Experimental analysis of ammonia–water rectification in absorption systems with the 10 mm metal Pall ring packing

In this paper, the mass transfer performance of the 10 mm metal Pall ring packing for ammonia rectification in ammonia–water absorption refrigeration systems (AARS) is investigated. The experimental setup is described and the experimental procedure and data reduction method are explained. Experimental results of the top vapour temperature, concentration and mass flow rate are presented for different operating conditions, including reflux ratio values from 0.4 to 1 (total reflux conditions). Vapour phase mass transfer coefficients are calculated from the measured data and the results are compared with different mass transfer correlations found in the open literature. In this paper, a correlation is proposed for the packing analysed which was fitted from the experimental data. Finally, a comparison is made between the actual packing height used in the experimental setup and the height required to obtain the same ammonia rectification in AARS with the first generation packings: ½″ ceramic Berl saddles, 15 mm glass Raschig rings and ½″ ceramic Novalox saddles. It was found that a packing height reduction between a factor of 2.5 and 3 is attained with 10 mm metal Pall rings.     

Experimental and numerical research on high‐temperature thermal insulation performance of lightweight porous ceramic/nanomaterial composite structure

The thermal protection structure of hypersonic vehicles must meet the design requirements of high efficiency and light weight, and its heating surface must also be able to withstand thermal erosion by high‐speed and high‐temperature airflow. In this paper, a light‐weight porous ceramic material and a lightweight nanoscale thermal insulation material with excellent thermal insulation performance are combined to form an integrated thermal protection structure. Experimental study and numerical simulation of the structure's high‐temperature thermal insulation performance are carried out. The experimental results show that a composite sheet made from a 20 mm‐thick lightweight porous ceramic material and a 10 mm‐thick nanomaterial exhibit a temperature drop of 85 % between its back surface and front surface in four thermal environments (1200, 1000, 800 and 600 °C) at 1800 s. This indicates excellent thermal insulation performance of the composite sheet. In addition, the operating temperature limit (<1000 °C) is obtained through high‐temperature thermal performance tests on single‐layer nanomaterial sheets and scanning electron microscopy results. This provides an important basis for determining and optimizing the thickness ratio of the two materials in composite structure.     

Solution‐Processed All‐Ceramic Plasmonic Metamaterials for Efficient Solar–Thermal Conversion over 100–727 °C

Low‐cost and large‐area solar–thermal absorbers with superior spectral selectivity and excellent thermal stability are vital for efficient and large‐scale solar–thermal conversion applications, such as space heating, desalination, ice mitigation, photothermal catalysis, and concentrating solar power. Few state‐of‐the‐art selective absorbers are qualified for both low‐ ( < 200  ° C) and high‐temperature ( > 600  ° C) applications due to insufficient spectral selectivity or thermal stability over a wide temperature range. Here, a high‐performance plasmonic metamaterial selective absorber is developed by facile solution‐based processes via assembling an ultrathin ( ≈ 120 nm) titanium nitride (TiN) nanoparticle film on a TiN mirror. Enabled by the synergetic in‐plane plasmon and out‐of‐plane Fabry–Pérot resonances, the all‐ceramic plasmonic metamaterial simultaneously achieves high, full‐spectrum solar absorption (95%), low mid‐IR emission (3% at 100  ° C), and excellent stability over a temperature range of 100–727  ° C, even outperforming most vacuum‐deposited absorbers at their specific operating temperatures. The competitive performance of the solution‐processed absorber is accompanied by a significant cost reduction compared with vacuum‐deposited absorbers. All these merits render it a cost‐effective, universal solution to offering high efficiency (89–93%) for both low‐ and high‐temperature solar–thermal applications.     

Microwave dielectric properties and sintering behavior of nano-scaled (α + θ)-Al2O3 ceramics

The dielectric properties at microwave frequencies and the microstructures of nano (α + θ)-Al₂O₃ ceramics were investigated. Using the high-purity nano (α + θ)-Al₂O₃ powders can effectively increase the value of the quality factor and lower the sintering temperature of the ceramic samples. Grain growth can be limited with θ-phase Al₂O₃ addition and high-density alumina ceramics can be obtained with smaller grain size comparing to pure α-Al₂O₃. Relative density of sintered samples can be as high as 99.49% at 1400 °C for 8 h. The unloaded quality factors Q × f are strongly dependent on the sintering time. Further improvement of the Q × f value can be achieved by extending the sintering time to 8 h. A dielectric constant (_r) of 10, a high Q × f value of 634,000 GHz (measured at 14 GHz) and a temperature coefficient of resonant frequency (τ_f) of −39.88 ppm/°C were obtained for specimen sintered at 1400 °C for 8 h. Sintered ceramic samples were also characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Sintering of Fe-doped Bi0.5Na0.5TiO3 at < 1000 °C

Fe-doped Bi_0.5Na_0.5TiO₃ ceramics with Fe-ion content varied from 0 to 0.15 at.% were successfully prepared by conventional solid state reaction method. The sintering temperature used was between 850 and 1000 °C. X-ray diffraction patterns showed that all produced ceramics were single phase with a rhombohedral structure. SEM micrographs of the ceramics showed a dramatic change in densification behavior as a result of Fe-ion doping. At 850 °C, the undoped BNT ceramic had a very porous structure. As the Fe-ion concentration increased, the ceramics showed denser microstructures and, for the sample containing 0.15 at.% Fe, a very dense grain structure with almost no porosity was obtained. This microstructural observation agreed well with the measured density whose value increased with increasing Fe content. The relative density of at least 95% was achieved in 0.15 at.% Fe-doped BNT ceramics even when it was sintered at 850 °C. Increasing the sintering temperature only had an effect of increasing the grain size of this sample without appreciably affecting its density. The results of this investigation showed that addition of Fe₂O₃ in BNT could help improve the densification process and significantly reduced the sintering temperature of BNT ceramics.     

High performance infra-red detectors based on Si/SiGe multilayers quantum structure

Recently, single crystalline (Sc) Si/SiGe multi quantum structure has been recognized as a new low-cost thermistor material for IR detection. Higher signal-to-noise (SNR) ratio and temperature coefficient of resistance (TCR) than existing thermistor materials have converted it to a candidate for infrared (IR) detection in night vision applications. In this study, the effects of Ge content, C doping and the Ni silicidation of the contacts on the performance of SiGe/Si thermistor material have been investigated. Finally, an uncooled thermistor material with TCR of −4.5%/K for 100 μm × 100 μm pixel sizes and low noise constant (K_1/f) value of 4.4 × 10⁻¹⁵ is presented. The outstanding performance of the devices is due to Ni silicide contacts, smooth interfaces, and high quality multi quantum wells (MQWs) containing high Ge content.     

Study on a 10 W/90 K in-line pulse tube cryocooler

A Stirling-type in-line pulse tube cryocooler (PTC) has been designed, built and tested at Shanghai Institute of Technical Physics (SITP), Chinese Academy of Sciences. This PTC prototype can obtain a low-noise cooling capacity of more than 10 W at around 90 K cold head temperature and is used for cooling a space-borne infrared photo detector. In order to achieve a highly efficient PTC, a simplified numerical simulation model has been established for design and optimization. The simulation results of the regenerator, pulse tube and inertance tube are analyzed in detail. Besides, some key parameters of the PTC are listed in the paper. The PTC’s performances are tested at different operating frequencies from 42 Hz to 55 Hz and its reject temperature dependence is observed in the range of 290 K to 320 K. Furthermore, the map of the PTC’s performance characteristics is presented.     

Manipulating Crystallographic Orientation via Cross-Linkable Ligand for Efficient and Stable Perovskite Solar Cells

The crystallographic orientation of polycrystalline perovskites is found to be strongly correlated with their intrinsic properties; therefore, it can be used to effectively enhance the performance of perovskite-based devices. Here, a facile way of manipulating the facet orientation of polycrystalline perovskite films in a controllable manner is reported. By incorporating a cross-linkable organic ligand into the perovskite precursor solution, the crystal orientation disorder can be reduced in the resultant perovskite films to exhibit the prominent (001) orientation with a preferred stacking mode. Moreover, the as-formed low-dimensional perovskites (LDPs) between the organic ligand and the excess lead iodide can passivate the defects around the grain boundaries. Consequently, highly efficient p-i-n structured perovskite solar cells (PSCs) can be made in both rigid and flexible forms from modified perovskites to show high power conversion efficiencies (PCE) of 24.12% and 23.23%, respectively. The devices also exhibit superior long-term stability in a humid environment (with T₉₀ > 1000 h) and under thermal stress (retaining 87% of its initial PCE after 1000 h). More importantly, the ligand enables the derived LDPs to be crosslinked (under 254 nm UV illumination) to demonstrate excellent mechanical bending durability in flexible devices.     

Solution‐Processed Ti3C2Tx MXene Antennas for Radio‐Frequency Communication

Highly integrated, flexible, and ultrathin wireless communication components are in significant demand due to the explosive growth of portable and wearable electronic devices in the fifth‐generation (5G) network era, but only conventional metals meet the requirements for emerging radio‐frequency (RF) devices so far. Here, it is reported on Ti₃C₂T_x MXene microstrip transmission lines with low‐energy attenuation and patch antennas with high‐power radiation at frequencies from 5.6 to 16.4 GHz. The radiation efficiency of a 5.5 µm thick MXene patch antenna manufactured by spray‐coating from aqueous solution reaches 99% at 16.4 GHz, which is about the same as that of a standard 35 µm thick copper patch antenna at about 15% of its thickness and 7% of the copper weight. MXene outperforms all other materials evaluated for patch antennas to date. Moreover, it is demonstrated that an MXene patch antenna array with integrated feeding circuits on a conformal surface has comparable performance with that of a copper antenna array at 28 GHz, which is a target frequency in practical 5G applications. The versatility of MXene antennas in wide frequency ranges coupled with the flexibility, scalability, and ease of solution processing makes MXene promising for integrated RF components in various flexible electronic devices.     

Synergistic Optimization Enables Large-Area Flexible Organic Solar Cells to Maintain over 98% PCE of the Small-Area Rigid Devices

Slot-die coating is generally regarded as the most effective large-scale methodology for the fabrication of organic solar cells (OSCs). However, the corresponding device performance significantly lags behind spin-coated devices. Herein, the active layer morphology, flexible substrate properties, and the processing temperature are optimized synergistically to obtain high power conversion efficiency (PCE) for both the flexible single cells and the modules. As a result, the 1 cm² flexible devices produce an excellent PCE of 12.16% as compared to 12.37% for the spin-coated small-area (0.04 cm²) rigid devices. Likewise, for modules with an area of 25 cm², an extraordinary PCE of 10.09% is observed. Hence, efficiency losses associated with the upscaling are significantly reduced by the synergistic optimization. Moreover, after 1000 bending cycles at a bending radius of 10 mm, the flexible devices still produce over 99% of their initial PCE, whereas after being stored for over 6000 h in a glove box, the PCE reaches 103% of its initial value, indicating excellent device flexibility as well as superior shelf stability. These results, thus, are a promising confirmation the great potential for upscaling of large-area OSCs in the near future.     

A lightweight low-current 10 K magnet for space-flight ADRs

Future space missions will include detectors and other components cooled to cryogenic temperatures by adiabatic demagnetization refrigerators (ADRs) coupled with mechanical cryocoolers. In such systems the ADRs require lightweight, low-current superconducting magnets. At least one of an ADR’s magnets must operate at the cryocooler’s coldest stage temperature. This temperature should be as high as possible in order to improve operating efficiency and design flexibility. Until now all space-flight compatible magnets have been made with NbTi wire, which has limited their operating temperatures to below about 5 K. We have developed a lightweight (1 Kg) low-current (8 A) Nb₃Sn magnet which produces a 3 T central field at 10 K. We explain the choice of this magnet’s specifications and describe its performance testing.     

Flexible All-Solid-State Direct Methanol Fuel Cells with High Specific Power Density

It is vital to create flexible batteries as power sources to suit the needs of flexible electronic devices because they are widely employed in wearable and portable electronics. The direct methanol fuel cell (DMFC) is a desirable alternative portable energy source since it is a clean, safe, and high energy density cell. The traditional DMFC in mechanical assembly and its unbending property, however, prevent it from being employed in flexible electrical devices. In this study, the flexible membrane electrode assembly (MEA) with superior electrical conductivity and nanoscale TiC-modified carbon cloth (TiC/CC) is used as supporting layer. Additionally, solid methanol fuels used in the manufacturing of flexible all-solid-state DMFC have the advantages of being tiny, light, and having high energy density. Furthermore, the DMFC's placement and bending angle have little effect on its performance, suggesting that DMFC is appropriate for flexible portable energy. The flexible all-solid-state DMFC's power density can reach 14.06 mW cm⁻², and after 50 bends at 60°, its voltage loss can be disregarded. The flexible all-solid DMFC has an energy density that is 777.78 Wh Kg⁻¹ higher than flexible lithium-ion batteries, which is advantageous for the commercialization of flexible electronic products.     

18.6 K single-stage high frequency multi-bypass coaxial pulse tube cryocooler

A single-stage high frequency multi-bypass coaxial pulse tube cryocooler (PTC) has been developed for physical experiments. The performance characteristics are presented. At present, the cooler has reached the lowest temperature of 18.6 K with an electric input power of 268 W, which is the reported lowest temperature for single-stage high frequency PTC. The cooler typically provides 0.2 W at 20.6 K and 0.5 W at 24.1 K with the input power of 260 W at 300 K ambient temperature. The cooperation phase adjustment method of multi-bypass and double-inlet shows its advantages in experiments, they might be the best way to get temperature below 20 K for single-stage high frequency PTC. The temperature stability of the developed PTC is also observed.     

Electrical properties of thick-film NTC thermistor composed of Ni0.8Co0.2Mn2O4 ceramic: Effect of inorganic oxide binder

The thick-film NTC thermistors were prepared by screen printing Ni_0.8Co_0.2Mn₂O₄ ceramic on the alumina. The influence of inorganic oxide binder composition and thickness of thermistor layer on the thermistor constant and initial resistivity are studied. The relation between the resistivity (ρ) and the absolute temperature for the prepared thick-film thermistor comply with Arrhenius equation. The room temperature sheet resistivities of the thick films were in the range 0.56-7.45 MΩ cm and temperature sensitivity index in the range 1492-3335 K. Binder composition dependent agglomeration of microcrystallites is observed in the microstructure of the thick-film Ni_0.8Co_0.2Mn₂O₄ ceramic. The spinel ceramic was prepared by oxalate co-precipitation and sintering.     

Epitaxial La2 / 3Sr1 / 3MnO3 thin films with unconventional magnetic and electric properties near the Curie temperature

We used Pulsed Laser Deposition (PLD) in oxidizing environment to epitaxially grow optimally doped manganite La_2 / 3Sr_1 / 3MnO₃ (LSMO) thin films over a (001) oriented SrTiO₃ substrate. Synthesized samples show good room temperature magnetic properties accompanied by a peculiar extension of the metallic conduction regime to temperatures higher than the Curie point.In this paper we present a study of the dependence of transport and magnetic properties of LSMO thin films on the oxygen pressure during PLD growth. We show how interaction of the growing films with O₂ molecules is fundamental for a correct synthesis and in which way it is possible to adjust PLD experimental parameters in order to tune LSMO thin film properties.The persistence of the metallic conduction regime above the Curie temperature indicates some minor changes of the electronic structure near the Fermi level, which is responsible for the half-metallic behavior of LSMO at low temperature. This feature is rather intriguing from the technological point of view, as it could pave the way to the increase of operating temperature of devices based on LSMO.     

High‐Performance Flexible Photodetectors based on High‐Quality Perovskite Thin Films by a Vapor–Solution Method

Organometal halide perovskites are new light‐harvesting materials for lightweight and flexible optoelectronic devices due to their excellent optoelectronic properties and low‐temperature process capability. However, the preparation of high‐quality perovskite films on flexible substrates has still been a great challenge to date. Here, a novel vapor–solution method is developed to achieve uniform and pinhole‐free organometal halide perovskite films on flexible indium tin oxide/poly(ethylene terephthalate) substrates. Based on the as‐prepared high‐quality perovskite thin films, high‐performance flexible photodetectors (PDs) are constructed, which display a nR value of 81 A W^?1 at a low working voltage of 1 V, three orders higher than that of previously reported flexible perovskite thin‐film PDs. In addition, these flexible PDs exhibit excellent flexural stability and durability under various bending situations with their optoelectronic performance well retained. This breakthrough on the growth of high‐quality perovskite thin films opens up a new avenue to develop high‐performance flexible optoelectronic devices.     

Ca<Subscript>3</Subscript>WO<Subscript>6</Subscript>: a novel microwave dielectric ceramic with complex perovskite structure

Present work introduces a novel Ca₃WO₆ microwave dielectric ceramic with a complex perovskite structure. The Ca₃WO₆ ceramic was prepared by solid state reaction method and can be well densified at above 1,260 °C for 2 h in air. All the XRD patterns can be fully indexed as a single-phase monoclinic structure (space group P2₁/n). The sharp Raman vibration mode at 810 cm⁻¹ suggests the long range order in the Ca₃WO₆ structure. The best microwave dielectric properties can be obtained in ceramic sample sintered at 1,275 °C for 2 h with a permittivity ~15.3, a Qf value ~29,200 GHz and a TCF value about −30 ppm/°C. Applying the oxide additivity rule, the calculated permittivity agrees well with the measured value. This kind of ceramic might have some potential value for microwave application for its good microwave dielectric behavior. The (Ca_1/2W_1/2) complex cations holding the site of Ti⁴⁺ in perovskite structure would introduce many new systems in complex perovskite compounds in the future.     

Impedance analysis of MnCoCuO NTC ceramic

Impedance spectroscopy is often used to analyse the electrical properties of ceramic materials having high-resistive grain boundaries, such as ZnO and SrTiO₃. Fewer attempts have been made at using this technique for the analysis of inhomogeneous electronic ceramics consisting of grains with differing composition, such as those occurring in negative temperature coefficient (NTC) thermistors. In this study, we have attempted to adopt ac impedance spectroscopy together with other techniques to analyse an NTC thermistor ceramic material.An Mn, Co and Cu multielements transition metal oxide (MnCoCuO) ceramic was prepared by using homogeneous precipitation employing oxalic acid. This material displayed a typical NTC effect, showing an electrical resistance decrease with temperature when dc electrical measurement was performed. The ac impedance spectroscopy analysis showed that there were two peaks in impedance and conductance versus frequency plot. By using an alternative representation of impedance spectra Z″/f versus Z′, three distinct relaxation frequency ranges were identified. They are believed to originate, respectively, from the electrode, phase 1 (rich-Cu phase) and phase 2 (poor-Cu phase) grains existing in this ceramic. SEM observation and EDX analysis clearly showed existence of two distinct phase grains. The resistance values were derived from phases 1 and 2 grains based on ac impedance data. The sum of the resistance values was in good agreement with that from dc measurement in the temperature range of 30-95 °C. The material constant, B, for the two phases was also calculated, giving 3100 and 3600 K for phases 1 and 2, respectively.     

Design and experimental investigation of the high efficiency 1.5 W/4.2 K pneumatic-drive G-M cryocooler

The development of a high cooling power and high efficiency 4.2 K two stage G-M cryocooler is critically important given its broad applications in low temperature superconductors, MRI, infrared detector and cryogenic electronics. A high efficiency 1.5 W/4.2 K pneumatic-drive G-M cryocooler has recently been designed and developed by ARS. The effect of expansion volume rate and operation conditions on the cooling performance has been experimentally investigated. A typical cooling performance of 1.5 W/4.2 K has been achieved, and the minimum temperature of the second stage is 2.46 K. The steady input power of the compressor at 60 Hz is 6.8 kW, while the operation speed of the rotary valve is 30 rpm. A maximum cooling power of 1.75 W/4.2 K has been obtained in test runs.     

Status and strategies for fabricating flexible oxide ceramic micro-nanofiber materials

Oxide ceramic microfibers with low thermal conductivity, high temperature, and corrosion resistance have been widely used in the field of thermal insulation. When the fiber diameter is reduced to the nanoscale (<1000 nm), the high specific surface area and porosity brought by the diameter refinement endow these nanofibers with unique thermal, optical, electrical and other properties, which are expected to be applied in advanced high-tech fields. Oxide ceramic micro-nanofibers (MNFs) belong to a new structural ceramic system, but they suffer from intrinsic hardness and brittleness. We have been committed to developing new textile technologies and fabricating flexible oxide ceramic MNFs. In this review, the development status of oxide ceramic MNFs and their applications are first briefly summarized. Then, the definition of flexibility and flexibility mechanisms of MNFs, as well as the strategies and methods for fabricating flexible oxide ceramic MNFs are comprehensively discussed. Finally, our perspective on the future development of oxide ceramic MNFs is proposed. We suppose that they will develop toward the direction of flexibility, porosity, multifunctionality, thin film, and aerogels, and their functional applications will permeate from the traditional heat insulation to the emerging fields such as flexible electronics and batteries, intelligent artificial muscle, and industrial catalysis.