Investigation of the effects of binary hybrid nanofluids and different arrangements of corrugated tubes on thermal performance

This research examined the effects of corrugation distance and nanofluid volume concentration on pressure drop, Nusselt number, and thermal performance in a circular tube. Binary nanofluid (MWCNT/Al₂O₃, 60:40) with volume fractions of 0.25%, 0.5%, and 1% was tested in corrugated tubes with distances of 10 mm, 20 mm, and 30 mm under constant heat flux (20 kW/m²) for Reynolds numbers between 10,000 and 40,000. 3D single-phase model using ANSYS 19 with the standard k-ε turbulence model was employed and validated against literature equations. Results revealed that heat transfer improved with increasing Reynolds number, primarily due to elevated flow rates and intensified mixing induced by the corrugated surfaces. Compared to smooth tubes, the corrugated tubes exhibited higher Nusselt numbers, signifying better convective heat transfer performance. Nonetheless, this improvement was accompanied by increased friction factors and pressure drops, especially at shorter corrugation distances. Shorter corrugation distances intensified turbulence and mixing, enhancing heat transfer, while longer distances diminished turbulence, lowering the Nusselt number. The optimal thermal performance, with a performance evaluation criterion of 1.27, was achieved at a corrugate distance of 10 mm and MWCNT/Al₂O₃ nanofluid concentration of 1%. This research highlights the influence of corrugate distance on the thermal efficiency of corrugated tubes.