Amir Momeni Dolatabadi, Marta Zocca, Giuseppe Petruccelli, Aki Grönman, Teemu Turunen-Saaresti
Thermal Energy Storage (TES) enables Concentrating Solar Power (CSP) plants to store collected solar heat for later use, ensuring continuous power generation even when sunlight is unavailable, enhancing operational flexibility and supporting a reliable renewable power supply. In advanced CSP cycles, supercritical carbon dioxide (sCO 2 ) has emerged as a promising working fluid owing to its non-toxic nature and superior thermophysical properties compared to air or steam. However, the pseudo-boiling phenomenon in sCO 2 can lead to the formation of vapor-like layers within tubular solar receivers, which significantly alter their thermal-hydraulic performance (THP). Recognizing that receiver THP can impact TES charging efficiency, this work focuses on modeling and analyzing flow and heat transfer under varying solar flux profiles, accounting for diurnal variations of the solar input. A dataset of 400 steady-state simulations was generated for two receiver types, namely solar power towers (SPT) and parabolic trough solar collectors (PTSC), using a 3D Eulerian approach with the SST turbulence model and a modified turbulent Prandtl number correlation validated against experiments. Operating conditions included pressures from 7.4 to 20 MPa, heat fluxes of 100 and 300 kW/m 2 , mass flux of 1001.5 kg/(m 2 ·s), and non-uniform axial solar flux distributions described by a Gaussian-based function, where parameter from 0.1 to controls the spread of the flux over the receiver surface. Results show that vapor-like layers can alter THP by up to 30%, shifting the operating pressure range for maximum heat transfer and causing performance deterioration when layer thickening occurs, markedly affecting solar receiver operation under realistic operating conditions. Contrary to common expectations, the highest THP in solar receivers has been observed in the presence of a thin vapor-like layer.