Twisted tape inserts in parabolic trough solar collectors : assessment of energy, exergy, and environmental impacts

The parabolic trough solar collector is a solar technology extensively employed to focus and harness solar energy for diverse heating purposes. One effective technique to enhance its thermal performance involves the insertion of swirl generators within its absorber tube. In this research, experimental investigation on performance enhancement of parabolic trough solar collector using single twisted tape and dual twisted tape insert across Reynolds number values ranging from 1,000 to 9,000 is performed. Collector efficiency, Nusselt number, friction factor, performance improvement factor, and exergy efficiency are examined for single twisted tape inserts with pitch to width ratios (y/w) of 1, 1.5, 2, 2.5, and 3, and dual twisted tape inserts with y/y₀ ratios of 2, 3, and 4. Maximum enhancement in collector efficiency is reported at the lowest flow rate for both inserts. The single twisted tape insert with pitch to width ratio of 1 and the dual twisted tape insert with a pitch ratio of 2 exhibit the most notable enhancements in the evaluated performance parameters. Specifically, at lower flow rates (Re < 4400), the dual twisted tape insert (y/y₀ = 2) outperforms the single twisted tape insert (y/w = 1). This dual twisted tape insert configuration provides a thermal efficiency enhancement of 14 %, while the Nusselt number and friction factor enhancement are found to be 372 % and 1600 % compared to bare tube. Additionally, the exergy efficiency exhibits a peak increase of 20.8 % at the lowest flow rate using the dual twisted tape insert (y/y₀ = 2). This improvement translates to an annual CO₂ reduction between 1.53 tons/year offering a highest enviro-economic benefit of 22.19 US dollars per year.