Improving the performance of large-aperture parabolic trough solar concentrator using semi-circular absorber tube with external fin and flat-plate radiation shield

An improved absorber tube (AT) design consisting of a semi-circular and an external flat fin with a flat-plate radiation shield inside an evacuated annulus is proposed for large aperture parabolic trough concentrator (PTC) systems. In the present design, the AT's semi-circular part absorbs the most sun rays. The other rays originally absorbed by the AT's upper part is intercepted by the external two fins. The flat-plate radiation shield reflects the external radiation energy from the AT's upper half back to the AT. The trough has an aperture of 8m and an 80° half rim angle. The AT consists of a semicircle with a diameter of 100 mm and outer fins. The optical and thermal efficiency of this new design was up to 83.3% and 80.3%, respectively. The optical and thermal efficiency was 8%-units higher than that of the traditional optimal design. The maximum temperature always appears at the edge of the fin, which is up to 50 °C higher than that of the heat transfer fluid (HTF) at 0.5 m/s, which was the optimal fluid rate for the new design. The fins also contribute to the efficiency of the PTC: 6.5% to the optical and over 3.5% to the thermal efficiency. The improved AT design will help to plan more effective PTC systems.