Comprehensive thermoparametric analysis of supercritical carbon dioxide in parabolic trough solar collector via an innovative method

The transition towards third-generation concentrated solar power (CSP) systems necessitates advanced working fluids, with supercritical carbon dioxide (sCO₂) emerging as a prime candidate. This study employed a rarely used discretised 1-D mathematical model to thoroughly explore and parametrically analyse the performance of sCO₂ in a parabolic trough solar collector (PTSC), marking an innovative application of this approach. The research method involves an unprecedented comprehensive parametric exploration of the thermodynamic relationships between various inlet and outlet temperatures, mass flow rates, and the lengths of the parabolic trough solar collector. Key findings include each inlet temperature's unique optimal performance parameters, necessitating precise optimisation for each target outlet temperature to suit different applications, which contradicts previous findings. Notably, thermal efficiency peaks at lower inlet temperatures with higher flow rates, though excessively high flow rates increase pumping power demands and capping efficiency. In addition, efficiency decreases with increased tube length due to heat loss and a reduced heat transfer temperature differential. Under variable outlet temperature conditions, the optimal exergetic efficiency was achieved with inlet temperatures ranging from 550 K to 800 K, with energetic efficiency consistently showed highest values at an inlet temperature of 350 K. However, when the outlet temperature is fixed, the inlet temperature that produces optimal exergetic efficiency varies considerably depending on the target outlet temperature and length, an insight that represents a significant advancement in the current literature. Remarkably, a 50 m PTSC length demonstrated the highest thermal and exergetic efficiency for fixed outlet temperature scenarios, with 86.07 % and 49.45 %, respectively. Moreover, the study identifies a turning point for thermal efficiency as DNI decreases, with efficiency peaking at low inlet temperatures and flow rates before declining. Exergetic efficiency generally decreases with lower DNI due to irreversibilities. To conclude, a design flowchart for integrating sCO₂ Brayton cycles with PTSCs is presented, offering a framework that can be applied in future research and development. These findings and designs provide new and comprehensive insights on PTSC performance that will be the basis for future designs, optimisations and innovations.