Abstract
In this paper, a novel two-stage dish concentrator (TSD) with a rotary secondary mirror (SM) is presented for solar thermal water/CO2 splitting. An in-house code for ray-tracing simulation of the concentrator was developed and validated. Among all feasible geometries, a hyperboloid with an upper sheet is the most popular option and is widely used as a secondary reflector, which is mainly discussed here. All para-hyperboloid geometric combinations can be categorized into three typical patterns (φ1 < π/2, φ1 = π/2, φ1 > π/2, φ1 = field angle of PM). The initial designs of the TSD, respective to different off-axis levels for each combination, were first designed. Then a new mathematical model was introduced to reshape the SM to reach optimal truncated designs. Finally, a new concept of an off-axis primary mirror (PM) combined with the truncated SM was evaluated by using the in-house ray-tracing code. The results include the optical efficiency, concentration ratio and intercepted radiant flux. The best solutions with the highest optical efficiency fall in the range π/2 ≤ φ1 ≤ (π − arcsin 0.8) rads and 0.4 ≤ NA2 ≤ 0.6 (NA2 = sin φ2, φ2 = field angle of SM), which vary with the concentration ratio and inclination angle.
Highlights
Concentrating solar thermal (CST) energy can be used to produce solar fuels through thermochemical processes for industrial, agricultural and other uses [1,2]
The rotating operation concept was initially proven by [27], in which a flat reflector was used as the secondary mirror (SM) In this paper, we introduce an improved concept of a two-stage dish concentrator (TSD) prototype with a rotatory hyperboloid SM
A novel concept of a paraboloidal dish combined with an off-axis hyperboloidal reflector was
Summary
Concentrating solar thermal (CST) energy can be used to produce solar fuels through thermochemical processes for industrial, agricultural and other uses [1,2]. For the first step (Equation (1)), the metal oxide is reduced at a relatively high temperature (Thigh ), usually above. Considering that a reactor should preferably have a minimum number of moving parts to avoid potential machine failures in such a high-temperature condition [26], a novel concept of TSD with a rotatory SM is proposed here for achieving successive water/CO2 splitting processes. The rotating operation concept was initially proven by [27], in which a flat reflector was used as the SM In this paper, we introduce an improved concept of a TSD prototype with a rotatory hyperboloid SM and evaluate its optical performance, including optical efficiency and concentration ratio, with respect to different geometric parameters including rim angle of primary mirror (PM) and SM and inclination angle of SM. The results can guide research for designing a novel solar dish cavity receiver–reactor (CRR) system
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