High-temperature Power Generation Research Articles

Comparative performance analysis of recuperative helium and supercritical CO₂ Brayton cycles for high-temperature energy systems

This study presents a comprehensive comparative analysis of recuperative Brayton cycles utilizing helium (He) and supercritical carbon dioxide (sCO2) as working fluids for high-temperature power generation, focusing on applications in next-generation concentrated solar power (CSP) systems. Thermodynamic cycle simulations were conducted across a temperature range of 1000 K–2000 K, exploring the effects of low-side pressure (1 bar–100 bar) and expansion ratio (1–5) on key performance indicators. These indicators included thermal efficiency, net specific work output, mass flow rate, volumetric flow rate, and system irreversibilities. Results demonstrate that helium-based Brayton cycles exhibit superior thermal efficiency at high temperatures, reaching up to 65 %, compared to sCO2 cycles, which achieve efficiencies up to 55 %. This advantage stems from helium's higher specific heat capacity and lower pressure drops within the cycle. Conversely, sCO2 cycles demonstrate higher net specific work output due to the fluid's higher density, leading to more compact turbomachinery. The study further investigates the impact of irreversibilities, including pressure losses, leakage losses, and heat transfer losses, on cycle performance. A detailed analysis of multi-stage Brayton cycles incorporating intercoolers and reheaters reveals the potential for further efficiency enhancements in both helium and sCO2 systems. This research provides valuable insights for the design and optimization of high-temperature power generation systems, particularly for next-generation CSP plants. The findings highlight the trade-offs between working fluid properties and cycle configurations, guiding the selection of optimal solutions based on specific application requirements and operating conditions.

The thermal shock resistance of in-situ synthesized mullite absorption and storage integrated ceramics for solar thermal power generation

Solar high-temperature thermal power generation systems require thermal storage materials with excellent thermal shock resistance due to the large temperature difference during operation (in the range of 20–800 °C). In this study, mullite-based absorption and storage integrated ceramics were prepared using low-cost bauxite and kaolin as raw materials and Fe2O3 as additive. The effect of Fe2O3 on the thermal shock resistance of mullite-based ceramics was investigated. The results showed that the absorption and bending strength of sample BK4 (bauxite: 50 wt%, kaolin: 50 wt%, Fe2O3: additional 11 wt%) increased by 2.98% (89.8%) and 8.00% (147.10 MPa), with a storage thermal density of 1185.75 kJ kg−1 after 30 thermal shock cycles. The mechanism for the excellent thermal shock resistance of the ceramics is revealed from the aspect of the changes in phase and microstructure of the samples induced by the changes in the mass transfer rate during the thermal shock process. It was calculated that a unit volume of BK4 (with a raw material cost of about 154.22 USD) could generate 974.95 kW h of electricity (saving 119.92 kg of coal) when used in a solar thermal storage system.

A first-principles assessment of the thermoelectric properties in half-heusler compound NbIrSn

Converting waste heat into electric power using thermoelectric materials could significantly address global energy needs. Half-Heusler compounds exhibit significant promise as thermoelectric materials suitable for high temperatures, thereby offering a potential solution to address the energy crisis. By employing density functional theory (DFT), semi-classical Boltzmann transport theory (BTE), and density functional perturbation theory (DFPT), this study thoroughly examines the structural, electronic, magnetic, phonon, mechanical, and thermoelectric properties of 18 valence electron half Heusler compound NbIrSn. Considering the presence of heavy 5d transition element Ir in our compound, all calculations are carried out with and without spin–orbit coupling (SOC). This material display both dynamic and mechanical stability, and also possess the property of ductility as indicated by Pugh’s ratio and Poisson’s ratio. NbIrSn is identified as non-magnetic semiconductors with indirect band gaps of 0.65 eV and it reduces to 0.63 eV when SOC is included. The different transport parameters are analyzed in relation to the chemical potential and doping concentrations for different temperatures. The lattice thermal conductivity of the material at room temperature is measured to be 13.40 Wm−1K−1 and 14.81 Wm−1K−1without and with SOC respectively. The optimal zT values for NbIrSn at 1200 K are 0.98 with p-type doping and 0.31 with n-type doping. Incorporating SOC leads to a substantial improvement, raising the optimal zT values to 1.33 for p-type doping and 0.47 for n-type doping. In conclusion, incorporating SOC is essential when analyzing the characteristics of the proposed compound. The present study highlights NbIrSn as a potentially a favorable candidate for p-type doping on high-temperature power generation.

High-temperature oxidation mechanism of ZrCoSb-based half-Heusler thermoelectric compounds

ZrCoSb-based half-Heusler (HH) compounds are among the most promising thermoelectric (TE) materials for high-temperature power generation. Oxidation resistance is one of the key issues for realizing the practical application of TE materials for long-term service in the ambient working environment. In this work, the oxidation behavior of Zr0.5Hf0.5CoSb0.8Sn0.2 (ZHCSS) half-Heusler is systematically studied in the service temperature range from 873 to 1073 K. It is revealed that three typical layers of oxidation products tend to form on the surface of HH sample, namely, the dense oxide layer (DOL) composed of (Zr,Hf)O2 and CoSb, the alternate oxide layer (AOL) composed of repeated (Zr,Hf)O2 and CoSb2O6/Co3O4, and the CoSb layer between the DOL and AOL. The mass gain during oxidation is mainly caused by the rapid growth of AOL, which is controlled by the outward diffusion of Zr/Hf and the inward diffusion of oxygen. The formation of a continuous CoSb layer and DOL is found beneficial to block the outward diffusion of Zr/Hf. Based on the analysis of the dominant factors on the outward and inward diffusions as well as the reaction activation energy, a simple approach is proposed to improve the oxidation resistance of Zr0.5Hf0.5CoSb0.8Sn0.2 by pre-oxidizing the sample in low oxygen pressure to form the dense (Zr,Hf)O2 and CoSb layers as oxidation protecting and/or diffusion blocking layers. The oxidation test shows the effectiveness of such pre-oxidation on the formation and growth of the AOL and therefore on improving the service stability of Zr0.5Hf0.5CoSb0.8Sn0.2 at high temperatures in the air.

Synthesis and thermoelectric properties of Cr-substituted higher manganese silicides prepared by pack cementation

Higher manganese silicides are attractive low-cost thermoelectric materials finding application in middle to high-temperature power generation. However, for practical use their performance needs to be enhanced. Pack cementation is a simple, green and economic method applied so far on the preparation of pure thermoelectric metal silicide powders. In this study, pack cementation is employed for the synthesis of doped thermoelectric powder for the first time as a promising single-step process. Compounds Mn1-xCrxSi1.80 (0.02≤x ≤ 0.15) at which Cr substitutes Mn site in the matrix are prepared and examined regarding their composition, microstructure and performance. Considerable amounts of CrSi2 impurity are present for x ≥ 0.07. The highest thermoelectric efficiency is achieved for Cr 4% substitution of Mn leading to the peak figure of merit ZTmax=0.59 at 814 K (∼35% enhancement). The measured oxidation resistance in this temperature region is high. Pack cementation has been successfully utilized to synthesize high-performance Cr-substituted higher manganese silicide powder.

Optical Design and Performance Analysis of the Medium Temperature Parabolic Trough Collector by Simulation Method

The parabolic trough heat collection technology was mainly used in the field of high-temperature power generation, and there was less research on the application of medium temperature heat utilization. In view of the huge heat demand in the medium temperature range (120°C-240°C) in the industrial field, trough solar thermal technology for the medium temperature heat energy recovery have unique technical advantages and wide perspective applications. In this study, based on the meteorological resources of Ejina Banner (Inner Mongolia Autonomous Region) and the heat demand, we propose a design for small sized parabolic trough collector, aperture width is 2.55m, focal length is 0.721m, and rim angle is 83°. The optical efficiency of this collector is 77.05% calculated by Monte Carlo ray tracing (MCRT) method, and the heat flux intensity distribution of the collector is simulated by the Soltrace. Finally, the results can provide some support and technical references for the medium temperature application.

Solid Oxide Fuel Cell-Based Polygeneration Systems in Residential Applications: A Review of Technology, Energy Planning and Guidelines for Optimizing the Design

Solid oxide fuel cells are an emerging energy conversion technology suitable for high-temperature power generation with proper auxiliary heat. Combining SOFCs and polygeneration has produced practical applications for modern energy system designs. Even though many researchers have reviewed these systems’ technologies, opportunities and challenges, reviews regarding the optimal strategy for designing and operating the systems are limited. Polygeneration is more complicated than any other energy generation type due to its ability to generate many types of energy from various prime movers. Moreover, integration with other applications, such as vehicle charging and fueling stations, increases the complication in making the system optimally serve the loads. This study elaborates on the energy planning and guidelines for designing a polygeneration system, especially for residential applications. The review of polygeneration technologies also aligns with the current research trend of developing green technology for modern and smart homes in residential areas. The proposed guideline is expected to solve the complication in other applications and technologies and design the polygeneration system optimally.

Discovery of YbNiSb-Based Half-Heusler Alloys as Promising Thermoelectric Materials

Half-Heusler materials are promising candidates for high-temperature power generation and have relatively high lattice thermal conductivity compared to other thermoelectric material systems. In this work, we report novel p-type YbNiSb-based half-Heusler alloys with a low lattice thermal conductivity (∼3.6 W m–1 K–1 at 340 K) that resulted from their large Grüneisen parameter, low sound speed, and low Debye temperature. All YbNiSb-based alloys exhibit a high carrier mobility of 30–50 cm2 V–1 s–1 at room temperature because of their relatively small effective mass. Importantly, the structural analysis reveals that Yb-rich Yb1.3Ni0.9Sb0.8 exhibits Yb/Ni and Yb/Sb substitution, indicating a wide homogeneity region of the YbNiSb phase experimentally. The adjustable Yb and Ni contents in YbNiSb-based alloys can modify the band structure around the Fermi level and significantly affect electrical transport properties. Additionally, by doping Ta at Yb sites, the carrier concentration and lattice thermal conductivity of these alloys can be manipulated. Consequently, a peak zT value of 0.45 at 823 K was achieved for Yb0.95Ta0.05NiSb. Our work demonstrates that YbNiSb-based alloys are promising p-type thermoelectric materials and suggests the possibility of exploring novel thermoelectric alloys in rare-earth nickel pnictides via tuning their composition and crystal structure.

Study of thermoelectric performance and intrinsic defect of promising n-type half-Heusler FeGeW

Half-Heusler (HH) compounds are considered promising thermoelectric materials for high-temperature power generation due to their good electrical properties and thermal stability. Some new HHs with excellent thermoelectric properties are found to be p-type, the discovery of competitive n-type HH materials has been extremely challenging. Here, we report a new HH compound FeGeW through first-principles calculation, which exhibits a high ZT of 2.36 at 1000 K. Systematically studied its thermoelectric performance indicates that a large dispersion or small band effective mass of conduction band can efficiently improve the electrical conductivity of n-type FeGeW. From the calculated formation energy of intrinsic point defects, we find that positive charged Fe interstitial are found to be the dominant defect at Fe-rich/Ge-poor condition, which account for the n-type conduction. Moreover the transition levels of Fe interstitial defect is shallow, which means that this donor defect does not damage electrical conductivity and thermoelectric performance. These results not only find a new n-type HH compound FeGeW, but also are helpful for understanding the roles of point defects in FeGeW, which is expected to encourage more experimental and theoretical investigations to study this kind of n-type HH thermoelectric material and seek out strategies to optimize thermoelectric performance using intrinsic point defect.

Refractory All-Ceramic Thermal Emitter for High-Temperature Near-Field Thermophotovoltaics

Thermophotovoltaics is a promising technology for heat recovery and has garnered tremendous attention in the last decades. This work theoretically evaluates the performance of a thermophotovoltaic system equipped with refractory all-ceramic selective thermal emitters made of boron carbide, silicon carbide and beryllium oxide for a high working temperature of 2000 ∘C, which corresponds to the external quantum efficiency of a SiC/Si tandem cell. The influence of thickness and filling ratio on the emissivity of thermal emitters over the wavelength ranging from 0.2 μm to 2.5 μm is studied. The corresponding spectral heat flux and output power are analyzed as well. For a specific configuration, the parameters for the thermophotovoltaic system are obtained, including short circuit current, open circuit voltage, fill factor, total heat flux, output power and conversion efficiency. The proposed all-ceramic thermal emitter ensures the robustness in the high-temperature working condition due to its thermal stability. The tuning of emissivity is achieved and analyzed based on distinct emitter nanostructures, and the further influence on the thermophotovoltaic system performance is deeply explored. This work sheds light on research of high-temperature thermal management and power generation.

A sliding-bed particle solar receiver with controlling particle flow velocity for high-temperature thermal power generation

Various impeded flow particle receivers were proposed to prolong the particle residence time but always faced the risk of thermal deterioration and the difficulty of real-time particle velocity control. Herein, we reported a novel impeded flow particle receiver to solve above problems and further have the potential to control the particle velocity distribution, which could provide a heat source with better stability, better uniformity and higher temperature for subsequent thermal power generation and other thermal applications. In this receiver, the friction along the path and the gate valves at outlet act as the obstruction structures to allow the particles to move slowly and controllably in the form of a sliding-bed, which is why we call this receiver a sliding-bed receiver. The sliding-bed receiver's structural validity and operational characteristics at different working conditions were detailly investigated with both experimental and numerical methods. Experimental results showed that the outlet particle temperature and efficiency could reach 847 °C and 77.2% under a solar simulator of 4 kW. An optical and thermal coupling model was developed and revealed an improved particle temperature of 1350 °C and efficiency of 82% under higher incident power. The effects of the effects of the incident power distribution, the particle velocity distribution and the quartz glass on aperture on the receiver performance were detailly analyzed, which could also help optimize the design and operation of other particle receivers such as free-falling particle receivers.

Conformal High-Power-Density Half-Heusler Thermoelectric Modules: A Pathway toward Practical Power Generators.

Thermoelectric generators (TEGs) exploiting the Seebeck effect provide a promising solution for waste heat recovery. Among the large number of thermoelectric (TE) materials, half-Heusler (hH) alloys are leading candidates for medium- to high-temperature power generation applications. However, the fundamental challenge in this field has been inhomogeneous material properties at large wafer diameters, insufficient power output from the modules, and rigid form factors of TE modules. This has restricted the transition of TEGs in practical applications for over three decades. Here, we successfully demonstrate large diameter wafers with uniform TE properties, high-power conformal hH TE modules for high-temperature application, and their direct integration on flue gas platforms, such as cylindrical tubes, to form large area flexible TEGs. This new conformal architecture design provides a breakthrough toward medium-/high-temperature TEGs over the conventional BiTe- and polymer-based flexible TEG design. A variable fill factor and greater flexibility due to the conformal design result in higher device performance as compared to conventional rigid TEG devices. Modules with 72-couple hH legs exhibit a device high-power-density of 3.13 W cm-2 and a total output power of 56.6 W under a temperature difference of 570 °C. These results provide a promising pathway toward widespread utilization of thermoelectric technology into the waste heat recovery application and will have a significant impact on the development of practical thermal to electrical converters.

Selective Enhancement in Phonon Scattering Leads to a High Thermoelectric Figure-of-Merit in Graphene Oxide-Encapsulated ZnO Nanocomposites.

ZnO is a promising candidate for use as an environmentally friendly thermoelectric (TE) material. However, high thermal conductivity leading to a poor TE figure-of-merit (zT) needs to be addressed to achieve a significant TE efficiency for commercial applications. Here, we demonstrate that selective enhancement in phonon scattering leads to an increase in the zT of ZnO because of Al doping and reduced graphene oxide (RGO) encapsulation. These nanocomposites are synthesized via a facile and scalable method. The incorporation of 1 at% Al with 1.5 wt % RGO into ZnO has been found to show significant improvement in zT (0.52 at 1100 K), which is an order of magnitude larger compared to that of bare undoped ZnO. Photoluminescence and X-ray photoelectron spectroscopy measurements confirm that RGO encapsulation significantly quenches surface oxygen vacancies in ZnO along with nucleation of new interstitial Zn donor states. Tunneling spectroscopy performed on bare as well as composite particles reveals that the band gap of ∼3.4 eV for bare ZnO reduces effectively to ∼0.5 eV upon RGO encapsulation, facilitating charge transport. The electrical conductivity also benefits from high densification (>95%) achieved using the spark plasma sintering method, which also aids in reduction of graphene oxide into RGO. The same Al doping and RGO capping synergistically bring about drastic reduction of thermal conductivity, through enhanced interfacial and point-defect-phonon scatterings. These opposing effects on electrical and thermal conductivities lead to enhancement in the power factors as well as the zT value. Overall, a practically viable route has been demonstrated for the synthesis of oxide-RGO TE materials, which could find their potential applications in high-temperature TE power generation.

A machine learning aided interpretable model for rupture strength prediction in Fe-based martensitic and austenitic alloys

The class of 9–12% Cr ferritic-martensitic alloys (FMA) and austenitic stainless steels have received considerable attention due to their numerous applications in high temperature power generation industries. To design high strength steels with prolonged service life requires a thorough understanding of the long-term properties, e.g., creep rupture strength, rupture life, etc., as a function of the chemical composition and processing parameters that govern the microstructural characteristics. In this article, the creep rupture strength of both 9–12% Cr FMA and austenitic stainless steel has been parameterized using curated experimental datasets with a gradient boosting machine. The trained model has been cross validated against unseen test data and achieved high predictive performance in terms of correlation coefficient (R^{2} > 0.98 for 9–12% Cr FMA and R^{2} > 0.95 for austenitic stainless steel) thus bypassing the need for additional comprehensive tensile test campaigns or physical theoretical calculations. Furthermore, the feature importance has been computed using the Shapley value analysis to understand the complex interplay of different features.

Pursuit of thermoelectric properties in L21 structured Co2PAl (P = Ru, Rh) ductile ferromagnetic materials: A first principles prospective

Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. The capability of Heusler alloys to provide the intriguing concerns mainly on the physical properties with specific variations has prolonged their ability to thermoelectric technology. In the light of current study, we investigate the structural, elasto-mechanical and thermoelectric-transport properties of Co2PAl (P = Ru, Rh) materials within the framework of the density functional theory and semi classical Boltzmann transport approach. The structural composition demonstrates cubic crystalline geometry of these alloys. Elastic constants (like Pugh’s ratio, Cauchy pressure etc.) display that the present set of alloys are mechanically stable possessing ductile nature with high melting temperature. Based on the thermal and elasto-mechanical stability, the Debye temperatures of Co2PAl Heuslers are 337.53K and 472.89K respectively. Thermoelectric transport coefficients are predicted using the Boltzmann transport theory under constant relaxation approximation, where Seebeck coefficient (S), total thermal conductivity, power factor and figure of merit are calculated. The electrical conductivity is high mainly due to high carrier mobility, while total thermal conductivity is moderate due to low lattice thermal conductivity. The calculated PF (zT) for Co2RhAl is 0.90 ​× ​10−5 ​W/mK2 (0.37) at 800K and for Co2RuAl is 0.85 ​× ​10−5W/mK2 (0.34) at 800K temperature. The calculated figures of merit recommend that these alloys have a potential thermoelectric applicability for high temperature power generation. Present study shows a significant value of Seebeck coefficient, power factor and zT values along with ductile nature illustrate the consequence applications in research fields like energy harvesting and thermoelectrics technology.

Exploring thermoelectric properties and stability of half-Heusler PtXSn (X = Zr, Hf) semiconductors: A first principle investigation

Half-Heuslers (HH) have found ever-increasing popularity as high temperature thermoelectric (TE) materials. In this paper, the electron and phonon transport equations are solved to understand the thermoelectric character of the PtXSn (X = Zr, Hf) compounds. Here, we have elucidated the phonon stability, electronic properties, thermoelectric response from lattice thermal conductivity, and phonon dependent parameters. The PtXSn compounds reveal an indirect bandgap semiconducting nature with a gap of 1.23 eV and 0.94 eV for PtZrSn and PtHfSn, respectively. At room temperature, a low magnitude of lattice thermal conductivity (κl) for PtZrSn (16.96 W/mK) and PtHfSn (10.04 W/mK) compounds is observed. The calculated maximum value of ZT is 0.57 and 0.24 observed for PtHfSn and 0.24 PtZrSn, respectively. Our present investigation demonstrate that the PtHfSn compound is potentially a favorable candidate for high-temperature power generation.

Accelerated Development of Refractory Nanocomposite Solar Absorbers using Bayesian Optimization

ABSTRACTMachine learning-based approach is desired for accelerating materials design, development and discovery in combination with high-throughput experiments and simulation. In this work, we propose to apply a Bayesian optimization method to design ultrathin multilayer tungsten-silicon carbide (W-SiC) nanocomposite absorber for high-temperature solar power generation. Based on a semi-analytical scattering matrix method, the design of spectrally selective absorber is optimized over a variety of layer thicknesses to maximize the overall solar absorptance. Our nanofabrication and experimental characterization results demonstrate the capability of the proposed approach for accelerated development of refractory light-absorbing materials. Comparison with other global optimization methods, such as random search, simulated annealing and particle swarm optimization, shows that the Bayesian optimization method can expedite the design of multilayer nanocomposite absorbers and significantly reduce the development cost. This work sheds light on the discovery of novel materials for solar energy and sustainability applications.

Decoupled phononic-electronic transport in multi-phase n-type half-Heusler nanocomposites enabling efficient high temperature power generation

Strongly coupled electronic and thermal transport behavior in thermoelectric (TE) materials has limited their figure of merit (zT). Here we provide breakthrough in decoupling TE parameters in n-type (Hf0.6Zr0.4)NiSn0.99Sb0.01 half-Heusler (hH) alloys through multi-scale nanocomposite architecture comprising of tungsten nanoinclusions. The tungsten nanoparticles not only assist electron injection, thereby improving electrical conductivity, but also enhance the Seebeck coefficient through energy filtering effect. The microstructure comprises of disordered phases with varying size of microstructural features, which assists in effective scattering of heat-carrying phonons over diverse mean-free-path ranges. Cumulatively, these effects are shown to result in outstanding thermoelectric performance of zTmax ∼ 1.4 at 773 K and zTavg ∼ 0.93 between 300 and 973 K. Using this material, a TE generator is demonstrated, which exhibits high power density of 13.93 W cm−2 and conversion efficiency of 10.7% under ΔT = 674 K. The fundamental material design principle for TE nanocomposites demonstrated here can be generalized and extended to other TE systems.

N-Type TaCoSn-Based Half-Heuslers as Promising Thermoelectric Materials.

Half-Heusler compounds are recognized as promising thermoelectric materials for high-temperature power generation, but their relatively high lattice thermal conductivity impedes further improvement of ZT. Here, we report the synthesis of a new half-Heusler compound TaCoSn with a low thermal conductivity. Experimentally, the pristine TaCoSn exhibits a low lattice thermal conductivity of ∼5.7 W m-1 K-1 at 300 K, which is lower than that of most of the other half-Heusler compounds. Phonon calculations by density functional theory indicate that the low phonon velocity, small Debye temperature, and large Grüneisen parameter are the contributors to the low thermal conductivity of TaCoSn. Importantly, intense point-defect scattering can be induced by alloying Nb at the Ta site, which further suppresses the thermal conductivity of TaCoSn. Additionally, Sb has been identified as an efficient dopant for supplying high electron concentration. Finally, the optimized n-type Ta0.6Nb0.4CoSn0.94Sb0.06 demonstrates a peak ZT above 0.7 at 973 K. Our work demonstrates that the TaCoSn-based half-Heuslers are promising thermoelectric materials.

Cellular automata simulation on the corrosion behavior of Ni-base alloy in chloride molten salt

Chloride molten salt is required to study its corrosion behavior since it is recommended to be used as heat transfer and heat storage material in high-temperature thermal power generation system. In this paper, a simplify model was established by the reaction of diffusive corrosive gas and metal substrate in a chloride molten salt. A cellular automaton model based on the stochastic approach is adopted to simulate the uniform corrosion and the migration of metallic element. The corrosion behavior is also simulated considering the practical working condition, such as oxygen, moisture and so on. By comparing the simulation results with experimental data, it proves that the cellular automata simulation is an effective alternative method to describe the high-temperature corrosion process of molten salts. Simulation results of 25,000 time steps is taken as a comparison of the 21-day corrosion which reflects the Cr distribution, and the growth of corrosion layer with the migration of Cr element was reproduced. The change of corrosion layer thickness is similar to the mass loss. The simulation method provides insight on the distribution of corrosion products, corrosion kinetics and morphologies for the long-term application.