Unraveling Specific Conditions for a Repeatable Mpemba Effect

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 water. 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. Besides, against some previous beliefs, the time to onset of crystallization is always and logically retarded for hotter samples. Under the conditions where supercooling is eliminated and temperature recording is precisely controlled, robust experiments follow the same trend, regardless of whether hotter or colder versus RT samples are tested. Differences in heat transfer are proposed and simulated to explain such divergence in freezing time in compliance with Newton's law. This work confirms the original study of Mpemba and Osborne, whose results have been so difficult to replicate, without questioning the burgeoning research on related effects.