Performance analysis of a multitube vapor-anode AMTEC cell

A detailed AMTEC performance and evaluation analysis model (APEAM) was developed to predict the performance of next-generation Pluto Express vapor-anode multitube cells. APEAM incorporates an axial electrochemical model, which accounts for the effects of nonuniform axial temperature and vapor pressure profiles along the BASE tubes; a detailed vapor pressure loss model, which includes free-molecular, transition and continuum flow regimes; and a comprehensive radiation/conduction model, which incorporates the effects of circumferential thermal shields above the BASE tubes and conduction studs between the hot end of the cell and the tubes support plate. Model results compared well with measured electrical power and experimental I-V characteristics of the PX-2C cell, recently tested at Phillips Laboratory. The cell peak electric power of 4.4 We occurred at an external load resistance of 3.0 Ω. At higher load resistance (or lower load demand), the PX-2C cell was load-following. Results also showed that the vapor flow on the low-pressure side of PX-2C was in the transition regime. The evaporator wick provided the sodium flow rate (8 g/hour) necessary to operate the cell at an evaporator temperature of about 950 K. The model predicted that using a molybdenum thermal shield on the inside of the cell wall, near the condenser, would increase the cell electric power and conversion efficiency by ~23%