Pankaj Mehta, Anatoli Polkovnikov
Increasing the efficiency of engines is a long-standing technological problem. The second law of thermodynamics ensures that the efficiency of any engine must be below the Carnot bound. The idealized engines traditionally considered in thermodynamics operate using two reservoirs, a hot reservoir that provides energy and a cold reservoir that serves as an entropy sink. Here we consider a different but more common class of nonequilibrium engines with a single reservoir. By extending fundamental thermodynamic relations to nonequilibrium processes, we find a rigorous thermodynamic bound for the efficiency of single-reservoir engines which is below the Carnot efficiency. We show that the efficiency of these engines can be increased by using non-ergodic engines to perform work and illustrate these ideas using simple examples. These results suggest a new general strategy for designing more efficient engines.
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http://arxiv.org/abs/1207.5818
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