Coupled thermal and optical analysis of a planar waveguide concentrator-receiver

Analysis and Optimization of a Novel Hexagonal Waveguide Concentrator for Solar Thermal Applications

“…From the Dittus-Boelter equation [30], the assumed convective heat transfer coefficient for thermal oil-based HTF flow in the receiver corresponds to a Reynolds number of~15,000, which is typically observed in solar thermal systems [42]. The value for absorptivity (β) of the receiver surface is considered as 0.95 [21,22]. The feasible design space for waveguide is dictated by the maximum allowable temperature in the waveguide due to irradiation absorption during operation.…”

“…Table 1. Thermophysical property of waveguide materials [21,43]. Figure 2 represents the temperature contours in a ZK7 hexagonal waveguide solar concentrator element at different T F and I 0 for t wg = 0.025 m, R r = 0.02 m, and L wg = 0.25 m. The maximum temperature within the waveguide is governed by volumetric heat generation rate, because of the incident solar irradiation absorption, HTF temperature that affects the heat exchange between the waveguide edge facing the HCE and the receiver pipe surface, and the heat loss to ambient in the form of convection and radiation (Equations ( 5) and ( 6)).…”

“…The optimization problems can be mathematically expressed as: max R r ,t wg,Lwg P o and min R r ,t wg,Lwg COH (subject to : T max − T c ≤ 0) (17) where T max is the maximum temperature in the waveguide that is obtained from the numerical model and T c is the maximum permissible waveguide temperature that is constrained by either the tensile strength constraint or the maximum operating temperature constraint. The maximum continuous operating temperature limit constrains the maximum permissible temperature for PC to T c = 86.3 • C, whereas the tensile strength constrains the maximum permissible temperature for ZK7 to T c = 120 • C [21,43]. The optimization problem that is presented in Equation ( 17) was solved using MATLAB by means of sequential quadratic programming [44], a nonlinear programming technique.…”

“…Nithyanandam et al [21] recently conducted a coupled optical and thermal analysis on a planar waveguide solar concentrator for CST applications. The study was further extended for the radial waveguide concentrator [22].…”