Power Generation Limits in Thermal, Chemical and Electrochemical Systems

Abstract

Power generation limits are evaluated via optimization for

various energy converters, such like thermal, solar, chemical, and

electrochemical engines, in particular fuel cells. Thermodynamic

analyses lead to converters’ efficiencies, which help to solve problems

of optimal upgrading and downgrading of resources. While methods of

static optimization, i.e. differential calculus and Lagrange multipliers,

are sufficient for steady processes, dynamic optimization applies the

variational calculus and dynamic programming for unsteady processes.

In reacting systems chemical affinities constitute prevailing

components of an overall efficiency, thus flux balances are applied to

derive power in terms of active parts of chemical affinities.

Methodological similarity is observed when treating power limits in

flow thermal machines and fuel cells. The examples show power

maxima in fuel cells and prove suitability of a thermal machine theory

to chemical and electrochemical systems. The main novelty of

contribution in the fuel cell context consists in introducing an effective

change of Gibbs free energy between products p and reactants s which

takes into account lowering of voltage and power caused by the

incomplete conversion of the overall electrochemical reaction.