On thermoelectric power conversion from heat recirculating combustion systems

The thermodynamic theory governing the absolute maximum efficiency of energy conversion by thermoelectric devices that operate as part of the heat recycle in regenerative burners is examined. Comparison with a series of elementary Carnot cycles helps to address the question of whether higher system efficiencies are realizable by rejecting the unconverted heat to the cold surroundings or to the incoming reactants as part of the recycle. While for the second law (Carnot) heat engine cycles the maximum power that can be extracted is independent of the layout, in the case of irreversible thermoelectric assemblies a particular combination of both in a novel configuration is shown to be most advantageous. This heat exchanger/thermoelectric converter configuration consists of a coaxial assembly of many annular thermoelectric elements in series and a section in which heat is rejected to the incoming reactants that is followed by a second section, which discards unconverted heat to the cold surroundings. It is shown that the efficiencies of such devices could substantially exceed the maximum efficiencies of the best present-day thermoelectric conversion systems, and the theory suggests practical designs for small, combustion-driven, power supplies.