Mesoscopic Heat engines beyond the Limits of Thermodynamics

Abstract

Despite the central role that Equilibrium thermodynamics has played in our understanding of many body systems, the underlying theoretical construct is strictly correct only in the ‘Thermodynamic Limit’. On the other hand, biological micromotors that function in a regime where this limit is violated are known to perform with a superior efficiency even in the absence of temperature differences. In this thesis, we discuss the design and operation of heat engines that successively defy the three conditions involved in this limit viz. quasi-static limit, macroscopic limit and equilibrium limit and explore the consequences of this on their performance. While all macroscopic engines that surpass the quasi-static limit are known to compromise efficiency for power, we demonstrate that by further breaching the macroscopic limit and using a Gaussian colored noise, such a trade-off might not even be necessary. Our results indicate that for engines with low degrees of freedom, in the presence of a colored Gaussian noise, even the quasi-static efficiency can be exceeded at finite times. We examined the operation of heat engines beyond the equilibrium and macroscopic limits by introducing motile bacteria into the surrounding bath. Under the influence of the active noise due to the bacterial motion, we observed that the performance increased by orders of magnitude surpassing even the equilibrium quasi-static efficiency at infinite temperature difference. Finally, we demonstrated that generating macroscopic motion by grouping engines that trespass the limits of thermodynamics, can further result in even better performance and tunability. Our results highlight that the major constraints imposed by equilibrium and finite time thermodynamics can be relaxed by employing a bottom-up architecture and calls for rethinking the fundamentals of the approaches to engine design