Finite time thermodynamics: limiting performance of diffusion engines and membrane systems

In this paper, the limiting performance of membrane systems with inhomogeneous composition is studied within the class of fixed rate processes. The problem of maintaining a nonequilibrium state in such a system using minimal power (separation problem) and the problem of extracting maximal power from such a system (diffusion engine problem) are formulated and solved. Results are obtained for diffusion engines with constant and periodic contact between the working body and the reservoirs.