An investigation on the usage of different supercritical fluids in parabolic trough solar collector

The temperature limitation of thermal oil which limits the overall efficiency of a thermodynamic cycle has propelled the study of the usage of supercritical fluid in parabolic trough solar collector (PTSC) due to its ability to operate at higher temperature levels. sC0(2) is the most popular supercritical fluid currently studied in PTSC, but there are some other supercritical fluids have been used in industrial applications yet rarely studied in PTSC. In this research, the performance of three different supercritical fluids namely, water (sH(2)O), nitrogen (sN2); Sulphur hexafluoride (sSF(6)) along with carbon dioxide (sCO(2)) was studied and compared. A 1-D mathematical model was developed, validated, and it was solved by the commercial software EES. The results showed that the energetic performance of water is superior to the rest of the fluids at common inlet temperatures with sN(2) showing comparable performance to sCO(2) and sSF(6) showing consistently weaker performance than the rest. The exergetic performance of these fluids showed that sH(2)O and sSF(6) are promising alternatives to sCO(2). All fluids showed maximum exergetic efficiency at an inlet temperature of 750K with the respective maximum for sH(2)O, sSF(6), sCO(2) and sN(2) of 46.46%, 46.24%, 46.11% and 45.76%. Comparison of these supercritical fluids to Therminol VP-1 and molten salts also showed promising potential. H2O is the best supercritical fluid for usage in thermal storage at 650K where it has thermal storage energy density (TSED) of around 165% higher than the highest value of molten salt's TSED. (c) 2020 Elsevier Ltd. All rights reserved.