Nanofluids are colloidal suspensions made of nanometer-sized particles dispersed in a conventional fluid. Their unusual thermal properties explain intensive investigations for several thermal and industrial applications. In this work, an experimental investigation was performed to measure the freezing point and to study the supercooling point made of alumina γ-Al2O3 nanoparticles with 30？nm diameter size and deionized water. Particles' volume fraction used in this work is ranging from 1% to 4%. The T-historic method based on the measurement of the point of inflexion was performed to measure the thermal properties such as the freezing point and the latent heat of solidification of the nanofluids for different concentrations. The results show that the supercooling degree decreases for the high particles volume concentrations and that the agglomeration does not influence the temperature of the freezing point. However, it makes the freezing process longer. 1. Introduction Nanofluids are liquids suspensions containing nanoparticles or nanofibers dispersed in a conventional liquid. Recent researches showed an interesting thermal capacity compared to the conventional liquids [1, 2]. Research efforts have mostly been concerned with the characterization of thermal and physical properties of nanofluids. Many experimental studies focused on the measurement of thermal conductivity [3, 4] and the measurement of dynamic viscosity [5, 6] usually for a range of temperature between 20°C and 60°C. Nguyen et al. [7] showed a singular phenomenon of hysteresis for high temperatures and high concentrations. Aladag et al. [8] studied the rheological behavior of alumina/water and aqueous nanotube of carbon nanofluids at low temperature (less than 10°C). Their results show the nanofluids are not Newtonian and that the experimental results of dynamic viscosity are much higher than those from the theoretical models. Several experimental investigations have revealed an enhancement of the thermal performance in exchangers [9, 10] and an impressive enhancement of the convective heat transfer coefficient in horizontal tubes [11], whereas many factors such as clustering of particles, agglomeration, sedimentation, and the dissociation of the surfactant on the effective thermal properties of nanofluids have an important effect on the results. The behavior of this type of fluid in a range of temperature below 20°C is not much studied. Some papers show that the behavior of these fluids at low temperature is no longer Newtonian. Khaled and Vafai [12] investigated the effect of the
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