Performance analyses of an Nb±1Zr/C-103 vapor anode multi- tube alkali-metal thermal-to-electric conversion cell Mohamed S. El-Genk * , Jerey C. King Department of Chemical and Nuclear Engineering, Institute for Space and Nuclear Power Studies, University of New Mexico, Albuquerque, NM 87131, USA Received 20 December 1999; accepted 15 May 2000 Abstract The results of performance analyses of a refractory Nb±1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion (AMTEC) cell are presented and discussed. This cell could be used with a radioisotope heater unit to provide electric power from tens to a few hundreds of watts. In the tens of kilowatts electric range, the AMTEC cells could be used with a parabolic solar concentrator or a nuclear reactor heat source. The present cell measures 41.27 mm in diameter and is 125.3 mm high and has eight sodium beta 00 -alumina solid electrolyte (BASE) tubes, which are connected electrically in series to provide a load voltage in excess of 3 V. The hot structure of the cell, including the hot plate, the BASE tube support plate, the hot plenum wall and conduction stud, the evaporator stando and porous wick and the side wall facing the BASE tubes, is made of Nb±1Zr. The cell's colder structure, which includes the condenser structure, the interior thermal radiation shield, the casing and wick of the liquid sodium return artery and the side wall above the BASE tubes, is made of C-103. This niobium alloy is stronger and has a lower thermal conductivity than Nb±1Zr, reducing the parasitic heat conduction losses in the cell wall, hence enhancing the cell's performance. The base cell weighs 163.4 g and delivers 7 W e at 17% conversion e- ciency and load voltage of 3.3 V (cell speci®c mass of 23.4 g/W e ). These performance parameters were for TiN BASE electrodes characterized by B 75 AK 1=2 /m 2 Pa and G 50, assuming a BASE/electrode contact resistance of 0.06 X cm 2 and a BASE braze structure leakage resistance of 3 X. Also, the inner surfaces of the thermal radiation shield and the cell wall above the BASE tubes were covered with low emissivity rhodium. The temperatures of the BASE brazes and the evaporator were below the recom- mended design limits (1123 and 1023 K, respectively), and the temperature margin was P 20 K to avoid sodium condensation inside the BASE tube, shorting the cell. When high performance electrodes, char- acterized by B 120 A K 1=2 /m 2 Pa and G 10, were used, the cell's electric power increased to 8.38 W e at 3.5 V, and the eciency increased to 18.8%, decreasing the speci®c mass of the cell to 19.7 g/W e without exceeding any of the design temperature limits. Ó 2000 Elsevier Science Ltd. All rights reserved. Energy Conversion and Management 42 (2001) 721±739 www.elsevier.com/locate/enconman * Corresponding author. Tel.: +1-505-277-2813/+1-505-277-0446; fax: +1-505-277-2814/+1-505-277-0813. E-mail address: mgenk@unm.edu (M.S. El-Genk). 0196-8904/01/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved. PII:S0196-8904(00)00076-5