Erosion-Corrosion Wear of Heat-Exchanger Materials by Water/Ethylene-Glycol/Alumina Nanofluids

Erosion-Corrosion Wear of Heat-Exchanger Materials by Water/Ethylene-Glycol/Alumina Nanofluids

Gustavo J. Molina (Georgia Southern University, Statesboro, USA), Fnu Aktaruzzaman (Georgia Southern University, Statesboro, USA), Valentin Soloiu (Georgia Southern University, Statesboro, USA) and Mosfequr Rahman (Georgia Southern University, Statesboro, USA)
DOI: 10.4018/IJSEIMS.2018070101
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Nanofluids are suspensions of nanoparticles in ordinary coolants, but their tribological effects on heat-exchanger materials are unknown. Previous research has explored wear from distilled-water-base nanofluids only, while most engine-coolants are alcohol solutions in water. This article presents testing of aluminum and copper by jet impingement of 50%-ethylene-glycol in water solution and of its 2%-alumina nanofluid. The effects are investigated of nanoparticle addition on the anticorrosion protection provided by ethylene glycol. The observed modifications showed that ethylene-glycol in water nanofluid led to wear patterns that were different than those obtained with the base-fluid; nanoalumina addition enhanced erosion and corrosion on aluminum and copper. Comparing the effects of ethylene glycol and its nanofluid solutions to those from same tests performed with distilled-water and its nanofluid suggests that nanopowders can substantially enhance wear by decreasing the anticorrosion action of ethylene glycol by a synergetic mechanism of erosion-corrosion
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Early research on nanofluid tribology was conducted by Roubort et al (2008) and by Singh (2009) at the US Dept. of Energy. Their works suggested that no significant surface changes would occur to aluminum 3003 samples when jet-impacted for 750 hours by the tested nanofluid. They employed the nanofluids of SiC-in-water, and of Cu- and Al-oxides in ethylene- and trichloroethylene-glycol with 2%-added nanopowders. Test velocities were of 8 to 9 m/s and impact angle of 30°; the extrapolation of that limited material-removal data would predict an erosion rate as low as 0.065 milligrams/year if such nanofluids were employed in vehicle-radiators.

Nguyen et al (2008) later found, however, that a significant total mass-loss can be obtained from aluminum specimens subjected for 180 hours to a 9.6m/s jet-impingement of a 5% alumina-in-water nanofluid. Celata et al (2011, 2014) tested the jet-impingement effects on aluminum, copper, and stainless steel by the nanofluids of TiO2, Al2O3, and ZrO2 (each at 9% concentration) in distilled water. They compared the measured material-removal rates (by profilometer scanning) to those obtained when the same materials were impacted by water-only jets. Significant material-removal differences were measured on aluminum targets for the TiO2, Al2O3, and ZrO2 nanofluids, while for copper such surface modifications occurred only when treated with the ZrO2 nanofluid. They observed no differences in material removal for stainless steel. Those test strongly suggested that nanofluids impact on aluminum and copper surfaces could lead to higher erosion rates than those obtained by distilled water only. George et al (2014) presented the erosion effects on aluminum and cast iron of a 0.1%-TiO2 in distilled water nanofluid. They conducted tests for up to 10 hours of jet-impingement at 5m/s and 10m/s and for varied impingement angles. They found that the rates of erosion (measured by specimen weighing) reached maxima at a 20◦ angle of impingement for aluminum, and at 90◦ for cast iron.

Most of the reported tests in existing literature were carried out, however, for fluid speeds much higher than those of actual cooling systems. In some cases, as in Roubort et al (2008) and Singh (2009), the employed nanopowder concentrations were substantially higher than those of practical nanofluids. Nanopowder-concentrations higher than 2% lead to large increases of viscosity which could likely offset the sought heat transfer enhancement, because of an actual reduction of the system overall cooling efficiency. Molina et al (2014) showed that a 5% concentration of alumina-nanopowder when added to distilled water increased by three times the dynamic viscosity, and by as much as 5.5 times when mixed in solutions of ethylene-glycol in water. The review work of Younes (2015) on nanofluid thermal conductivity discussed those large increases of nanofluid viscosity for high nanopowder concentrations.

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