Simulation and risk assessment of hydrogen leakage in hydrogen production container

In this paper, the hydrogen leakage and diffusion characteristics analysis and risk assessment are carried out on the container where a 2 Nm³/h alkaline hydrogen production device is located. Firstly, the transient and steady process of hydrogen leakage from hydrogen production container is analyzed. Secondly, the dynamic balance of combustible hydrogen cloud is analyzed, the concept of critical ventilation flow is put forward. It was found that in order to reduce the flammable volume by 85%, the installed ventilation can only cover the leakage flow of 1.0 Nm³/min. Finally, TNT equivalent method is used to evaluate the hazard degree of hydrogen leakage. It is found that the existed hydrogen production container ventilation device can only exhaust the hydrogen-air cloud with small flow leakage, while the accumulation of gas cloud still exists in large flow leakage. Under the critical ventilation flow, the minor injury radius can be reduced from 4.8 m to 2.78 m. The effect of critical ventilation flow was verified.     

(Ba,Ca)(Ti,Zr)O3–CeO2 translucent and opaque ceramics — Optical and electromechanical characteristics

This work demonstrates promising approaches to synthesize multifunctional-translucent BCZT-CeO₂ ceramic for electro-mechanical/optical conversion. Nearly fully dense BCZT-CeO₂ electroceramics were fabricated by spark plasma sintering (SPS) showing high dielectric permittivity of 5875 and low dielectric loss of 2.1%. Altogether, an extraordinary optical transmittance was attained as ～ 40% at 750 nm wavelength and ～ 46% in the infrared region. The fine grains restricted piezoelectric constant, d₃₃, to a moderate value of ～ 145 pC/N but with an enhanced Curie temperature, T_C ～ 135 °C. Post rapid pressure-less sintering on SPSed samples led to a fast grain growth within an extra hour of sintering and a major improvement of piezoelectric properties (d₃₃ = 532 pC/N and k_p = 43%) was achieved. A substantial amount of energy can be saved by both approaches owing to rapid heating/cooling rates and short dwell-times, at least when compared to conventional sintering. This success highlights ingenious avenues for further studies on BCZT-CeO₂ electro-optical ceramics.     

Developing an advanced ANN-based approach to estimate compaction characteristics of highway subgrade

The current methodology of assessing the compaction characteristic of subgrade fillers is time-consuming. The spot-sampling method and the following laboratory tests bring bias to engineering practice. This study proposes an advanced approach to determine the maximum dry density, optimum moisture content, and compactness of subgrade based on ANN algorithms. A large number of compaction tests are performed to assess the compaction quality of various types of subgrade fillers. The particle gradation is specifically considered. Wave propagations of the compacted specimen are assessed based on the ultrasonic test, and the anisotropic feature is demonstrated. The dynamic elastic parameters are derived to further reveal the interaction mechanism. A dataset is proposed by combining these laboratory data and the literature data. The PSO-BP-NN model is developed to automatically predict the compaction parameters of different filling materials. A positive correlation is demonstrated between the elastic modulus and the total density, and Poisson’s ratio illustrates an inverse trend. The compaction energy is influential to the maximum dry density while the moisture content has the greatest impact on the compactness. This study aims to develop an accurate model to replace the extensive Proctor test and efficiently evaluate the compaction quality of subgrade for highway constructions.     

Photoacoustic dual-gas sensor for simultaneous detection of hydrogen and water vapor

Hydrogen (H₂) is an important energy carrier, however, it can be hazardous owing to the risks involved with boring and explosion with colorless flames. By detecting the concentrations of H₂ and vapor water (H₂O) in real time, such risks can be prevented in advanced. In this study, a sensor system is developed based on photoacoustic spectroscopy using an H-type photoacoustic cell (PAC). Further, the time division multiplexing technique is used in a specific scanning period to realize dual-gas simultaneous detection. The dimensions of the PAC are optimized (inner volume: 1.8 cm³) and N-th characteristic frequencies are simulated through multiphysics simulation in COMSOL software. The optimized PAC is applied in the system and experiments of simultaneous dual gases detection are performed. The detection results show that the sensor's response time is 0.51 s and the recovery time is 0.38 s, and the minimal detection limit of H₂ is 138.69 ppm and H₂O can reach 3.70 ppm.     

The quantitative investigation of the lattice oxygen and grain edge oxygen on the thermal conductivity of aluminum nitride ceramics

The good thermal conductivity of AlN is essential for insulation and high heat dissipation applications. However, the influence of oxygen impurities at various locations (the lattice oxygen and grain edge oxygen) on the thermal resistivity of AlN ceramics is unclear. In this study, AlN ceramics with various oxygen distributions are prepared by different methods, and the oxygen contents of different regions are distinguished. The results indicate that the lattice oxygen is the main factor affecting thermal resistivity. Meanwhile, high-temperature annealing and pre-sintering processes can lower the lattice oxygen content from 0.061 wt% to 0.038 wt% and 0.036 wt%, respectively. Additionally, when grain edge phase volume is less than 4 vol%, it does not contribute significantly to thermal resistivity. The main formation of thermal resistance changes from phonon-defect scattering to phonon-phonon scattering with increasing temperature. These results may be informative for the microstructure design of AlN ceramics with high thermal conductivity.     

The high-temperature degradation mechanism of W-core SiC fibers

Continuous W-core SiC fiber has been regarded as a promising reinforcement, exhibiting huge potential for applying to hypersonic aircraft commonly suffering from harsh environment with high-temperature short-term characteristic. In this work, the micro/nano-scale investigation on heat treatment (HT) induced dynamic evolution of microstructure in W-core SiC fiber was performed to reveal strength degradation mechanism. It is revealed that the integrity of surface C coating can be well retained even after 1400 ℃/2 h HT avoiding the appearance of surface-dominated fracture mode. In the SiC sheath, only defects annihilation and crystallization transiting the disorder structure into well-crystallized β-SiC columnar grains instead of excessive growth happens, and thus HT induced sharp strength degradation cannot be governed by the microstructural variation of SiC sheath. After high-temperature HT, the interfacial reaction layer continuously thickens with increasing HT temperature that is proportional to fracture mirror zone radius, responsible for strength degradation induced by high-temperature short-term HT.     

Integrate design structure matrix with carbon footprint for product low carbon design

Product low-carbon design plays a significant part in reducing carbon footprint during the product life cycle. This paper proposed Design Structure Matrix integrated with Carbon Footprint (DSM-CF) to design for low carbon footprint. After the carbon footprint for product life cycle is discussed in detail, the DSM-CF is also proposed. The construction, decomposition and clustering algorithm of DSM-CF model is then put forward in detail. The impact of the carbon footprint of each design task on the entire product life cycle is analyzed, which could effectively reduce the carbon footprint of products. At the end of this paper, the DSM-CF model of the hand rehabilitation robot system is established to verify the effectiveness of the model.