# Helmholtz Thermodynamics Beyond Hamiltonians: Including Walls, Pressure and Heat Flow

## TL;DR

This paper extends Helmholtz thermodynamics to include walls, pressure, and heat flow, enabling the description of real thermodynamic processes like cycles and work extraction from purely mechanical Hamiltonian systems.

## Contribution

It introduces a framework incorporating heat flux and pressure into Helmholtz formalism, bridging the gap between mechanical systems and classical thermodynamics.

## Key findings

- Helmholtz formalism now accounts for pressure and heat flow.
- The approach models thermodynamic cycles such as Carnot.
- Extensions are validated on harmonic oscillator and elastic bouncer.

## Abstract

For 1D Hamiltonian systems with periodic solutions, Helmholtz formalism provides a tantalizing interpretation of classical thermodynamics, based on time integrals of purely mechanical quantities and without need of statistical description. Here we extend this approach to include heat flux and pressure at the walls, thereby enabling it to describe actual thermodynamic transformations, such as isothermal compressions and expansions. The presence of hard walls, which gives rise to non zero pressure, is justified by means of the virial theorem, while the heat fluxes are introduced as quasi-static limits of suitably thermostatted Hamiltonians. Particular attention is paid to generalizing the minimalist cases of the harmonic oscillator and elastic bouncer, which afford clear physical interpretations. With such extensions, a complete picture of thermodynamics emerges, amenable to cyclic transformations capable of producing mechanical work from heat, like the Carnot cycle.