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Thermodynamic Variational Principle Unifying Gravity and Heat Flow
Naoko Nakagawa1, Shin-Ichi Sasa2
1Ibaraki University, Department of Physics, Mito 310-8512, Japan.
Physical Review Letters
|February 22, 2026
Summary
Predicting liquid-gas configurations under conflicting gravity and heat flow is challenging. A new global thermodynamics framework unifies these effects into "effective gravity" (g_eff), determining stable phase arrangements.
Area of Science:
- Thermodynamics
- Fluid Dynamics
- Phase Transitions
Background:
- Standard equilibrium thermodynamics fails for nonequilibrium steady states.
- Predicting liquid-gas configurations is difficult when gravity and heat flow conflict.
Purpose of the Study:
- To develop a framework for predicting stable phase configurations in liquid-gas systems under competing drives.
- To address state selection problems in nonequilibrium steady states.
Main Methods:
- Proposed a variational principle based on extended thermodynamics, termed global thermodynamics.
- Unified gravity and heat flow effects into a single parameter, effective gravity (g_eff).
Main Results:
- The sign of effective gravity (g_eff) dictates the stable configuration.
- g_eff > 0 indicates liquid at the bottom; g_eff < 0 indicates liquid above gas.
Conclusions:
- Global thermodynamics offers a quantitative tool for predicting phase configurations under competing influences.
- The effective gravity parameter provides a novel approach to understanding nonequilibrium system behavior.
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