A search for the Mpemba effect: When hot water freezes faster then cold water

TL;DR

This paper investigates the conditions under which hot water can freeze faster than cold water, emphasizing supercooling and spontaneous freezing temperature differences, and reports consistent observations of this phenomenon.

Contribution

It provides an experimental analysis of the Mpemba effect, highlighting the roles of supercooling and spontaneous freezing temperature differences in hot water freezing faster.

Findings

Hot water can freeze before cold water under specific conditions.

Supercooling and spontaneous freezing temperature differences are key factors.

The phenomenon was consistently observed in 28 out of 28 attempts.

Abstract

An explanation for why hot water will sometime freeze more rapidly than cold water is offered. Two specimens of water from the same source will often have different spontaneous freezing temperatures; that is, the temperature at which freezing begins. When both specimens supercool and the spontaneous freezing temperature of the hot water is higher than that of the cold water, then the hot water will usually freeze first, if all other conditions are equal and remain so during cooling. The probability that the hot water will freeze first if it has the higher spontaneous freezing temperature will be larger for a larger difference in spontaneous freezing temperature. Heating the water may lower, raise or not change the spontaneous freezing temperature. The keys to observing hot water freezing before cold water are supercooling the water and having a significant difference in the spontaneous freezing temperature of the two water specimens. We observed hot water freezing before cold water 28 times in 28 attempts under the conditions described here.