Performance analysis of cascaded thermoelectric converters for advanced radioisotope power systems

Advanced radioisotope power systems (ARPSs) for future planetary missions require higher conversion efficiency than the state-of-the-art (SOA) SiGe thermoelectric converter in order to decrease system mass and reduce mission cost. The performance of three cascaded thermoelectric converters (CTCs) for potential use in ARPSs is investigated at heat rejection temperatures of 375, 475 and 575 K and input thermal powers of 1, 2 and 3 Wth. These CTCs have top SiGe unicouples that are thermally, but not electrically, coupled to bottom unicouples having one of the following compositions: (a) TAGS-85 (p-leg) and 2N–PbTe (n-leg); (b) CeFe3.5Co0.5Sb12 (p-leg) and CoSb3 (n-leg); and (c) segmented p-leg of CeFe3.5Co0.5Sb12 and Zn4Sb3 and n-leg of CoSb3. The top and bottom unicouples in the CTCs are of the same length (10 mm), but the optimized cross-sectional areas of the n- and p-legs for maximum efficiency are different. The nominal hot junction temperature of the top SiGe unicouples at their peak efficiencies is 1273 K and that of the cold junction is 780 K when the bottom unicouple is of composition (a) and 980 K for compositions (b) and (c). The hot junction temperatures of the bottom unicouples are taken 20 K lower than the cold junctions of the top unicouples, but the input thermal powers to the former are the same as those rejected by the latter. Assuming zero side heat losses and a contact resistance of 150 μΩ cm2 per leg in the top and bottom unicouples, the calculated peak efficiencies of the CTCs vary from 9.43% to 14.35%. These efficiencies are 40–113% higher, respectively, than that of SOA SiGe (∼6.5%) when operating at the cold junction temperature of 566 K and the same hot junction temperature (1273 K) and contact resistance per leg. Decreasing this resistance to a realistic value of 50 μΩ cm2 per leg increases the peak efficiencies of the CTCs by 0.5–0.9 percentage points to 9.93–15.25%.

[1]  R. T. Carpenter.  Space nuclear power systems , 1972 .

[2]  David Buden,et al.  Space nuclear power , 1985 .

[3]  H.H. Saber,et al.  Predictions of segmented thermoelectric unicouples performance at hot temperatures /spl les/873 K and cold temperature of 298 K , 2002, Twenty-First International Conference on Thermoelectrics, 2002. Proceedings ICT '02..

[4]  A. Borshchevsky,et al.  High figure of merit in Ce-filled skutterudites , 1996, Fifteenth International Conference on Thermoelectrics. Proceedings ICT '96.

[5]  Mohamed S. El-Genk,et al.  Performance Tests of Skutterudites and Segmented Thermoelectric Converters , 2004 .

[6]  Mohamed S. El-Genk,et al.  Performance optimization of Segmented Thermoelectric Unicouples , 2002 .

[7]  Steven R. Oleson,et al.  Mission Steering Profiles of Outer Planetary Orbiters Using Radioisotope Electric Propulsion , 2004 .

[8]  Mohamed S. El-Genk,et al.  High efficiency segmented thermoelectric unicouple for operation between 973 and 300 K , 2003 .

[9]  Jean-Pierre Fleurial,et al.  High efficiency segmented thermoelectric unicouples , 2001 .

[10]  Mohamed S. El-Genk,et al.  SNPSAM - Space Nuclear Power System Analysis Model , 1987 .

[11]  Mohamed S. El-Genk,et al.  Cascaded Thermoelectric Conversion‐Advanced Radioisotope Power Systems (CTC‐ARPSs) , 2004 .

[12]  Mohamed S. El-Genk,et al.  Efficient segmented thermoelectric unicouples for space power applications , 2003 .

[13]  M.S. El-Genk,et al.  Energy conversion technologies for advanced radioisotope and nuclear reactor power systems for future planetary exploration , 2002, Twenty-First International Conference on Thermoelectrics, 2002. Proceedings ICT '02..

[14]  Richard Ewell,et al.  New materials and devices for thermoelectric applications , 1997, IECEC-97 Proceedings of the Thirty-Second Intersociety Energy Conversion Engineering Conference (Cat. No.97CH6203).

[15]  Toshio Fujita,et al.  Evoluation of SP-100 System Designs , 1994 .