A 2-dimensional thermal-hydraulic model for conical and flat evaporators and the liquid soidijm return artery in multi-tube Alkali-Metal Thermal-to-Electric Converter (AMTEC) cells is developed, to predict incipient dryout in the evaporator wock. The governing equations and numerical procedue used are described in details. Model results of the electrical power ouput matched experimental data, but the evaporator temperature was consistently 50 K higher than measurements. This difference in evaporator temperature may be attributed to a sodim vapor leakage through the BASE brazes or condensation inside the BASE tubes. Incipient dryout is predicted in the evaporator wick surface at the standoff wall, when either the hot side temperature exceeds, or the ceel electrical current (or sodium flow rate) drops below a cut-off value. Flat and shallow (45 deg ) conical evaporators exhibit the highest capillary limit and are thus recommended for use in PX-type AMTEC cells.
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