Thermal-fluid analysis of a parabolic trough solar collector of a direct supercritical carbon dioxide Brayton cycle: A numerical study

Recently, supercritical carbon dioxide, S-CO2, has been suggested for utilization as the working fluid in solar thermal power plants. Replacing current working fluids with S-CO2, however, is not a straightforward task. This work numerically investigates the heat transfer and flow filed in a parabolic trough solar collector which carries S-CO2. A full-scale three-dimensional model of the parabolic trough is developed and analyzed using the Star CCM + software. The variation of carbon dioxide's thermophysical properties inside the receiver tube is considered. The computational model is validated against a set of experimental data published by Sandia National Laboratories with no more than a 2.81% error margin. The numerical experiment is carried out at five different times during a typical summer day in Albuquerque, NM. Numerical results confirm that in all cases, heat loss from the upper half of the receiver tube is more than the absorbed solar incidence on that side. At noon, when the absorbed heat flux on the lower surface of the receiver tube reaches its maximum at 29810 W/m2, the net heat loss flux from the upper half of the receiver tube reaches 2622 W/m2. Consequently, the heat transfer from the upper half of the receiver tube unfavorably impacts the thermal efficiency of the parabolic trough. Additionally, while from 8 AM to 12 PM thermal efficiency drops less than 2.4%, the S-CO2 temperature increment grows over 182%. A reverse trend occurs from noon to 4 PM, mainly due to the change in the available solar incidence.