Hybrid optical and thermal simulation and experimental evaluation of linear fresnel receivers with single and dual non-vacuum tubes

Non-vacuum linear Fresnel receivers with secondary reflectors are prone to considerable convective and radiative heat losses, while experimental evaluation remains costly and time-consuming. This study develops a hybrid numerical methodology that combines Monte Carlo Ray-Tracing (MCRT) for optical analysis and Computational Fluid Dynamics (CFD) for thermal modelling, validated against experimental measurements on a single-tube receiver operated up to approximately 320 °C. The comparison shows excellent agreement, with deviations below 5% in global heat loss predictions, supporting the ability of the model to reproduce the overall heat balance of the reference configuration. The validated approach is then applied to assess and compare single- and dual-absorber tube designs integrated within a CPC-type cavity. Both designs achieve similar optical efficiencies (around 65%), while the dual-tube configuration is predicted to yield slightly lower overall heat loss coefficients (4.6-10.3 vs. 4.9-10.8 W/m²·K) over absorber tube temperatures ranging from 173 to 473 °C. Under the modelling assumptions and boundary conditions considered, this trend is associated with the greater spacing between the smaller-diameter tubes and the glass cover, which may mitigate radiative and convective heat losses to the ambient. Overall, The results suggest that the dual-tube configuration can offer a modest thermal advantage without significantly affecting optical efficiency. The proposed hybrid modelling approach provides a reliable and cost-effective alternative to extensive experimental testing for the comparative assessment and optimization of non-vacuum Fresnel receivers.