Abstract
We study a refrigerator model which consists of two -level systems interacting via a pulsed external field. Each system couples to its own thermal bath at temperatures and , respectively . The refrigerator functions in two steps: thermally isolated interaction between the systems driven by the external field and isothermal relaxation back to equilibrium. There is a complementarity between the power of heat transfer from the cold bath and the efficiency: the latter nullifies when the former is maximized and vice versa. A reasonable compromise is achieved by optimizing the product of the heat-power and efficiency over the Hamiltonian of the two systems. The efficiency is then found to be bounded from below by (an analog of the Curzon-Ahlborn efficiency), besides being bound from above by the Carnot efficiency . The lower bound is reached in the equilibrium limit . The Carnot bound is reached (for a finite power and a finite amount of heat transferred per cycle) for . If the above maximization is constrained by assuming homogeneous energy spectra for both systems, the efficiency is bounded from above by and converges to it for .
- Received 18 December 2009
DOI:https://doi.org/10.1103/PhysRevE.81.051129
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