The effect of TiO2 nanoparticles on fluid quenching characteristics

Abstract

Nanofluids are colloidal suspensions of nanoparticles in base fluids. Some of the particles used in recent research are metal oxide and carbide particles, such as SiC, CuO, Al₂O₃ and TiO₂, graphite and carbon nanotubes and particles. Quenching in such colloids results in better cooling abilities, higher impact toughness and smaller dimension changes of steels, compared with pure quenching media. In this investigation, nanofluids with TiO₂ powders of 50 nm average particle size were investigated. Base fluids of primary interest were deionised (DI) water, some commercial quenching oils and polyalkylene glycol water solution of various polymer concentrations, 5–30 vol.-%. The investigated fluids were prepared with the addition of the same TiO₂ powder with different concentrations, from extremely low, 10 mg nanopowder per litre to 1 g L^?1. The cooling characteristics of these colloids were compared with the results of base fluids, but also with the results of previous measurements carried out on the fluids with addition of Al₂O₃ micrometre and submicrometre size particles. All of the cooling curves were measured and recorded by the IVF Smart Quench system using a stainless steel probe of 12·5 mm diameter in accordance with ISO 9950 standard. The cooling rate (CR) versus temperature and time was compared for all of the investigated media. The preparation of fluids was conducted with great care, with respect to mechanical stirring and sonification times. The average particle size was measured for each case. In order to better understand the phenomena that occur during the quenching process, a high speed camera was used for recording the experiments. Titanium oxide nanoparticles show the most significant effects on the cooling properties of the water based polymer solution. The maximum cooling rate increases with higher particle concentration. When comparing the results of experiments with alumina particles, smaller and thermally less conductive TiO₂ particles show greater effects on nanofluid properties.