Thermal and enviro-economic evaluation of a compound parabolic collector enhanced with Al2O3-water nanofluid and dual twisted inserts

Abstract

Compound parabolic collectors (CPCs) are potential solar thermal systems, but their performance is usually limited by restricted convective heat transfer within the absorber tube. Although nanofluids and internal inserts have been investigated individually, few efforts have been directed toward their combined use in CPCs. This experiment explores the synergistic effect of Al₂O₃–water nanofluid (1% vol.) and dual twisted tape inserts (DTI) with pitch ratios of 2, 3, and 4 on the performance of CPC. Important parameters such as absorbed heat flux, Nusselt number, and collector efficiency were quantified for various flow rates. Results indicate that at a pitch ratio of 2, the Nusselt number was boosted by a maximum of 365% and absorbed heat flux by 13.3% over water in a bare tube. Collector efficiency was enhanced by a maximum of 35.6%, with marginal increases in friction factor and pumping power. The enviro-economic analysis also exhibited CO₂ emission reductions of up to 12.3% and a 15% reduced payback period compared to the reference system. These observations affirm that the integration of nanofluids with turbulence-generating inserts provides a viable route to boost CPC performance, with possible applications in industrial process heating, desalination, and other green thermal systems.