Evaluation of heat transfer correlations based on input parameters in a solar parabolic trough collector using supercritical carbon dioxide

Concentrating Solar Power (CSP) technologies have emerged as leaders in generating renewable power. Parabolic trough collector (PTC) is the most widely used CSP technology for various applications of solar thermal heat at commercial level. Altering the heat transfer fluid (HTF) to supercritical CO2 (s-CO2) holds promise in improving the efficiency and operations of solar PTC. The present study discusses heat transfer correlations from literature for the horizontal flow in smooth tubes. The correlations have been evaluated for their suitability to predict the average Nusselt numbers by s-CO2 as the HTF in a solar PTC. Nusselt Numbers computed using these correlations have been compared with the validated numerical simulation. Utilizing a previously validated nonuniform solar heat flux as input for the three-dimensional finite volume method, the numerical thermal simulations were performed These correlations have been compared for the operating boundary range of the solar PTC. The impact of each thermophysical input parameter of HTF is outlined in the study. Additionally, a novel correlation is proposed based on the multiple regression of thermophysical input properties of the s-CO2 as HTF in the solar PTC. The proposed correlation based on input parameters has very high prediction accuracy. It can simplify the design analysis of the solar PTC field for the s-CO2.