Thermal designing on a small-sized AMTEC cell

The present paper discusses thermal designing and performance of a compact type AMTEC system. The compact type AMTEC system uses multiple small-sized cell components, which consist of sodium beta"-alumina solid electrolyte tubes of 3 mm in outer diameter and simple freestanding type capillary structure. When the cell components are arranged in a canister, the pressure drop due to sodium vapor flow from the electrode to the condenser becomes a critical parameter. The effect of the pressure drop was analytically evaluated and the optimum geometrical arrangement was considered. The typical calculated result shows that a 37-tube cell having a base area of 7.5 cm² has a predicted output power of about 5 W at relatively low operating temperature of 900 K. This output power is almost equal to that of the high temperature type cells operating around 1,100 K. Structure and heat transfer analyses necessary for the miniaturization and the low temperature operation are reported in this paper. Preliminary thermal design on a cascaded system with the AMTEC and the thermionic converter is also discussed.