Direct observation of the Mpemba effect with water: Probe the mysterious heat transfer

Abstract

The Mpemba effect is one of the most perplexing puzzles in nature. Although it has been discussed extensively, direct observation of the Mpemba effect is extremely challenging and rare. Herein, we report the first systematic study of the Mpemba effect with water and clearly point out the conditions required for the observation of the Mpemba effect. The results demonstrate that hot water usually has a faster cooling rate than cold water. The initial temperature, temperature difference, shape of the container, and water volume influence the heat exchange and the cooling process. Owing to the influential factors of heat exchange, the Mpemba effect can only be observed under specific conditions. This work helps to clarify doubts and confusion about the Mpemba effect and can offer alternative strategies for energy storage and transfer materials. (Figure presented.).