Efficient segmented thermoelectric unicouples for space power applications

For the past 25 years, unicouples made of Silicon Germanium alloys (Si0.8Ge0.2 and Si0.63Ge0.38) have been used in the majority of the spacecraft powered by Radioisotope Thermoelectric Generators (RTGs) to explore various planets of the solar system as well as the sun. These unicouples operate typically at hot and cold side temperatures of 1175–1273 K and 573 K, respectively, converting the heat produced in the General Purpose Heat Source (GPHS) modules to electricity at efficiencies <7%. Recently, Segmented Thermoelectric Unicouples (STUs) made of n-type Bi2Te3 and CoSb3-based alloys and p-type Bi2Te3 and CeFe4Sb12-based alloys have been developed and tested successfully with a demonstrated efficiency to date of ∼10% and the potential for achieving 14–15% when operated at hot and cold side temperatures of 973 K and 300 K, respectively. This paper compares the performance of SiGe unicouples and skutterudite STUs, at same hot side temperature of 973 K and cold side temperatures of 300, 573, and 673 K, and the same total length and cross sectional dimensions of the p-leg. The area of the n-leg and the lengths of the segments of various materials in the STUs are determined based on maximizing either the electrical power density or the conversion efficiency. Results showed that replacing SiGe with skutterudite STUs in future radioisotope power systems (or even in conjunction with a space nuclear reactor and space probes), could increase the thermal to electric conversion efficiency at a heat source temperature of 973 K by ∼40% to 198% for Tc=673 K and 300 K, respectively. This would reduce by more than half the mass of the 238PuO2 fuel needed and the radiator’s surface area for rejecting the waste heat.

A three-dimensional model of Segmented Thermoelectric Unicouples (STUs) is developed and incorporated into the ANSYS commercial software. The governing equations are solved, subject to the prescribed boundary conditions, using the Finite Element Methodology (FEM) techniques and meshing capabilities in ANSYS. The model accounts for the side heat losses, handles different types of boundary conditions, and accounts for the non-homogeneity and the change in physical and thermoelectric properties of the segments materials in the n- and p-legs with temperature. The model predictions are compared with experimental data of two STUs, uni8 and uni12, comprised of n-type Bi2Te3 and CoSb3-based alloys and p-type Bi2Te3 and CeFe4Sb12-based alloys, and tested recently at the Jet Propulsion Laboratory (JPL) between hot and cold side temperatures of ∼305 K and 885 K, respectively. The calculations helped determine not only the side heat losses in these tests and the performance parameters of the STUs, but also the spatial dissipation of the heat losses from the various sides of and of the 3-D temperature fields in the n- and p-legs. The estimated values of the total side heat losses in uni8 and uni12 are 3.7 W and 1.83 W, respectively, and of the total contact resistance per leg are 146 and 690 μΩ-cm2, respectively. The predicted peak conversion efficiencies in these tests for uni8 and uni12 are 4.55% and 5.65%, respectively, compared to 11.46% and 9.09%, which could be attainable with zero side heat losses, for the same total contact resistance per leg.

The growth of pathogens potentially relevant to respiratory tract infection may be triggered by changes in ambient temperature. Few studies have examined the association between ambient temperature and pneumonia incidence, and no studies have focused on the susceptible elderly population. We aimed to examine the short-term association between ambient temperature and geriatric pneumonia and to assess the disease burden attributable to cold and hot temperatures in Hong Kong, China. Daily time-series data on emergency hospital admissions for geriatric pneumonia, mean temperature, relative humidity, and air pollution concentrations between January 2005 and December 2012 were collected. Distributed-lag nonlinear modeling integrated in quasi-Poisson regression was used to examine the exposure-lag-response relationship between temperature and pneumonia hospitalization. Measures of the risk attributable to nonoptimal temperature were calculated to summarize the disease burden. Subgroup analyses were conducted to examine the sex difference. We observed significant nonlinear and delayed associations of both cold and hot temperatures with pneumonia in the elderly, with cold temperatures having stronger effect estimates. Among the 10.7% of temperature-related pneumonia hospitalizations, 8.7% and 2.0% were attributed to cold and hot temperatures, respectively. Most of the temperature-related burden for pneumonia hospitalizations in Hong Kong was attributable to cold temperatures, and elderly men had greater susceptibility.

방사성동위원소 열전발전기는 장반감기 알파 혹은 베타 핵종에서 방출하는 하전입자를 차폐하여 방사선에너지를 열에너지로 전환하고 이때 발생하는 열전재료의 온도차를 이용하여 전력을 생산하는 시스템이다. 이 기술은 에너지 밀도가 높고 수명이 길며 신뢰성이 높아 우주개발, 국방 등 극한 환경에서 사용되는 장치, 센서 및 로봇 등의 에너지원으로 그 효용성이 매우 높다. 본 연구에서는 방사선 차폐해석 및 열전달 해석을 통하여 차폐체, 그리고 최대 온도구배를 가지는 열전재료의 형상과 배치를 결정하여 열전발전기 기초설계를 도출하였다.

Few studies have examined the attributable fraction (AF) of temperature to mortality and Years of Life Lost (YLL), especially in developing countries. This study aims to explore the short-term effect of the cold and hot temperatures on the cause-specific YLL and mortality, discover the attributable contributions from the temperature variations, and identify the vulnerable populations in Weifang, China. Daily registered death information and meteorological data over the period 2010-2016 were obtained in Weifang, a northern Chinese city. Generalized additive Poisson and Gaussian regression models were used to assess the impacts of temperatures on both mortality and YLL, explore the AF of the temperature variations on mortality, after adjusting for other covariates. Both hot and cold temperatures have had significant negative impacts on cause-specific mortality counts and YLL, with heat presented an acute and short effect and the cold temperatures had delayed effects and lasted for several days. In terms of the attributable fraction calculations, the contributions from cold effects was higher than that of hot effects on non-accidental, cardiovascular, and respiratory deaths (YLL 10.88 vs. 1.23%, 19.58 vs. 1.71%, and 14.47 vs. 3.05%; mortality 13.97 vs. 1.65%, 19.20 vs. 1.59%, and 14.89 vs. 3.09%), respectively. The elderly and women and people with low education level were the most vulnerable. The findings will provide important scientific evidences and policy implications for developing adaptation strategies to reduce the adverse effect of cold and hot exposure in Weifang, in terms of resource allocation, healthcare workforce capacity building, and community health education, especially for the vulnerable groups.

&lt;div class="htmlview paragraph"&gt;MOD-RTG represents the design configuration for the next generation of Radioisotope Thermoelectric Generators (RTG), aimed at improving specific power and efficiency over the current General Purpose Heat Source Radioisotope Thermoelectric Generator (GPHS-RTG). The modular RTG reference design has been described in previous papers (&lt;span class="xref"&gt;Reference 1&lt;/span&gt;). The multicouple is a key element required for the successful&lt;/div&gt; &lt;div class="htmlview paragraph"&gt; &lt;figure id="F1" class="figure"&gt; &lt;div class="graphic-wrapper"&gt;&lt;img class="article-figure figure" src="929482_fig0001.jpg" alt="No Caption Available"/&gt;&lt;/div&gt; &lt;/figure&gt; &lt;/div&gt; &lt;div class="htmlview paragraph"&gt;development of the modular RTG. The multicouple is a high voltage, thermoelectric device employing a close packed, glass bonded thermopile array of twenty thermoelectric couples, connected in a series circuit. The multicouple is designed to operate a 1270°K hot junction temperature and a 570°K cold junction temperature, yielding a power output of approximately 2.1 watts at 3.5 volts at beginning of life. The multicouple design (Reference &lt;span class="xref"&gt;Figure 1&lt;/span&gt; ) has also been described in a previous paper (&lt;span class="xref"&gt;Reference 2&lt;/span&gt;).&lt;/div&gt;

Cause-specific mortality attributable to cold and hot ambient temperatures in Hong Kong: a time-series study, 2006–2016

1. Alterations in dietary metabolisable energy (ME) concentration had a limited influence on food and nutrient intakes and egg mass output of hens in early lay kept at the prevailing air (10 degrees to 24 degrees C), cold (6 degrees to 16 degrees C) or hot (25 degrees to 35 degrees C) temperatures. 2. Energy intakes were not improved by increasing the dietary concentrations of nutrients other than energy. 3. At prevailing air and cold temperatures all dietary ME-nutrient density combinations allowed hens to meet the recommended daily protein intake but only hens fed the most concentrated diets were able to meet this recommendation at hot temperatures. 4. Even the highest intakes of ME and protein achieved at hot temperatures failed to increase egg mass output to the values attained on any diet at cold temperatures.

Laboratory studies on the mechanical properties of sulphur-based construction material at simulated Martian temperatures

Most adverse cardiovascular events are the result of an occlusive blood clot. During exercise, ischemic risk transiently increases, possibly due to exertion-related changes in coagulation and fibrinolytic activity. Previous research suggests ambient temperature affects resting coagulation and fibrinolytic potential, but the effect of heat and cold on hemostasis during exercise is unknown. PURPOSE: To assess changes in coagulation and fibrinolysis during maximal exercise in hot and cold temperatures, and to compare those responses to exercise under normal, temperate conditions. METHODS: Fifteen healthy male subjects (25.3 ± 4.3 years) completed maximal cycle ergometer exercise tests in hot (30°C), temperate (20°C) and cold (5° or 8° C) temperatures. Blood samples were obtained before and immediately after exercise and analyzed by ELISA to determine plasma concentrations of thrombin-antithrombin complex (TAT), tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1). Results were analyzed with a two-factor ANOVA using temperature and time (pre-, post-exercise) as within-subjects factors. Post-hoc pairwise comparisons were made using Fisher‘s LSD method. RESULTS: VO2peak was not different among the three temperatures (temperate = 40.7±8.7, hot = 41.8±9.4, cold = 41.2±9.2 ml/kg/min, p>0.05). A main effect of time was observed for TAT (temperate = 0.45±0.26 - 1.04±0.44 ng/ml, hot = 0.64±0.55 - 1.18±0.95 ng/ml, cold = 0.88±0.57 - 1.34±0.79 ng/ml, PRE to POST, respectively, p<0.01) and tPA activity (temperate = 0.72 ± 0.44 - 2.71±0.55 IU/ml, hot = 0.72±0.38 - 2.64±0.61 IU/ml, cold = 0.86±0.45 - 2.65±0.77 IU/ml, PRE to POST, respectively, p<0.01). A non-significant trend was observed for the PAI-1 response to exercise (temperate = 14.5±23.7 - 12.3±20.2 IU/ml, hot = 15.1±26.5 - 10.0±15.1 IU/ml, cold = 10.5±10.4 - 7.9±9.7 IU/ml, PRE to POST, respectively, p=0.08). Cold temperature resulted in significantly higher TAT concentrations than temperate conditions (p=0.05). No other main effects of temperature or time x temperature interactions were observed. CONCLUSIONS: The potential for clot formation is elevated during exposure to cold temperatures. These data suggest that risk of an ischemic event may be elevated in the cold.

Chapter Seventeen - Space nuclear power: Radioisotopes, technologies, and the future

To examine the associations between ambient temperature and hospitalizations for acute kidney injury (AKI) in Queensland, Australia, 1995–2016. Data were collected on a total of 34 379 hospitalizations for AKI from Queensland between 1 January 1995 and 31 December 2016. Meteorological data were downloaded from the Queensland Government’s Department of Environment and Science. We assessed the temperature-AKI relationship using a time-stratified case-crossover design fitted with conditional quasi-Poisson regression model and time-varying distributed lag non-linear model. Stratified analyses were performed by age, sex, climate zone and socioeconomic group. Both cold and hot temperatures were associated with hospitalizations for AKI. There were stronger temperature-AKI associations among women than men. Cold effects were only positive in the ⩾70 years age group. Hot effects were stronger in the ⩽59 years age group than in the >60 years age group. In different climate zone areas, cold effects decreased with increasing local mean temperatures, while hot effects increased. In different socio-economic status groups, hot effects were stronger in the poor areas than the affluent areas. From 1995 to 2016, the magnitude of associations between cold temperature and hospitalizations for AKI decreased, while the hot effect increased. The associations between hot temperature and hospitalizations for AKI become stronger, while the magnitude of cold effect decreased from 1995 to 2016. This trend may accelerate over the coming decades, which warrants further research. More attention is needed toward susceptible population including women, people ⩾70 years, and the people living in hot climate zones and in low socioeconomic status areas.

In this paper, we examine the utility of synthetic aperture radar (SAR) backscatter data to detect a change in snow water equivalent (SWE) over landfast first-year sea ice during winter at relatively cold temperatures. We begin by reviewing the theoretical framework for linking microwave scattering from SAR to the thermodynamic and electrical properties of first-year sea ice. Previous research has demonstrated that for a given ice thickness and air-temperature change, a thick snow cover will result in a smaller change in the snow-ice interface temperature than will a thin snow cover. This small change in the interface temperature will result in a relatively small change in the brine volume at the interface and the resulting complex permittivity, thereby producing a relatively small change in scattering. A thin snow cover produces the opposite effect-a greater change in interface temperature, brine volume, permittivity, and scattering. This work is extended here to illustrate a variation of this effect over landfast first-year sea ice using in situ measurements of physical snow properties and RADARSAT-1 SAR imagery acquired during the winter of 1999 in the central Canadian Archipelago at cold (~-26degC) and moderately cold (~-14degC) snow-sea-ice interface temperatures. We utilize in situ data from five validation sites to demonstrate how the change in microwave scattering covaries and is inversely proportional with the change in the magnitude of SWE. These changes are shown to be detectable over both short (2 days) and longer (45 days) time durations

Background: A number of studies have reported reductions in mortality risk due to heat and cold over time. However, questions remain about the drivers of these adaptation processes to ambient temperatures. We aimed to analyse the demographic and socioeconomic drivers of the downward trends in vulnerability to heat- and cold-related mortality observed in Spain during recent decades (1980-2018).Methods: We collected data on all-cause mortality, temperature and relevant contextual indicators for 48 provinces in mainland Spain and the Balearic Islands between Jan 1, 1980, and Dec 31, 2018. Fourteen contextual indicators were analysed representing ageing, isolation, urbanicity, heating, air conditioning (AC), house antiquity and ownership, education, life expectancy, macroeconomics, socioeconomics, and health investment. The statistical analysis was separately performed for the range of months mostly causing heat- (June-September) and cold- (October-May) related mortality. We first applied a quasi-Poisson generalised linear regression in combination with distributed lag non-linear models (DLNM) to estimate province-specific temperature-mortality associations for different periods, and then we fitted univariable and multivariable multilevel spatiotemporal meta-regression models to evaluate the effect modification of the contextual characteristics on heat- and cold-related mortality risks over time.Findings: The average annual mean temperature has risen at an average rate of 0&amp;#183;36&amp;#176;C per decade in Spain over 1980-2012, although the increase in temperature has been more pronounced in summer (0&amp;#183;40&amp;#176;C per decade in June-September) than during the rest of the year (0&amp;#183;33&amp;#176;C per decade). This warming has been observed, however, in parallel with a progressive reduction in the mortality risk associated to both hot and cold temperatures. We found independent associations for AC with heat-related mortality, and heating with cold-related mortality. AC was responsible for about 28&amp;#183;6% (31&amp;#183;5%) of the decrease in deaths due to heat (extreme heat) between 1989-1993 and 2009-2013, and heating for about 38&amp;#183;3% (50&amp;#183;8%) of the reductions in deaths due to cold (extreme cold) temperatures. Ageing (ie, proportion of population over 64 years) attenuated the decrease in cold-related mortality.Conclusion: AC and heating are effective societal adaptive measures to heat and cold temperatures. This evidence holds important implications for climate change health adaptation policies, and for the projections of climate change impacts on human health.

Characteristics and expression of genes encoding two small heat shock protein genes lacking introns from Chilo suppressalis.