Investigation on a Double-Pass Tubular Absorber for Application in Solar Towers

The present study combines the concept of double-pass flows with high-temperature solar receivers, introducing a novel design to reduce heat losses and increase performance. A tubular absorber from the billboard solar tower systems was used to develop the new double-pass (DP) design, working with air as the heat transfer fluid. To assess the effectiveness of such a system, a numerical study was performed using CFD analysis with Star CCM+ commercial software. Several simulations were made based on the thermal models, validated with real data obtained from a solar furnace tested during an experimental campaign in June 2022. The thermo-hydraulic characteristics were analyzed for various solar peak fluxes (50, 100, and 200 kW/m2) and air mass flow rates (30, 40, 50 L/min) to provide a comprehensive comparison between the single pass (SP) and DP absorbers. The computed numerical results suggested that using the DP design instead of SP absorbers under all the test conditions, the average energy and exergy efficiency enhancement are 35% and 55%, respectively, while the pressure drop increases with an average of 62%. As a result, the DP design can be used as an alternative for future solar tower designs, bringing higher heat removal efficiency in air-based solar systems.