Thermo-hydraulic and second-law performance assessment of MXene ionanofluids in flat-plate solar collectors

MXene-based ionanofluids are promising heat transfer fluids for solar thermal applications due to their superior thermophysical properties. This study evaluates their thermo-hydraulic and second-law performance in a flat-plate solar collector by integrating experimentally measured thermophysical properties with numerical simulations to identify the optimum operating conditions. To assess various parameters, including outlet temperature, surface temperature, heat transfer properties, pressure drop, pumping power, absorbed heat rate, energy efficiency, entropy generation, and performance index (PI), simulations were carried out over a practical inlet temperature range of 293.15–323.15 K and Reynolds numbers (Re) from 100 to 900. The numerical results demonstrate that MXene ionanofluids offer significant thermal enhancement with regulated hydraulic penalties. Thermal conductivity and specific heat capacity increase by roughly 53–54% and 16–17%, respectively, at 1 wt%, resulting in a heat transfer coefficient increase of up to 48–51% compared to the base fluid. When Re increases from 100 to 900, it can reduce the output temperature by up to 8.2% and enhance energy efficiency by roughly 111%. However, at higher nanoparticle concentrations, MXene incorporation reduced the pressure drop by up to 36%, thereby lowering the pumping power requirement. According to second-law analysis, system irreversibility is primarily due to thermal entropy generation, with frictional entropy accounting for less than 0.002% of the total. 0.2 wt% MXene ionanofluid is the ideal concentration, according to performance index analysis under equal pumping power settings, with PI values reaching 0.88 at 323.15 K. Overall, the study shows that MXene ionanofluids are attractive options for high-performance flat-plate solar thermal systems because they provide a good balance between heat-transfer improvement and hydraulic losses, especially at low concentrations.