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Mohamed S. El-genk - One of the best experts on this subject based on the ideXlab platform.
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Effects of metallic coatings on the performance of skutterudite-based segmented unicouples
Energy Conversion and Management, 2007Co-Authors: Hamed H. Saber, Mohamed S. El-genkAbstract:Abstract An analytical model is developed to investigate the effects of applying thin metallic coatings on the legs of skutterudite based thermoelectric unicouples and to calculate the impact on the dimensions and the performance parameters of the unicouple. These coatings suppress the sublimation of antimony from the legs near the Hot Junction (∼973 K) and, hence, minimize the degradation in the unicouple performance with operation time. Coating materials investigated are: tantalum (Ta), titanium (Ti), molybdenum (Mo) and vanadium (V), which have different thermal conductivities, electrical resistivities, coefficients of thermal expansion (CTE) and vapor pressures. Detailed comparison of these coating materials was necessary since none clearly satisfies both a minimal decrease in the performance of the unicouple and ease of fabrication and long life. The former favors low thermal conductivity and high electrical resistivity, while the latter favors low CTE and low vapor pressure. The lengths of the coatings of both the n- and p-legs, which were found to be different for best unicouple performance, are determined as functions of the antimony vapor pressure off the exposed portions of the legs, which varied from 1.0 to 1000 mPa, and the thickness of the applied metallic coating (1–9 μm). Results indicated that increasing the coating thickness decreases the conversion efficiency but increases the load electrical power of the unicouple. Despite their high CTE, Ti or V coatings are best in terms of the effect on the unicouple performance when a coating thickness >1 μm in needed. They cause the smallest decreases, while Ta or Mo coating with lower CTEs, result in the largest decreases in the conversion efficiency. With thin coatings (⩽1 μm), however, the effects on conversion efficiency and electrical power of the unicouple are significantly small. In this case, a Mo coating would be best since it has the smallest CTE and low vapor pressure.
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Performance analysis of cascaded thermoelectric converters for advanced radioisotope power systems
Energy Conversion and Management, 2005Co-Authors: Mohamed S. El-genk, Hamed H. SaberAbstract: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%.
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Performance Test Results of a Skutterudite‐Based Unicouple with a Metallic Coating
AIP Conference Proceedings, 2005Co-Authors: Hamed H. Saber, Mohamed S. El-genk, Thierry CaillatAbstract:A performance test of a Skutterudite‐based unicouple (MAY‐04) with a metallic coating to suppress the sublimation of antimony from the legs near the Hot Junction is performed in vacuum (∼ 9 ×10−7 torr) for ∼ 2,000 hours at Hot and cold Junction temperatures of 892.1 ± 11.9 K and 316.1 ± 5.5 K, respectively. The p‐leg is made of CeFe3.5Co0.5Sb12 and the n‐leg is made of CoSb3. Presented are the measured voltage‐current characteristics, electrical power, open‐circuit voltage, and the Seebeck coefficients of the legs as functions of cumulative test time. Also presented is the estimate of the conversion efficiency, ∼ 96 hrs after the start of test. To demonstrate the effectiveness of the metallic coating, the measurements for MAY‐04 are compared with those of two uncoated unicouples of the same leg materials (MAR‐03 and JUN‐03), which had been tested earlier. The cross‐sectional areas of the legs in MAY‐04 are larger than those in MAR‐03 and JUN‐03, tested in argon cover gas at ∼ 0.051–0.068 MPa for 450 and 1...
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Performance of a Skutterudite-based Segmented Unicouple with a Metallic Coating Near Hot Junction
AIP Conference Proceedings, 2005Co-Authors: Hamed H. Saber, Mohamed S. El-genkAbstract:Skutterudite‐based thermoelectric unicouples are currently being considered for use in next generation Radioisotope Power Systems (RPSs) to reduce the amount of 238PuO2 fuel and the mission’s cost and increase the system specific power. In these unicouples, typically operateing at a Hot Junction temperature of 973K, the loss of the volatile antimony from the n‐ and p‐legs near the Hot Junction, if not suppressed, could gradually degrade their performance. Recently, it has been shown that such a loss of antimony could be effectively suppressed by applying a thin metallic coating on the legs near the Hot Junction. However, to minimize the impact on the conversion efficiency, the thickness and the length of the coating need to be optimized. An analytical model for coated skutterudite‐based segmented unicouples is developed and used to optimize the length and thickness of the coating and quantity its effect on the conversion efficiency and load electrical power. Several coating materials are investigated: Tan...
Hamed H. Saber - One of the best experts on this subject based on the ideXlab platform.
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Effects of metallic coatings on the performance of skutterudite-based segmented unicouples
Energy Conversion and Management, 2007Co-Authors: Hamed H. Saber, Mohamed S. El-genkAbstract:Abstract An analytical model is developed to investigate the effects of applying thin metallic coatings on the legs of skutterudite based thermoelectric unicouples and to calculate the impact on the dimensions and the performance parameters of the unicouple. These coatings suppress the sublimation of antimony from the legs near the Hot Junction (∼973 K) and, hence, minimize the degradation in the unicouple performance with operation time. Coating materials investigated are: tantalum (Ta), titanium (Ti), molybdenum (Mo) and vanadium (V), which have different thermal conductivities, electrical resistivities, coefficients of thermal expansion (CTE) and vapor pressures. Detailed comparison of these coating materials was necessary since none clearly satisfies both a minimal decrease in the performance of the unicouple and ease of fabrication and long life. The former favors low thermal conductivity and high electrical resistivity, while the latter favors low CTE and low vapor pressure. The lengths of the coatings of both the n- and p-legs, which were found to be different for best unicouple performance, are determined as functions of the antimony vapor pressure off the exposed portions of the legs, which varied from 1.0 to 1000 mPa, and the thickness of the applied metallic coating (1–9 μm). Results indicated that increasing the coating thickness decreases the conversion efficiency but increases the load electrical power of the unicouple. Despite their high CTE, Ti or V coatings are best in terms of the effect on the unicouple performance when a coating thickness >1 μm in needed. They cause the smallest decreases, while Ta or Mo coating with lower CTEs, result in the largest decreases in the conversion efficiency. With thin coatings (⩽1 μm), however, the effects on conversion efficiency and electrical power of the unicouple are significantly small. In this case, a Mo coating would be best since it has the smallest CTE and low vapor pressure.
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Performance analysis of cascaded thermoelectric converters for advanced radioisotope power systems
Energy Conversion and Management, 2005Co-Authors: Mohamed S. El-genk, Hamed H. SaberAbstract: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%.
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Performance Test Results of a Skutterudite‐Based Unicouple with a Metallic Coating
AIP Conference Proceedings, 2005Co-Authors: Hamed H. Saber, Mohamed S. El-genk, Thierry CaillatAbstract:A performance test of a Skutterudite‐based unicouple (MAY‐04) with a metallic coating to suppress the sublimation of antimony from the legs near the Hot Junction is performed in vacuum (∼ 9 ×10−7 torr) for ∼ 2,000 hours at Hot and cold Junction temperatures of 892.1 ± 11.9 K and 316.1 ± 5.5 K, respectively. The p‐leg is made of CeFe3.5Co0.5Sb12 and the n‐leg is made of CoSb3. Presented are the measured voltage‐current characteristics, electrical power, open‐circuit voltage, and the Seebeck coefficients of the legs as functions of cumulative test time. Also presented is the estimate of the conversion efficiency, ∼ 96 hrs after the start of test. To demonstrate the effectiveness of the metallic coating, the measurements for MAY‐04 are compared with those of two uncoated unicouples of the same leg materials (MAR‐03 and JUN‐03), which had been tested earlier. The cross‐sectional areas of the legs in MAY‐04 are larger than those in MAR‐03 and JUN‐03, tested in argon cover gas at ∼ 0.051–0.068 MPa for 450 and 1...
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Performance of a Skutterudite-based Segmented Unicouple with a Metallic Coating Near Hot Junction
AIP Conference Proceedings, 2005Co-Authors: Hamed H. Saber, Mohamed S. El-genkAbstract:Skutterudite‐based thermoelectric unicouples are currently being considered for use in next generation Radioisotope Power Systems (RPSs) to reduce the amount of 238PuO2 fuel and the mission’s cost and increase the system specific power. In these unicouples, typically operateing at a Hot Junction temperature of 973K, the loss of the volatile antimony from the n‐ and p‐legs near the Hot Junction, if not suppressed, could gradually degrade their performance. Recently, it has been shown that such a loss of antimony could be effectively suppressed by applying a thin metallic coating on the legs near the Hot Junction. However, to minimize the impact on the conversion efficiency, the thickness and the length of the coating need to be optimized. An analytical model for coated skutterudite‐based segmented unicouples is developed and used to optimize the length and thickness of the coating and quantity its effect on the conversion efficiency and load electrical power. Several coating materials are investigated: Tan...
Wen Bao - One of the best experts on this subject based on the ideXlab platform.
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Performance evaluation of waste heat recovery systems based on semiconductor thermoelectric generators for hypersonic vehicles
Energies, 2017Co-Authors: Kunlin Cheng, Chuanwen Lv, Jiang Qin, Silong Zhang, Yu Feng, Wen BaoAbstract:The types and the characteristics of the waste heat on hypersonic vehicles and the application feasibility of thermoelectric generators (TEGs) for hypersonic aircraft are discussed in this paper. Two thermoelectric generator schemes with an isothermal heat source and a variable temperature heat source were proposed, and the corresponding models were developed to predict the performance of the waste heat recovery systems on a hypersonic vehicle with different heat sources. The thermoelectric efficiency variation with electric current, the temperature distribution of fuel and Junctions, and the distribution of the thermoelectric figure of merit (ZT value) are described by diagrams. Besides, some improvements for a better performance are analyzed. The results indicate that the maximum values of thermoelectric efficiency are 5% and 2.5% for the isothermal heat source and the variable temperature heat source, respectively, and the thermoelectric efficiency improves with the temperature of the Hot Junction. The performance of the TEGs with variable temperature heat source is worse than that of the other TEGs under the same highest Hot Junction temperature conditions, and the former has a better conversion efficiency than the latter when the average temperatures are identical.
Kendall Rutledge - One of the best experts on this subject based on the ideXlab platform.
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experimental and theoretical study of uncertainty in pyranometers for surface radiation
Remote Sensing, 1999Co-Authors: Amie Smith M Neste, Martial Haeffeli, Robe J Maha, Feli J Nevarez, Seiji Kato, Kendall RutledgeAbstract:The Eppley pyranometer is widely used to measure shortwave irradiances. This instrument consists of a blackened surface in intimate thermal contact with the Hot Junction of a thermopile. The cold Junction of the thermopile is in thermal contact with a heat sink. Shortwave radiation transmitted through two concentric hemispherical domes is absorbed by the blackened surface. The voltage developed by the thermopile is then interpreted in terms of the shortwave irradiance. Measurements obtained using these instruments are known to be influenced by thermal radiation that produces an offset from the signal that would result solely from the incident shortwave radiation. The thermal radiation emitted and reflected by the filters modifies the net radiation at the detector surface. The ongoing efforts to model these exchanges and to use experimental results to verify the model are described. The parallel experimental effort consists of determining the sensitivity of instrument response to thermal radiation effects. In this effort, thermistors are used to characterize the thermal gradients responsible for the instrument offset. The ultimate goal of the work described is to provide reliable protocols, based on an appropriate instrument model, for correcting measured SW irradiance for variable thermal radiation effects.
Kunlin Cheng - One of the best experts on this subject based on the ideXlab platform.
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Performance evaluation of waste heat recovery systems based on semiconductor thermoelectric generators for hypersonic vehicles
Energies, 2017Co-Authors: Kunlin Cheng, Chuanwen Lv, Jiang Qin, Silong Zhang, Yu Feng, Wen BaoAbstract:The types and the characteristics of the waste heat on hypersonic vehicles and the application feasibility of thermoelectric generators (TEGs) for hypersonic aircraft are discussed in this paper. Two thermoelectric generator schemes with an isothermal heat source and a variable temperature heat source were proposed, and the corresponding models were developed to predict the performance of the waste heat recovery systems on a hypersonic vehicle with different heat sources. The thermoelectric efficiency variation with electric current, the temperature distribution of fuel and Junctions, and the distribution of the thermoelectric figure of merit (ZT value) are described by diagrams. Besides, some improvements for a better performance are analyzed. The results indicate that the maximum values of thermoelectric efficiency are 5% and 2.5% for the isothermal heat source and the variable temperature heat source, respectively, and the thermoelectric efficiency improves with the temperature of the Hot Junction. The performance of the TEGs with variable temperature heat source is worse than that of the other TEGs under the same highest Hot Junction temperature conditions, and the former has a better conversion efficiency than the latter when the average temperatures are identical.