Capillary Limit of Evaporator Wick in Alkali Metal Thermal-to-Electric Converters

Vapor anode, multitube alkali metal thermal-to-electric converters are being developed for potential use in space and terrestrial electric power generation. In these converters, the capillary pressure head produced in the evaporator wick circulates the sodium working fluid. A two-dimensional, thermal-hydraulic model of the porous evaporator wick and of the liquid sodium return artery is developed and thermally coupled to an integrated model of a five-beta-alumina solid electrolyte (BASE) tube, stainless-steel sodium converter (PX-3A), and an eight-tube, Mo-41% Resodium converter. Results showed that the capillary limit in the evaporator wick of the PX-3A converter is reached at zero electrical current, when the thermal input power to the converter exceeds 16 W, or the hot-side temperature exceeds 1136 K. For the Mo-41%Re converter, these values are 22 W and 1150 K, respectively. Before reaching the capillary limit, however, two or more of the following temperature limits occurred in both converters: 1) the TiNi metal-ceramic braze joints' temperature exceeded 1123 K, 2) the evaporator wick surface temperature exceeded 1023 K, or 3) the temperature difference between the cold end of the BASE tubes and the evaporator wick surface was less than +20 K.

[1]  J. Tournier,et al.  An electric model of a vapour anode, multitube alkali–metal thermal-to-electric converter , 1999 .

[2]  S. Patankar.  Numerical Heat Transfer and Fluid Flow , 2018, Lecture Notes in Mechanical Engineering.

[3]  P. Cheng,et al.  Heat Transfer in Geothermal Systems , 1979 .

[4]  Mohamed S. El-Genk,et al.  Radiation heat transfer in multitube, alkali-metal thermal-to-electric converter , 1999 .

[5]  Michael G. Izenson,et al.  Condensation of sodium on a micromachined surface for AMTEC , 1993 .

[6]  Mohamed S. El-Genk,et al.  A transient model for liquid metal heat pipes , 1988 .

[7]  T. Cole,et al.  Thermoelectric Energy Conversion with Solid Electrolytes , 1983, Science.

[8]  Mohamed S. El-Genk,et al.  Analyses of static energy conversion systems for small nuclear power plants , 2003 .

[9]  Robert E. Apfel,et al.  The Tensile Strength of Liquids , 1972 .

[10]  E. Sparrow,et al.  Radiation Heat Transfer , 1978 .

[11]  Margaret A. K. Ryan,et al.  Metallurgical examination of an AMTEC unit , 2001 .

[12]  S. Chi.  Heat pipe theory and practice , 1976 .

[13]  Mohamed S. El-Genk,et al.  Performance analyses of an Nb–1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion cell , 2001 .

[14]  Mohamed S. El-Genk,et al.  Sodium vapor pressure losses in a multitube, alkali-metal thermal-to-electric converter , 1999 .

[15]  J. M. Delhaye,et al.  Jump conditions and entropy sources in two-phase systems , 1974 .