Effect on performance of a CTHE by using twisted tapes and Al₂O₃ nanofluids: an experimental study and correlation development

The current energy crisis is causing a transformation of tremendous scope and complexity. The natural gas, coal, and electricity sectors have experienced the largest tremors. In this regard, an effort was made to conserve energy by providing a compact heat exchanger that may be utilized to recover waste heat from power plants and industries. This article explores the effect of combined passive techniques on the performance of a CTHE fitted by twisted tapes at hot-side and Al₂O₃ nanofluid used as cold-side fluid. The experiments were conducted by incorporating the differently configured PVTTs and CFTTs (TR: 20, 13.3, and 9.8) in the inner tube with fixed flowrate (Re = 2500) of hot water and using different volume fractions of Al₂O₃ nanofluid (Vol.%: 0.05, 0.1 and 0.15) as cold fluid with varied flow rates (500 ≤ Re ≤ 5000) in the annulus. The results reveal that the PVTT (TR = 20) and 0.05% nanofluid combination increases the Nusselt number by 12.28% and the TPF by 1.127, while the CFTT (TR = 9.8) and 0.15% nanofluid combination increases the Nusselt number by 24.27% and the TPF by 1.263. Hence, CFTT (TR = 9.8) with 0.15% of Al₂O₃ nanofluid provided greater performance in the combinations tested, albeit at the expense of a little pressure loss.