A Single-granule Stirling Heat Engine

TL;DR

This paper demonstrates a macroscale Stirling engine using a vibrofluidized granule with controllable temperature and confinement, reproducing universal thermodynamic principles and revealing novel dissipation mechanisms.

Contribution

It introduces a macroscopic, athermal Stirling engine with independent control over temperature and confinement, bridging microscopic thermodynamics and macroscale engineering.

Findings

Achieves Curzon-Ahlborn efficiency at maximum power.

Reproduces universal power-efficiency trade-offs of finite-time thermodynamics.

Discovers a control-dependent damping leading to unexpected dissipation.

Abstract

Single-particle heat engines at atomic and colloidal scales obey the universal thermodynamic bounds on work and efficiency. Here, we translate these principles to the macroscale by building an athermal Stirling engine whose working medium is a millimeter-sized, vibrofluidized granule confined in a time-dependent magnetic trap. By embedding a rattler within the granule to inject noise, we engineer overdamped, Brownian-like dynamics in an otherwise inertial particle. This design enables independent control over the granule's effective temperature and spatial confinement. Our engine quantitatively reproduces the universal power-efficiency trade-offs of finite-time thermodynamics, achieving the Curzon-Ahlborn efficiency at maximum power. Strikingly, we uncover a control parameter-dependent damping that leads to an unexpected dissipation mechanism - the losses in the compression stroke rival or even exceed those during expansion. Our work establishes an accessible experimental platform to study small-system thermodynamics in intrinsically athermal systems.