Thermodynamics of enhanced heat transfer: a model study

TL;DR

This paper models enhanced heat transfer between two thermal baths, demonstrating that efficiency of external control is bounded similarly to Carnot efficiency, revealing fundamental thermodynamic limits.

Contribution

The study introduces a thermodynamic model for externally controlled heat transfer, establishing a bound on efficiency analogous to Carnot's limit, and clarifies the thermodynamics of process enhancement.

Findings

Efficiency bound is T_c/(T_h - T_c)

Enhanced heat transfer requires work consumption

Efficiency shares features with Carnot limit

Abstract

Situations where a spontaneous process of energy or matter transfer is enhanced by an external device are widespread in nature (human sweating system, enzyme catalysis, facilitated diffusion across bio-membranes, industrial heat exchangers). The thermodynamics of such processes remains however open. Here we study enhanced heat transfer by a model junction immersed between two thermal baths at different temperatures $T_h$ and $T_c$ ($T_h>T_c$). The transferred heat power is enhanced via controlling the junction by means of external time-dependent fields. Provided that the spontaneous heat flow process is optimized over the junction Hamiltonian, any enhancement of this spontaneous process does demand consumption and subsequent dissipation of work. The efficiency of enhancement is defined via the increment in the heat power divided over the amount of consumed work. We show that this efficiency is bounded from above by $T_c/(T_h-T_c)$. Formally this is identical to the Carnot bound for the efficiency of ordinary refrigerators which transfer heat from cold to hot. It also shares some (but not all) physical features of the Carnot bound.