Mpemba effect and phase transitions in the adiabatic cooling of water before freezing

In this paper, an accurate experimental investigation of the Mpemba effect (that is, of the fact that initially hot water freezes before the colder one) is carried out, showing that, in the adiabatic cooling of water, relevant roles are played by supercooling, and by phase transitions which take place at 6±1 C,3.5±0.5 C and 1.3±0.6 C. The last transition, which occurs with the non-negligible probability of 0.21 with respect to the total number of runs performed, has not been detected earlier. On the basis of our experimental results, we can present a thorough theoretical analysis of supercooling and of such phase transitions, which are interpreted in terms of the different ordering of molecule clusters in water.