can be achieved with 0.2 and 0.4 mass fractions of ZnO/water nanofluids, respectively, relative to pure water. At 0.2 mass fraction of nanofluid, numerical findings claim an increase in efficiency of 6.86% and 20.03% for water- and nanofluid-based wavy riser collectors, respectively, compared to the water-based straight riser collector. Furthermore, the Nusselt number shows overall increments of 7.96% and 24.32% for the wavy riser collector with water and 0.2 mass fraction of ZnO/water nanofluid, respectively. Correspondingly, the Darcy friction factor exhibits 5.01% and 19.26% enhancements. These findings underscore the potential benefits of using wavy riser configurations and ZnO/water nanofluids to improve the thermal efficiency of flat-plate solar collectors.