Cycle Analyses for Thermoelectric Power Generation and Heat Pumps Using β″ Alumina Solid Electrolytes

Alkali metal thermoelectric conversion (AMTEC) cycles and the cycles of high-temperature heat pumps using beta “alumina solid electrolytes are analyzed, and it is shown that the isothermal expansion or compression of the Na+ flow through the electrolyte coincides with the expansion or compression process, respectively, in the Ericsson cycle when the internal losses by the electrolyte and the thin electrode are small. It is also shown that the isothermal compression approximation in the heat pump cycle is more consistent with the AMTEC cycle than the adiabatic compression discussed in an earlier report. Typical results for voltage-current characteristics and thermal efficiencies of the AMTEC and the heat pump, including the high-temperature side Na conditions of not only the saturated liquid, but also the super-heated vapor, are presented. The super-heat operation shows a decrease in the power generation efficiency for the AMTEC and an increase in the coefficient of performance for the heat pump.