Author(s): Henrique Palhares

Abstract: Can a simple passive insert raise the thermal performance of a viscous binary mixture by a measurable margin without excessive pumping penalty? This research addressed that question by examining forced convective heat transfer inside a copper circular tube fitted with aluminium twisted-tape inserts at three twist ratios (y = 3, 5 and 7). Glycerol–water mixtures at volumetric concentrations of 20%, 40% and 60% served as the working fluid under uniform wall heat flux conditions. Reynolds numbers ranged from 800 to 2300, covering the laminar-to-transitional regime. Wall and bulk temperatures were recorded by calibrated T-type thermocouples at eight axial stations, and volumetric flow was metered with a Coriolis-type sensor. Mean Nusselt numbers, Darcy friction factors and performance evaluation criteria (PEC) were derived from the measured data. At 20% glycerol and y = 3, the mean Nusselt number reached 52.6, representing an 85.2% gain over the plain-tube baseline (Nu = 28.4). Higher glycerol fractions dampened the enhancement; the 60% mixture at y = 3 yielded a 97.3% rise relative to its own plain-tube value, yet the absolute Nusselt number was lower owing to the elevated Prandtl number. Friction factors grew by 18–37% depending on twist ratio and concentration, but the PEC remained above unity for every combination tested, peaking at 1.34 for y = 3 and 20% glycerol. The results confirm that twisted-tape inserts deliver a net thermohydraulic benefit when processing glycerol–water mixtures at moderate Reynolds numbers, and the data set provides empirical correlations suitable for heat-exchanger pre-design.

DOI: https://www.doi.org/10.22271/27078043.2026.v7.i2a.137

Pages: 51-55 | Views: 93 | Downloads: 36

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