Session: 05-04 Solar Receiver Design 2

Paper Number: 108401

108401 - Investigation on a Double-Pass Tubular Absorber for Application in Solar Towers 

The central tower system is a member of concentrating solar power (CSP) family, in which the focused flux is collected on a central receiver with usually a billboard design. In conventional designs, a panel of parallel tubes is employed to absorb the high and non-uniform heat flux and heat the heat transfer fluid (HTF) for energy generation purposes. One of the challenges in this technology is the limited heat transfer rate between the solar absorber and the HTF, which usually requires an extra efficiency-enhancer to be compensated. In this regard, the present study combines the concept of double-pass flows with high-temperature solar receivers, introducing a novel tubular design to reduce heat loss and increase performance. The tubular modulus consists of two concentric tubes where the inner tube is open-ended and the outer tube is one-ended with a round closed ending, as well as several fins connecting the inner and the outer tubes. Thus, the concentrated heat is applied to the wall of the outer tube and conducted to the inner tube through the bypass walls. The HTF enters from the inlet of the inner tube, being preheated as runs along the tube axis. Since the length of the two tubes is equal, as the fluid exists to form the outlet of the inner tube, it reaches the closed end of the outer tube and splits to the annular space between the inner wall of the outer tube and the outer wall of the inner tube. When the second pass flow is formed in a reverse direction, the preheated HTF receives a higher heat flux with respect to the first pass and this keeps the large temperature gradient between the wall and HTF. To assess the effectiveness of such a design, a numerical study was performed using CFD analysis with Star CCM+ commercial software. Several simulations were made based on the thermal models, validated with experimental data for a solar furnace tested during an experimental campaign in June 2022. The thermo-hydraulic characteristics were analyzed for various solar fluxes (50, 100, and 200 kW/m²) and air mass flow rates (30, 40, 50 Lit/min) to provide a comprehensive comparison between the conventional smooth tubes and the proposed double-pass tubes. Numerical results suggested that for the peak solar flux of 50 kW/m² and a mass flow rate of 30 Lit/min, the double-pass design improves the energy efficiency by more than 30% compared to the identical smooth pipe design, while the pressure drop is 140% higher. As a result, the proposed design can be used as an alternative for future solar tower designs, bringing higher heat removal efficiency and decreasing the current Levelized Cost of heat and electricity of CSP systems.   

Presenting Author: Hossein Ebadi Dipartimento Energia "Galileo Ferraris", Politecnico di Torino

Presenting Author Biography: Hossein is a Ph.D. student enrolled in the Energy Department at Politecnico di Torino. He joined the MAHTEP research group in 2020, working on the development of highly efficient receivers for solar high-temperature systems. Based on his experience in teaching and research at Shiraz University, he has expertise in solar energy engineering including process simulation (heat and mass transfer) and applied thermodynamics for modeling, designing, and test of solar collectors for residential and agricultural applications. After joining PoliTo, he is working on numerical simulations using CFD analysis in the field of concentrating tubular receivers with a special interest in non-imaging concentrators. His latest research revolves around the application and optimization of a novel porous medium for CSP plants, operating with gaseous fluid at high temperatures.