A comparative analysis of efficiency at maximum power output for heat engines

In this work, we present a comparative analysis of the efficiencies at maximum power output for different devices; first, we analyze the expressions of the efficiency at maximum power for two models of heat engines: a model of Curzon-Ahlborn (macroscopic) and a Novikov model, in these two cases, two kinds of heat transfer laws were considered; first, a heat transfer due to free convection described by Newton's Law of cooling and, second, a phenomenologic heat transfer comes from linear irreversible thermodynamics. On the other hand, we present the efficiencies at maximum power for stochastic (mesoscopic) heat engines obtained by Schmiedl and Seifert (2008), and for a Ratchet device, we also compared these efficiencies with the results presented recently by Esposito et al. (2010). For comparing, we expanding the expressions of efficiencies up to the third-order in term of η_c, where η_h is the efficiency of Carnot. We found some interesting similarities for the expressions of efficiencies between the macroscopic and mesoscopic models of heat engines.