Tailoring the First Law of Thermodynamics for Convective Flows

Abstract

The basis of equilibrium thermodynamics is the law of energy conservation. Thermodynamics applies this fundamental law in a specific manner by focusing on how a system exchanges energy with its environment during transitions between equilibrium states, characterized by quantities such as heat absorbed by the system and the work required to change its volume. Motivated by the possible existence of an equally simple thermodynamic-like description beyond equilibrium, we investigate global energy exchange in transitions between out-of-equilibrium states. We study a system with heat flow and an external (gravity) field that exhibits macroscopic motion, such as Rayleigh-Bènard convection. The results show that the system’s energy exchange has the same form as in equilibrium. It opens the possibility of describing out-of-equilibrium systems using a few simple laws similar to equilibrium thermodynamics.