High Thermal Cycling Research Articles

Effect of High Temperature and Thermal Cycle of 4043 Al Alloy Manufactured through Continuous Casting Direct Rolling.

CCDR 4043 Al alloys are an outstanding candidate for producing mechanical components for automotive or aircraft engines. Two experimental environments-sustained high temperature and repeated heating-cooling-were simulated in the laboratory to replicate the actual operating conditions of engine components. This research investigated the microstructural evolution, mechanical properties, and fracture characteristics of the 4043 Al alloy manufactured through the continuous casting direct rolling (CCDR) process under different post-processing conditions. The CCDR process combines continuous casting, billet heating, and subsequent continuous rolling in a single equipment of production line, enabling the mass production of Al alloy in a cost-effective and energy-efficient manner. In the present work, the 4043 alloy was subjected to two environmental conditions: a sustained high-temperature environment (control group) and a cyclic heating-cooling environment (experimental group). The maximum temperature was set to 200 °C in the experiment. The experimental results show that, in a sustained high temperature working environment, the strength and elongation of the CCDR 4043 Al alloy tend to be stable. The overall effect involves the Al matrix softening and the spheroidization of eutectic Si caused by prolonged exposure to high temperature. This can enhance its ductility while retaining a certain level of mechanical strength. Comparatively, in the working environment of cyclic heating-cooling (thermal cycle), the direction of Si diffusion was different in each cycle, thus leading to the formation of an irregular Ai-Si eutectic structure containing precipitated Si particles of different sizes. The two compositions of Al and Si with very different thermal expansion coefficients may induce defects at the sharp points of Si particles under repeated heating-cooling, thereby reducing the strength and ductility of the material. The results of this work can confirm that the fracture behavior of 4043 Al alloys is obviously controlled by the morphology of the precipitated eutectic Si. In addition, CCDR 4043 Al alloys are not suitable to be used in working environments with a thermal cycle. In practical applications, it is necessary to add traces of special elements or to employ other methods to achieve the purpose of spheroidizing the precipitated eutectic Si and Al-Fe-Si phases to avoid the deterioration of strength and ductility under cyclic heating. To date, no other literature has explored the changes in the microstructure and mechanical properties of CCDR 4043 Al alloys across various time scales under the aforementioned working environments. In summary, the findings provide valuable insights into the effect of thermal conditions on the properties and behavior of CCDR 4043 Al alloys, offering potential applications for it in various engineering fields, such as the automotive and aerospace industries.

Preparation and thermophysical properties of a novel metallic microencapsulated phase change material/eutectic salt/ceramic composite

The development of thermal storage material is crucial for the utilization of thermal energy. At present, eutectic salt/ceramic composite has been widely studied as latent heat storage material, however, its thermal conductivity is low and its latent heat per unit volume is still not ideal, despite its high latent heat per unit mass. Herein, a metallic microcapsule with high thermal conductivity and latent heat per unit volume is introduced to improve the above properties. Using MgO as the support material, metallic microcapsule (Sn@Void@SiO2) and eutectic salt (LiNO3-NaCl) with almost the same temperature range as phase change material, metallic microcapsule/eutectic salt/ceramic composite was prepared by cold-pressure sintering method. The result shows that the best performance of metallic microcapsule/eutectic salt/ceramic composite was achieved with the addition of 30 wt% Sn@Void@SiO2 instead of MgO, the latent heat per unit volume and per unit mass of the composite are 237.1 J/cm3 and 117.9 J/g, which are improved by 56.72 % and 15.48 % respectively. And the thermal conductivity of the composite was improved by 63.79 %, from 0.58 W/(m·K) to 0.95 W/(m·K). Further, the addition of a small amount of Sn to metallic microcapsule/eutectic salt/ceramic composite can not only increase its latent heat but also improve its thermal conductivity as Sn fills the pores inside the composite after melting. The result showed that the thermal conductivity of the composite was increased by 155.17 % than that of eutectic salt/ceramic composite when Sn was added at 5 wt%. Finally, thermal cycle results showed that composites have high thermal reliability and proved high thermal cycling stability of metallic microcapsule prepared by “double-layer coating, sacrificial inner layer” method.

Taguchi Optimization of Electrolytic Plasma Hardening Process Parameters on Ti‐6Al‐4V Alloy: Microstructure and Mechanical Properties

Herein, the effects of electrolytic plasma treatment (EPT) on the hardness distribution, wear resistance, and surface morphologies of titanium alloy (Ti‐6Al‐4V) at three different thermal cycles (4‐5‐6 times) are investigated. The microstructure is controlled by heat temperature and modification times of thermal cycles depending on EPT processing parameters. A novel technique to modify Ti‐6Al‐4V alloy by the process of EPT successfully occurs. The results show that the phase transformation is shown as follows: fine α and β for the low thermal cycle → irregular martensite α′ for the high thermal cycle → complete zigzag martensite α′ for the max thermal cycle. The hardness is increased from 350 ± 10HV0.05 to 530 ± 10HV0.05 after the modification. Wear tests are conducted according to the Taguchi L9 (3^3) orthogonal array. Three parameters (load, sliding speed, and sample type) with three levels examine wear rate and coefficient of friction. Optimum levels are obtained by Taguchi analysis from the experimental results. In addition, an analysis of variance is performed to find the effectiveness of the parameters. The wear surfaces are analyzed by scanning electron microscope. After the analysis, the best result is obtained in five thermal cycles.

Composite phase change materials based on CuS-coated carbonized melamine foam/reduced graphene oxide frameworks for multiple energy conversion and storage applications

The single function and leakage of organic phase change materials (OPCMs) used alone considerably limit the scope of their large-scale applications. An efficient method of addressing this issue is by adding functional fillers and porous scaffolds to OPCMs. In this study, a novel CuS-coated carbonized melamine foam (CMF)/reduced graphene oxide (rGO) framework (CMF/rGO/CuS) was developed for the preparation of stable multifunctional OPCMs. The functional materials rGO and CuS were used as reinforcing materials, and CMF was used as a supporting material. Paraffin wax (PW), a thermal storage substance, was encapsulated in the CMF/rGO/CuS framework by vacuum-assisted impregnation to obtain a PW@CMF/rGO/CuS composite with excellent comprehensive properties. When the concentration of the conductive filler CuS was 2.0 wt%, the conductivity of the PW@CMF/rGO/CuS 2.0was 73.7 % more than that of pure PW, and its photothermal conversion efficiency exceeded 90 %. Meanwhile, CMF/rGO/CuS endowed the composite with a thermal conductivity of 0.2525 W m−1 K−1, which was 33.6 % higher than that of pure PW. Finally, PW@CMF/rGO/CuS demonstrated high thermal cycling and thermal cycling stability with good application prospects in various fields.

Flexible core–shell structured Al-Cu alloy phase change materials for heat management

The development of core–shell structured phase change materials (PCMs) with tunable melting points has been attracted much attention for thermal storage of solar energy, and a flexible shell is crucial for their practical applications. Herein, we prepared microencapsulated Al-Cu alloy PCMs (MEPCMs) with a flexible shell by a deposition-oxidizing calcination method. The Cu nanoparticles are chemically deposited on the surface of Al powders by a rapid replacement reaction, which further promotes the formation of Al-Cu alloy microspheres and the oxidation of Al to form Al2O3 shell during oxidation calcination. The prepared MEPCMs show excellent thermal cyclic performance and tunable melting point (549–592 °C). The presence of a thin film between the Al2O3 shell and Al-Cu alloy core may act as a buffer to accommodate volume change during melting-freezing process, obtaining a flexible core–shell structure. The heat storage density of Al-Cu alloy MEPCMs decreases by only 0.09% after 100 melting-freezing cycles, indicating high thermal cycling stability. In addition, the microencapsulated Al-Cu alloys present high latent heat (208.6–222.3 J·g−1) and relatively high thermal conductivity (∼1.8 W·(m·K)−1), which makes it attractive for application in high-temperature thermal storage systems.

An Efficient Procedure for Bonding Piezoelectric Transducers to Thermoplastic Composite Structures for SHM Application and Its Durability in Aeronautical Environmental Conditions

Piezoceramic transducers (PCTs) bonded to carbon fiber-reinforced plastic (CFRP) composite structures must be durable as well as remain properly bonded to the structure in order to provide reliable data for accurate guided-wave-based structural health monitoring (SHM) of aeronautical components. The current method of bonding transducers to composite structures through epoxy adhesives faces some shortcomings, such as difficult reparability, lack of weldability, longer curing cycles, and shorter shelf life. To overcome these shortcomings, a new efficient procedure for bonding the transducers to thermoplastic (TP) composite structures was developed by utilizing TP adhesive films. Application-suitable TP films (TPFs) were identified and characterized through standard differential scanning calorimetry (DSC) and single lap shear (SLS) tests to study their melting behavior and bonding strength, respectively. Special PCTs called acousto-ultrasonic composite transducers (AUCTs) were bonded to high-performance TP composites (carbon fiber Poly-Ether-Ether-Ketone) coupons with a reference adhesive (Loctite EA 9695) and the selected TPFs. The integrity and durability of the bonded AUCTs in aeronautical operational environmental conditions (AOEC) were assessed in accordance to the standard Radio Technical Commission for Aeronautics DO-160. The AOEC tests performed were operating low and high temperatures, thermal cycling, hot-wet, and fluid susceptibility tests. The health and bonding quality of the AUCTs were evaluated by the electro-mechanical impedance (EMI) spectroscopy method and ultrasonic inspections. The AUCT defects were created artificially and their influence on the susceptance spectra (SS) was measured to compare them with the AOEC-tested AUCTs. The results show that a small change occurred in the SS characteristics of the bonded AUCTs in all of the adhesive cases after the AOEC tests. After comparing the changes in SS characteristics of simulated defects with that of the AOEC-tested AUCTs, the change is relatively smaller and therefore it can be concluded that no serious degradation of the AUCT or the adhesive layer has occurred. It was observed that the most critical tests among the AOEC tests are the fluid susceptibility tests, which can cause the biggest change in the SS characteristics. Comparing the performance of the AUCTs bonded with the reference adhesive and the selected TPFs in the AOEC tests, it was seen that some of the TPFs, e.g., Pontacol 22.100 outperforms the reference adhesive, while the other TPFs have similar performance to that of the reference adhesive. Therefore, in conclusion, the AUCTs bonded with the selected TPFs can withstand the operational and environmental conditions of an aircraft structure, and hence, the proposed procedure is easily installed, reparable, and a more reliable method of bonding sensors to aircraft structures.

Fracture mechanics of polymer concretes: A review

One of the main advantages of polymer concrete (PC) composites compared to ordinary cement concretes is having much higher fracture toughness and fracture energy. In this review, after a brief introduction to fracture mechanics, the standard test methods to determine the fracture properties of PC are considered. Different types of specimens used in fracture tests, the governing equations, and their fracture patterns are evaluated. Afterward, the parameters affecting the fracture properties of PC including materials (resins, aggregates, fibers, and nanofillers), and the specimen parameters (shape and size, crack depth, and crack angle) are investigated. Like the other mechanical properties, exposure to high temperatures, thermal cycles, and chemical solutions as well as exposure to the atmospheric condition can have destructive effects on the fracture properties of the PC, which are reviewed based on the results of the previous studies. These findings provide a necessary comprehensive understanding of the fracture mechanics of polymer concretes. After reviewing and summarizing almost all the research conducted in this field, research gaps are pointed out and suggestions for future works are presented.

Effects of different physical properties of anthracite powder fuel on detonation characteristics of a rotating detonation engine

The rotating detonation engine (RDE) fueled by coal powder has attracted much attention because of its high thermal cycle efficiency. To explore the detonation characteristics of anthracite powder and further study the effects of particle size and morphology on them, a series of rotating detonation experiments with anthracite powder were carried out in a disk-shaped combustor. The experimental results show that the morphology of anthracite particles plays an important role in detonation. The addition of porous anthracite (PA) enhances the detonation intensity in the lean hydrogen–air, while flaky anthracite (FA) weakens it. The concentration rise of PA increases the detonation wave height, while FA does not have such an obvious effect on the height. The excessive addition of any anthracite powder increases the heat loss of the detonation, resulting in a decrease in detonation velocity. By comparing the detonation characteristics of 20-nm, 3-μm, and 40-μm PA, it is found that the detonation performance of 20-nm PA, which has strong agglomeration, has no significant advantages over the micron-sized PA. Among the three PA powders, 3-μm PA has the largest detonation intensity and velocity. The difference in engine performance caused by pulverized anthracite with different morphological characteristics is as follows: when the mass flow rates of coal, H2, and air are 6.7, 5.3, and 260 g/s, respectively, the specific impulse of 3-μm PA reaches 7.8 kN·s/kg, which is about 2.7 times higher than that of 5-μm FA. This research provides theoretical guidance for the powder fuel selection of the RDE.

Evaluation of epoxy-based coating degradation under thermal insulation at elevated temperatures on different steel substrates

Corrosion under insulation (CUI) remains one of the most critical issues in the petrochemical industry. In a typical CUI system, protective coatings (organic or metallic) are used primarily as the last barrier to prevent the rapid corrosion of the metallic substrate. However, organic coatings exposed to high operating temperatures and thermal cycling conditions are susceptible to failure and thus require coating performance evaluations under representative thermal insulation conditions. This study presents experimental designs to investigate the degradation of an organic polyamine-cured epoxy coating under accelerated laboratory test conditions. Additionally, a systematic CUI evaluation protocol for high-temperature organic coating performance is presented. The method involved specially designed apparatus to simulate CUI systems and characterisation techniques, such as visual inspection, adhesion test, peel-off test, scanning electron microscopy, electrochemical impedance spectroscopy, and chemical analysis using Fourier-transform infrared spectroscopy, and differential scanning calorimetry. The results showed that polyamine-based epoxy coating experienced thermal degradation starting at temperatures above 130 °C under mineral wool insulation in accelerated and cyclic CUI tests. Chemical degradation was the primary mode of degradation, with the formation of carbonyl functional groups and increased glass transition temperature observed at higher exposure temperatures. The proposed combination of electrochemical, spectroscopic, mechanical, and microscopy techniques allows quantifying coating performance under insulation and subsequently provides insights into predicting coatings' service lifetime.

Surface integrity of Ti-6Al-4V alloy in hybrid electrical discharge machining processes

Titanium alloy is one of the difficult-to-machine materials. The final conditions of the machined surface of this alloy are influenced by electro-discharge machining. High temperatures and thermal cycles in machining operation induce undesirable alterations in the surface quality of Ti-6Al-4V. One of the ways to improve the negative effects of electrical discharge machining is to use hybrid methods. There is no comprehensive research on the effect of hybrid electrical discharge machining process on the surface integrity of the Ti-6Al-4V alloy. In this paper, hybrid electrical discharge machining techniques including ultrasonic-assisted electrical discharge machining, powder-mixed dielectric electrical discharge machining using Al2O3 nanopowders and powder-mixed dielectric combined with ultrasonic-assisted electrical discharge machining, were used for processing of this alloy. The hybrid electrical discharge machining processes were evaluated by basic specifications of surface integrity including surface cracks, heat affected area, residual stress, and corrosion resistance. It was found that in powder-mixed dielectric combined with ultrasonic-assisted electrical discharge machining process, developed microcracks were very low and this process developed a thinner heat-altered layer, compared to traditional electrical discharge machining process, which produced a thicker heat-altered layer. The findings also, demonstrated that ultrasonic waves have reduced residual stresses compared to other methods and its stress diagram was distinct in comparison with the other processes. The corrosion rate of samples machined by electrical discharge machining process was higher than other hybrid processes; in powder-mixed dielectric electrical discharge machining process, the machined samples had the highest corrosion resistance.

The preparation of anisotropic conductive paste and its application in FOB interconnection

PurposeThe purpose of this study is to investigate the reliability of flex-on-board (FOB) interconnection connected with an anisotropic conductive paste (ACP), which is prepared by dispersing nickel balls in the epoxy-curing system.Design/methodology/approachDifferential scanning calorimetry was used to evaluate the curing characteristics of the paste. And the contact resistances of bonding joints and 90º peel adhesion were tested before and after high temperature and high humidity test (85°C, 85% humidity), thermal cycling (−45°C∼125°C, 30min/cycle) and pressure cooker test (PCT, 121°C, 100% humidity 2 atm) to evaluate the flex on board (FOB) interconnection reliability.FindingsIt is found that FOB test vehicles have been successfully bonded by using ACP for the first time. And the ACP bonding joint of FOB has good reliability and can meet the requirements of FOB interconnection. Compared with conventional anisotropic conductive film (ACF), this ACP interconnection provides higher adhesion strength, higher joint current carrying capability and higher reliability performance and lower cost for FOB interconnection.Originality/valueACP is applied in the interconnection of FOB. It has the higher reliability performance and lower cost for than the conventional ACF.

Directional fiber framework wrapped by graphene flakes for supporting phase change material with fast thermal energy storage properties

Organic phase change materials (PCMs) have low thermal conductivity and poor form stability, which prohibit their usage in high-efficient heat storage and thermal management. This study demonstrated how to efficiently fabricate phase change composites (PCCs) with directional thermal conductivity and good form stability using vertically aligned carbon fibers as supporting scaffolds. Cotton blankets with aligned fibers were firstly impregnated with graphene flake solutions, which were then rolled to columns along the fiber direction and subsequently carbonized to obtain the porous carbon fiber scaffolds. PCCs were prepared by vacuum impregnation of paraffin into the scaffolds. The porous scaffolds supported PCCs showed good shape stability and greatly improved thermal transfer properties, which were especially endowed with a directional heat conductivity as a result of the vertically arranged hollow carbon fiber structure. The thermal conductivity of PCCs along the axial direction of the fibers was greater than along the lateral direction, because the arranged fibers provided the majority of the thermal transfer path in PCCs. With a carbon content of 19.46 wt%, the axial thermal conductivity was 2.13 W K−1 m−1, which was twice of the lateral one and 8.5 times of the PW. Last but not least, the PCCs also possessed high latent heat capacity, high thermal cycling and chemical stability. These results suggest that the novel carbon scaffolds may enable PCCs with directionally improved thermal transfer properties.

Shape-Stabilized Phase Change Materials of Stearic Acid Confined in Fumed Silica

Stearic acid (C18OOH) as a phase change material (PCM) possesses high potential for thermal energy storage applications. To prevent leakage of C18OOH in liquid state, a porous support is required to form shape-stabilized PCMs (SSPCMs) by impregnating C18OOH into the porous support. The SSPCMs were carefully investigated to demonstrate how the nanoconfinement in the porous support affects their thermal performance. In this work, a series of stearic acid/fumed silica (C18OOH/FS) SSPCMs with various C18OOH contents was fabricated, and their thermal characteristics were extensively examined. The FS provided an adequate inner void to confine up to 70 wt % C18OOH owing to its high porosity (88%). Meanwhile, C18OOH was well confined within the FS pore structure owing to hydrogen-bonding (H-bonding) interactions, surface tension, and capillary force. The SSPCM with an optimal content of 70 wt % C18OOH exhibited the melting and crystallization temperatures of 66.0 and 63.1 °C, respectively, which are slightly lower than those of pure C18OOH owing to the confinement effects. It also possessed good leakage resistance, a high crystallization fraction of 93.1%, and high thermal energy storage (TES) capacity of 146.3 J/g. Additionally, the composite exhibited excellent thermal cycling stability after 1000 melting/crystallization cycles. The thermal conductivity of the 70 wt % C18OOH/FS SSPCM (0.150 W/m·K) was lower than that of pure C18OOH (0.224 W/m·K), indicating that the SSPCM retards heat transfer during the heat charging and discharging processes. Generally, C18OOH/FS SSPCMs exhibit excellent TES capacity, high thermal cycling stability, and heat transfer retardation properties, with a facile preparation process at a low cost. Therefore, they are ready for industrial-scale applications in the fields of thermal insulation and thermal protection.

Improvement of Shear Strength of Zeolite-Bentonite Liner Material under High Temperatures with Tincal and Pumice

Thermal changes (high temperature and thermal cycles) occur around energy structures, such as energy piles, nuclear waste repositories, etc. Sometimes these temperature changes affect the engineering properties of surrounding soils undesirably. Hence, there is a need for durable soils that can maintain their engineering properties unchanged under high temperature and thermal cycles for a long time. Tincal and pumice are used in the production of temperature-resistant and heat-insulated materials. Therefore, in the present study, 10% and 20% tincal and pumice additives were added to zeolite-bentonite mixtures and shear strength behavior of the mixtures was investigated under room and high temperatures (80°C). According to the results, the maximum shear stress values of zeolite- bentonite mixtures generally increased in the presence of tincal and pumice additives under high temperature. Both additives are effective for improvement, however; the effect of pumice can be more pronounced.

Critical components in supercritical CO2 Brayton cycle power blocks for solar power systems: Degradation mechanisms and failure consequences

This review presents an overview of the critical components in supercritical CO2 Brayton cycle power block systems along with their degradation mechanisms and possible consequences in Concentrated Solar Power (CSP) systems. Requirements for high strength, efficiency, and environmental compatibility are also discussed. sCO2 turbines are advantageous because of their small size and significantly reduced number of turbomachinery components. These components are exposed to a sCO2 environment with high pressures, temperatures, and thermal cycling that can result in premature failure due to fatigue, creep, corrosion, stress corrosion cracking, erosion, and carburization. Nickel and stainless steel candidate alloys have been proposed for sCO2 service and at these operational conditions their failures are discussed. The consequences of loss of containment for typical system designs are also explored with specific reference to potential exothermic reactions with other heat transfer media such as sodium.

Effective thermal conductivity and thermal cycling stability of solid particles for sCO2 CSP applications

A supercritical CO2 (sCO2) Brayton cycle solar power system based on solid particle thermal energy storage is proposed to enhance the efficiency of concentrated solar power (CSP). The effective thermal conductivity and thermal cycling stability of solid particles are crucial for sCO2 CSP applications. Some natural and artificial solid particles, such as black silicon carbide, green silicon carbide, white corundum, brown corundum, brown ceramsite sand, garnet, river sand and desert sand are considered as potential thermal energy storage medium due to its low cost and easy availability in large quantities. However, there are few studies about the effective thermal conductivity and stability of these solid particles after thermal cycling tests. In this study, the effective thermal conductivity of these solid particles was measured by the hot wire method. Particularly, the effective thermal conductivity of black silicon carbide and green silicon carbide was measured by modified hot wire method. In addition, the changes of mass, real density, bulk density, void fraction and mean diameter of the above-mentioned solid particles after 100 times thermal cycling tests were also recorded to analyze thermal cycling stability. Based on the results of all the above tests, green silicon carbide exhibits high effective thermal conductivity and good thermal cycling stability, which presents a great potential as a thermal energy storage medium.

Effect of Nb on inclusions and phase transformation in simulated high heat input coarse-grain HAZ of Nb/Ti low carbon microalloyed steel

In this paper, two groups of Nb/Ti low carbon microalloyed steels (Nb-bearing and Nb-free) were obtained through laboratorial methods. The evolution and effect of Nb/Ti-containing complex inclusions were characterised and analysed after being subjected to high heat input thermal simulation of 100 kJ/cm. The results showed that the prior austenite grain size in the coarse grain heat-affected zone (CGHAZ) was not affected by 0.045 wt% Nb addition. However, the acicular ferrite nucleation, induced by effective micron-level inclusions, was inhibited. Nb tended to converge towards the interfaces between the micron-level inclusions and matrix, which had a negative effect on the nucleation potential of acicular ferrite. The re-precipitation behaviour of nano-level inclusions satisfied the dynamic conditions during the high heat input thermal cycle, under which the dislocation movement was inhibited due to the pinning effect of re-precipitation particles. Besides, the size, morphology and composition of nano-level precipitates were changed by Nb (0.045 wt%) addition. In general, the evolution and effect of inclusions in simulated high heat input CGHAZ provide theoretical references for the study of welding performance in Nb/Ti low carbon microalloyed steels. • Nb segregation at the interface between micron inclusion and matrix affects the nucleation of acicular ferrite. • The acicular ferrite nucleation induced by effective inclusions is inhibited by a certain amount of Nb. • The size, morphology and even composition of the nano-level inclusions in CGHAZ are changed by 0.045wt%Nb addition.

Current-Carrying Capability and Magnetic Behavior of the HTS Twisted Stacked-Tape Conductor Cable for the Compact Fusion Reactor

The concept of the high temperature superconducting (HTS) twisted stacked tape conductor (TSTC) cable for fusion has been developed during recent years. The cable is demonstrated to have a stable cable critical current under extreme trial conditions with high electromagnetic force levels and multiple cryogenic thermal cycles. The remaining question is how to enhance the current-carrying capability and magnetic properties of the cable. In this article, three specific TSTC cables with the same twist pitch have been designed. Numerical studies of current-carrying capability and magnetic behavior of these cables have been carried out by employing a T-A formulation model and a H-homogenized formulation model which are based on the finite element method. The two models consider the variation of the critical current density with perpendicular and parallel magnetic fields, and temperature influence on the critical current density has been considered as well. these models have been validated with experiment data and a good fitting curve was obtained. Results show that the 4-slot TSTC cable has a better magnetic behavior compared to the 3-slot and 5-slot TSTC cables, in spite of a better current-carrying capability of the 5-slot cable. The study is of great significance for the research and development of the TSTC cables for compact fusion reactors.

Polyimide/phosphorene hybrid aerogel-based composite phase change materials for high-efficient solar energy capture and photothermal conversion

• We developed a new type of composite PCM for high-efficient solar energy capture. • The composite PCM was based on polyimide/phosphorene hybrid aerogel and PEG . • The introduction of phosphorene enhances solar photothermal absorption and conversion. • The composite PCM presents high solar light-to-heat conversion efficiency. • The composite PCM exhibits great potential for efficient utilization of solar energy. Solar energy is the cleanest and most abundant renewable energy source that can be utilized to displace fossil fuels and provide an effective solution for future energy shortage and climate change. Aiming at enhancing the capture efficiency of solar photothermal energy, we developed a novel type of phase-change composites based on polyimide (PI)/phosphorene (PR) hybrid aerogel and polyethylene glycol (PEG). The composites were prepared by fabricating a series of PI/PR hybrid aerogels with different loadings of PR nanosheets using freeze-drying and thermal imidization techniques, followed by vacuum impregnation of PEG as a phase change material into the aerogel framework. The obtained hybrid aerogels exhibited a lightweight nature with a density of 21.9 mg·cm −3 when 16 wt% PR nanosheets were incorporated, resulting in an extremely high PEG loading of 4067% in the aerogel system. The combination of PI and PR nanosheets leads to a significant enhancement in solar light absorption and photothermal energy conversion for the hybrid aerogel/PEG composites. The loading amount of PEG was also improved remarkably due to an increase in the volume capacity of the hybrid aerogels resulting from the introduction of PR nanosheets. The resultant hybrid aerogel/PEG composites not only exhibit a high latent-heat capacity of over 170 J·g −1 and a high photothermal conversion efficiency of 82.5%, but also show good thermal impact resistance to keep their original shape and form well after heating at 80 °C for 20 min and maintain a high thermal cycle stability after thermally cycled for 500 times. These superior performances make the hybrid aerogel/PEG composites capable of dealing with a wide range of applications in solar photothermal energy capture and storage. This study provides a promising strategy for the design and development of high-performance and lightweight composite PCMs to meet the requirement of applications for efficient utilization of solar energy.

Design and fabrication of aluminum honeycomb sandwich structures by atmosphere protect brazing: Microstructural evolution and mechanical behavior

Aluminum honeycomb sandwich structures with robust interfacial bonding and great mechanical response were fabricated by atmosphere protect brazing technique. The key brazing parameters (brazing temperature, holding time) were investigated and the correlations between interfacial microstructure evolution and mechanical behavior were addressed. Suitable brazing parameters (600 °C-15 min) could not only minimize the deterioration of high thermal cycle on the performance of joints including grain coarsening and over-burning of core walls, but also provide excellent interface metallurgical bonding. Additionally, the dominant failure mode of brazed aluminum honeycomb sandwich structures was core buckling rather than skin-core debonding. This study provides a reliable and efficient method to enhance interfacial bonding and overall performance of honeycomb sandwich structures.