Figure 2.
Illustration of the evolution towards (a) a state of thermodynamic equilibrium (TE) for an isolated system, and (b) a state that is maintained away from TE for a non-isolated system that exchanges entropy with the surroundings. The symbols represent: S, the entropy of the system; Fab, the heat flux from box a to b; Ta and Tb, the temperatures of the respective boxes; Fin, the heat flux into the system; Fout, the heat export from the system to the surroundings. NEE, net entropy exchange. (Adapted from Kleidon (2009b).)