We study a process of heat transfer between a body of heat capacity C(T) and a sequence of N heat reservoirs, with temperatures equally spaced between an initial temperature T0 and a final temperature T N. The body and the heat reservoirs are isolated from the rest of the universe, and the body is brought in thermal contact successively with reservoirs of increasing temperature. We determine the change of entropy of the composite thermodynamic system in the total process in which the temperature of the body changes from T0 to T N. We find that for large values of N the total change of entropy of the composite process is proportional to (T N - T0) / N, but eventually a non-monotonic behavior is found at small values of N.
second law of thermodynamics; entropy; reversible and irreversible processes; heat exchange
