Universal bounds on cooling power and cooling efficiency for autonomous absorption refrigerators

TL;DR

This paper establishes universal bounds on the cooling power and efficiency of autonomous absorption refrigerators in the linear response regime, revealing a hierarchy of fluctuations and bounds that saturate in the tight-coupling limit.

Contribution

It introduces a hierarchy of fluctuation bounds for absorption refrigerators based on Onsager relations and thermodynamic uncertainty principles, applicable to different interaction regimes.

Findings

Hierarchy of fluctuation bounds for cold, hot, and work currents.

Tightest bound given by work current fluctuation.

Bounds saturate in the tight-coupling limit.

Abstract

For steady-state autonomous absorption refrigerators operating in the linear response regime, we show that there exists a hierarchy between the relative fluctuation of currents for cold, hot, and work terminals. Our proof requires the Onsager's reciprocity relation along with the refrigeration condition that sets the direction of the mean currents for each terminal. As a consequence, the universal bounds on the mean cooling power, obtained following the thermodynamic uncertainty relations, receive a hierarchy. Interestingly, within this hierarchy, the tightest bound is given in terms of the work current fluctuation. Furthermore, the relative uncertainty hierarchy hands over additional bounds that can be tighter than the bounds obtained from the thermodynamic uncertainty relations. Interestingly, all of these bounds saturate in the tight-coupling limit. We test the validity of our results for two paradigmatic absorption refrigerator models: (i) a four-level working fluid and (ii) a two-level working fluid, operating, respectively, in the weak (additive) and in the strong (multiplicative) system-bath interaction regime.