Nanofluids are suspensions of solid metals, oxides, carbides or nitrides nanoparticles, or of carbon nanotubes or nanofibers (typically up to 5%) in a continuous and saturated cooling fluid (as water, and ethylene glycol). They are predicted to have higher thermal conductivity and heat transfer coefficients than those of the base fluids, and they are promising as coolants for critical-cooling systems. However, many unknowns remain, particularly about nanofluid wear and erosion of cooling system materials: Initial research at US DOE suggested no erosion on aluminum 3003 impacted by a 2 %vol. SiC-nanofluid jet, for 750 hours at 8m/s. Singh found no significant erosion using Cu and Al oxides in ethylene and tricloro-ethylene glycols at of 9m/s. Nguyen reported small but significant wear effects on aluminum jet-impinged with 5% alumina-in-water nanofluid at 9.6 m/s for 180 hours. Recent work found significant increase of erosion (up to 300-times, as compared to base fluid) on aluminum for TiO2, Al2O3, and ZrO2 nanofluids ZrO2 (each at 9%) in distilled water, as they compared to water-only, and on copper only in the case of ZrO2 nanofluid. George recently presented erosion-jet effects of 0.1%-vol. TiO2 in water nanofluid, for up to 10 hs (at 5m/s and 10m/s) at different angles on aluminum and cast iron, by measuring weight loss and roughness by speckle interferometry. They found that erosion would reach maxima at a 20 degree-angle of impingement for aluminum, and at 90 degree for cast iron. SEM and AFM showed that corrosion assisted erosion caused removal in cast iron, and abrasive erosion and smoothening caused wear on aluminum.
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