Abstract
The construction of efficient thermal engines operating at finite times constitutes a fundamental and timely topic in nonequilibrium thermodynamics. We introduce a strategy for optimizing the performance of Brownian engines, based on a collisional approach for unequal interaction times between the system and thermal reservoirs. General (and exact) expressions for thermodynamic properties and their optimized values are obtained, irrespective of the driving forces, asymmetry, temperatures of reservoirs, and protocol to be maximized. Distinct routes for the engine optimization, including maximizations of output power and efficiency with respect to the asymmetry, the force, and both of these, are investigated. For the isothermal work-to-work converter and/or a small difference in temperature between reservoirs, they are solely expressed in terms of Onsager coefficients. Although the symmetric engine can operate very inefficiently depending on the control parameters, the usage of distinct contact times between the system and each reservoir not only can enhance the machine performance (signed by an optimal tuning ensuring the largest gain) but also enlarges substantially the machine regime operation. The present approach can pave the way for the construction of efficient Brownian engines operating at finite times.
Highlights
A long-standing dilemma in thermodynamics and related areas concerns the issue of mitigating the impact of thermal noise or wasted heat in order to improve the machine performance
We introduce a strategy for optimizing the performance of Brownian engines, based on a collisional approach for unequal interaction times between the system and thermal reservoirs
A second fundamental point concerns the fact that, even if all sources of dissipation could be mitigated, the performance of any thermal machine would still be limited by Carnot efficiency, which requires the occurrence of infinitely slow quasistatic processes, and the engine operates at null power
Summary
A long-standing dilemma in thermodynamics and related areas concerns the issue of mitigating the impact of thermal noise or wasted heat in order to improve the machine performance. Isothermal transformations are slow, demanding a sufficiently large number of stages for achieving the desired final state For this reason, distinct protocols, such as increasing the coupling between the system and the thermal bath, have been undertaken for speeding it up and simultaneously controlling the increase in dissipation [28,29,30,31,32]. Our approach is based on a Brownian particle sequentially placed in contact with distinct thermal baths and subject to external forces [33] for unequal times Such a description, referred to as collisional, has been successfully employed in different contexts, such as systems that interact only with a small fraction of the environment and those presenting distinct drivings over each member of the system [34,35,36,37]. IV, and explicit calculations of the Onsager coefficients and linear regimes are presented in Appendixes A–C
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