CFD analysis of a CPC structure for LFC applications

In the context of Concentrated Solar Power (CSP), the Linear Fresnel Collector (LFC) system is a promising and reliable technology. In this document, a detailed study is conducted, with the aim to assess the performances of a LFC receiver unit, in several environmental scenarios, and in a wide range of temperature. The receiver unit encompasses an absorber tube and a compound parabolic concentrator (CPC), designed to insulate the environment around the tube. Multiple CFD simulations are describing in detail the behaviour of the system by means of a 2D model, that solves the energy balance between the receiver and the coolant (external air). The 2D model requires an accurate computational fluid dynamic (CFD) analysis, implemented on the commercial STAR-CCM+ software, with the goal to determine the useful heat transferred to the external air, and the convective and radiative heat losses as a function of the temperature. This simplified 2D model requires accurate boundary conditions, including the thermal driver, which in this case, is represented by the fixed external temperature of the absorber tube, simulating the solar heat flux provided by Fresnel lens. External factors, as the presence of wind, are taken into account. The influence of the latter is a crucial factor to compute a complete analysis of the model, thus the system is simulated at several wind speeds. The model is deployed in a wide range of temperature (200-500 °C), providing different sights on the possible working fluids which are allowed to be used; molten salt mixture (60\%wt. NaNO3 + 40\%wt. KNO3), working in the temperature range 290-500 °C , and two diathermic oils (Therminol VP-1 and DelcoTerm Solar E15), respectively working in the temperature range 290-400 ℃ and 200-300 ℃. The heat losses evaluation, following the radial direction, gives an outlook of the performance of the receiver unit, and puts attention on the radiative and convective relative share and weight. The final aim of the project is to understand if the design of the new introduced CPC is competitive with other previous, and to develope a new correlation suitable for the adopted geometry.