Thermodynamic aspects of power production in thermal, chemical and electrochemical systems

We apply optimization methods to study power generation limits for various energy converters, such as thermal, solar, chemical, and electrochemical engines. Methodological similarity is observed when analysing power limits in thermal machines and fuel cells which are electrochemical flow engines. Operative driving forces and voltage are suitable indicators of imperfect phenomena in energy converters. The results obtained generalize our previous findings for power yield limits in purely thermal systems with finite rates. While temperatures Ti of participating media were only necessary variables in purely thermal systems, in the present work both temperatures and chemical potentials μk are essential. This case is associated with engines propelled by fluxes of both energy and substance. In dynamical systems downgrading or upgrading of resources may occur. Energy flux (power) is created in the generator located between the resource fluid (‘upper’ fluid 1) and the environmental fluid (‘lower’ fluid, 2). Fluid properties, transfer mechanisms and conductance values of dissipative layers or conductors influence the rate of power production. Numerical approaches to the dynamical solutions are based on the dynamic programming or maximum principle. Here we focus especially on the latter method, which involves discrete algorithms of Pontryagin’s type. Downgrading or upgrading of resources may also occur in electrochemical systems of fuel cell type. Yet, in this paper we restrict ourselves to the steady-state fuel cells. We present a simple analysis showing that, in linear systems, only at most ¼ of power dissipated in the natural transfer process can be transformed into the noble form of mechanical power.