Cycle analyses of thermoelectric power generation and heat pumps using the β″-alumina electrolyte

Cycle analyses of the alkali-metal thermoelectric conversion (AMTEC) and the high-temperature heat pump using the β″-alumina electrolyte was performed. It is shown that the isothermal expansion or compression of the sodium ion flow through the electrolyte coincides with the expansion or compression process in the Ericsson cycle, respectively, when the internal losses by thin electrolyte and electrodes are small. The isothermal compression approximation in the heat-pump cycle is more consistent with the isothermal expansion in the AMTEC cycle than the adiabatic compression discussed in an earlier report. Typical voltage-current characteristics and thermal efficiencies for both the AMTEC and the heat pump are presented including not only the saturated liquid case, but also the superheated vapour case of sodium at the high temperature side. The operation in superheated vapour shows a decrease in the power-generation efficiency for the AMTEC and an increase in the coefficient of performance for the heat pump.