In direct combustion-thermoelectric energy conversion, direct fuel injection and reciprocation of the air flowing in a solid matrix are combined with the solid-gas interfacial heat transfer and the solid conduction to allow for obtaining superadiabatic temperatures at the hot junctions. While the solid conductivity is necessary, the relatively large thermal conductivity of the available high-temperature thermoelectric materials (e.g., Si–Ge alloys) results in a large conduction loss from the hot junctions and deteriorates the performance. Here, a combustion-thermoelectric tube is introduced and analyzed. Radially averaged temperatures are used for the fluid and solid phases. A combination of external cooling of the cold junctions, and direct injection of the fuel, has been used to increase the energy conversion efficiency for low thermal conductivity, high-melting temperature thermoelectric materials. The parametric study (geometry, flow, stoichiometry, materials) shows that with the current high figure of merit, high temperature Si0.7Ge0.3 properties, a conversion efficiency of about 11 percent is achievable. With lower thermal conductivities for these high-temperature materials, efficiencies about 25 percent appear possible. This places this energy conversion in line with the other high efficiency, direct, electric power generation methods. [S0022-1481(00)01304-9]
Estimating Energy Conversion Efficiency of Thermoelectric Materials: Constant Property Versus Average Property Models
