When the Hotter Cools More Quickly: Mpemba Effect in Granular Fluids

TL;DR

This paper demonstrates the Mpemba effect in granular fluids, showing that hotter systems can cool faster than cooler ones, with analytical predictions confirmed by simulations.

Contribution

It extends the understanding of the Mpemba effect to granular fluids, providing analytical predictions and simulation validation for the conditions under which it occurs.

Findings

The Mpemba effect occurs in granular fluids under certain initial conditions.

Analytical models accurately predict the effect's occurrence.

Simulations confirm the theoretical predictions.

Abstract

Under certain conditions, two samples of fluid at different initial temperatures present a counterintuitive behavior known as the Mpemba effect: it is the hotter system that cools sooner. Here, we show that the Mpemba effect is present in granular fluids, both in uniformly heated and in freely cooling systems. In both cases, the system remains homogeneous, and no phase transition is present. Analytical quantitative predictions are given for how differently the system must be initially prepared to observe the Mpemba effect, the theoretical predictions being confirmed by both molecular dynamics and Monte Carlo simulations. Possible implications of our analysis for other systems are also discussed.