▎ 摘　　要

There are few studies on the behavior of nanofluids at temperatures below freezing, and their properties in cooling applications have not been studied in detail. Therefore, this study was conducted to investigate the effects of temperature and concentration of nanoparticles on the thermophysical properties of graphene-Al2O3/ethylene glycol-water hybrid nanofluid at low temperatures. The nanoparticles were characterized by BET, TEM, SEM and XRD methods. Hybrid nanofluids were prepared at room temperature by adding nanoparticles with different volume fractions (0.05-2.5%) to a base fluid containing a combination of water and ethylene glycol, and OA and SDS as surfactants. The density, thermal conductivity and surface tension of the hybrid nanofluids were determined experimentally in the temperature range of 253-303 K, and the results were compared with some existing theoretical models. The density measurements showed that the predictions of the mixture model agreed well with the experimental results. The thermal conductivity of the hybrid nanofluids depended on the temperature and concentration of the nanoparticles, especially at sub-zero temperatures. Based on the experimental results, a reliable correlation was presented to evaluate the thermal conductivity of the graphene-Al2O3/ethylene glycol-water hybrid nanofluid at different temperatures and nanoparticle concentrations. The dependence of surface tension on nanoparticle concentration has a critical limit. The surface tension of the hybrid nanofluid decreased with the presence of surfactant in the base fluid and with temperature. The obtained results are promising with respect to the use of the studied nanofluid in cooling applications.