# Performance analysis of a direct-absorption parabolic trough solar collector

**Authors:** Caiyan Qin, Joong Bae Kim, Bong Jae Lee  
**arXiv:** [1810.08801](https://arxiv.org/abs/1810.08801)  
**Date:** 2018-10-20  
**Summary page:** https://www.summarizepaper.com/en/paper/1810.08801v1/

## Key points

- The study focuses on improving the efficiency of direct-absorption parabolic trough solar collectors (DAPTSC) for high-temperature industrial applications.
- DAPTSC using nanofluids shows 5-10% higher thermal efficiency than conventional surface-based parabolic trough solar collectors (SBPTSC) for inlet temperatures up to 250°C.
- Existing DAPTSCs with transparent inner tubes have limitations due to restricted optical path length, requiring a high absorption coefficient for nanofluids.
- An innovative approach of applying a reflective coating on the upper half of the inner tube outer surface in DAPTSC doubles the optical path length, allowing for a reduction in the absorption coefficient of nanofluids.
- Coated DAPTSC demonstrates advantages over transparent DAPTSC when the absorption coefficient is below 0.5 cm$^{-1}$ for receivers with a 7 cm inner tube diameter.
- Comparative analyses are conducted among transparent DAPTSC, coated DAPTSC, and SBPTSC with black chrome coating to explore optimal operational conditions such as inner tube diameter, flow rate, and inlet temperature.
- The study also investigates the impact of using a glass envelope for vacuum evacuation on different types of solar collectors.

## Summary

The study titled "Performance analysis of a direct-absorption parabolic trough solar collector" by Caiyan Qin, Joong Bae Kim, and Bong Jae Lee focuses on improving the efficiency of direct-absorption parabolic trough solar collectors (DAPTSC) for high-temperature industrial applications. The conventional surface-based parabolic trough solar collector (SBPTSC) faces limitations due to high radiation loss at high surface temperatures. To address this issue, DAPTSC using nanofluids has been proposed, showing a 5-10% higher thermal efficiency than SBPTSC for inlet temperatures up to 250°C. However, existing DAPTSCs have transparent inner tubes that restrict the optical path length of sun rays passing through the nanofluids. This limitation necessitates a high absorption coefficient for nanofluids, which can lead to particle agglomeration and negatively affect collector performance. In this research, an innovative approach is introduced by applying a reflective coating on the upper half of the inner tube outer surface in DAPTSC. This modification doubles the optical path length compared to transparent DAPTSC, allowing for a reduction in the absorption coefficient of nanofluids. The coated DAPTSC demonstrates significant advantages over its transparent counterpart when the absorption coefficient is below 0.5 cm$^{-1}$ for receivers with a 7 cm inner tube diameter. Furthermore, comparative analyses are conducted among transparent DAPTSC, coated DAPTSC, and SBPTSC with black chrome coating to explore optimal operational conditions such as inner tube diameter, flow rate, and inlet temperature. The study also investigates the impact of using a glass envelope for vacuum evacuation on these different types of solar collectors. Overall, this research contributes valuable insights into enhancing the performance and efficiency of direct-absorption parabolic trough solar collectors through innovative design modifications and operational optimizations.