Entropy balance in the presence of drift and diffusion currents: An elementary chaotic map approach

We study the rate of irreversible entropy production and the entropy flux generated by low-dimensional dynamical systems modeling transport processes induced by the simultaneous presence of an external field and a density gradient. The key ingredient for understanding entropy balance is the coarse graining of the phase-space density. This mimics the fact that ever refining phase-space structures caused by chaotic dynamics can only be detected by finite resolution. Calculations are carried out for a generalized multibaker map. For the time-reversible dissipative (thermostated) version of the model, results of nonequilibrium thermodynamics are recovered in the large system limit. Independent of the choice of boundary conditions, we obtain the rate of irreversible entropy production per particle as $u^2/D,$ where $u$ is the streaming velocity (current per density) and $D$ is the diffusion coefficient.