Faster Heat Transfer Clarifies the Unexpected Twist in the Simultaneous Freezing of Hot versus Cold Water

Abstract: Water exhibits many unique properties compared to other liquids, with some of these explained and others remaining enigmatic. Among them, it was proposed and extensively debated that hot water would freeze faster than cold. Numerous studies have demonstrated the difficulty of successfully elucidating this effect, making explanations surrounding this phenomenon highly controversial. Here, we demonstrate that when two cups filled with cold and hot water are introduced simultaneously in a freezer saturated with ice-nucleating agents, the hot sample freezes faster and to a greater depth than the cold sample, particularly when the initial temperature difference is high. On the other hand, against some previous beliefs, the time to onset of crystallization is always and logically retarded for hotter samples. In these conditions, where supercooling is eliminated, and temperature recording is perfectly controlled, robust experiments follow the same trend, whether hot versus room temperature samples or RT versus cold samples are tested. Differences in heat transfer are proposed and simulated to explain such divergence in freezing time in compliance with Newton law. These results resolve the mystery surrounding the experimental Mpemba effect without questioning the burgeoning research on related effects.