•Using multi-scale testing experiments to distinguish the aging mechanism and performance transformation.•Molecular dynamics simulation is carried out to explore the microscopic mechanism of the ...aging property transformation.•Corresponding relationship between macroscopic and microscopic performance is determined through comparative analysis.
As a complex mixed system, the aging mechanism of high-energy composite materials involves the aging of each component itself, interactions between components, and transformation of microstructural and thermodynamic properties. The study of a single component or performance parameter has great limitations for elaborating the cognitive complexity of aging processes, making it difficult to reveal the underlying principles of physicochemical property transformation. Thus, it can only be applied as an empirical summary. In view of this, this study comprehensively utilized numerical analysis and experimental detection to explore the evolution of micromolecular conformation and changes in macro aging performance from four aspects of composite systems, including binder aging, plasticizer migration, bond interface debonding, and mechanical property transformation. There was good consistency observed between molecular simulation and thermal aging experiments, indicating that there was basically no post curing process for HTPB propellants using TDI as the curing agent. In the early stage of aging, scission chain was the main process and, in the later stage of aging, oxidation crosslinking the main process. Oxidative crosslinking increased the mean square radius of gyration and glass transition temperature of the binder system, reduced the peak value of radial distribution function, and revealed the reason for the change of propellant hardness and CC and CO double bond content. However, chain degradation increased the number of polar groups, enhanced intermolecular polarity, reduced the solubility parameter, and increased the free volume fraction of the mixed system and the dioctyl sebacate diffusion coefficient. This resulted in an increase in the tangent value of the HTPB propellant loss angle from 0.43 to 0.44° and a decrease in the glass transition temperature from 203.3 to 202.0 K. The binding energy at the interfaces of AP/HTPB and Al/HTPB increased first and then decreased, which was consistent with SEM images of bonding interfaces. The joint effect of binding energy and mechanical properties of the binder system promoted the transformation of the stress-strain curve of aging propellant.
In recent years, ground source heat pump systems are recognized as effective renewable energy heating, ventilation and air-conditioning systems. In ground source heat pump systems, ground heat ...exchangers serve as heat-conducting medium with vertical distribution or horizontal distribution. Many remarkable studies were carried out in the past few years. However, most of the existing reviews mainly contributed to vertical ground heat exchangers research along with design, performance, and applications. A systematic summary on analyzing thermodynamic performance of horizontal ground heat exchangers in ground source heat pump systems is essential. Therefore, this review aims to summary the optimal thermodynamics analysis on horizontal ground heat exchangers in ground source heat pump systems. According to the analytical solutions, numerical simulations and experimental measurements, the reviewed research articles are classified into four sub-categories: linear-loops, slinky-coils, helical-coils and others. The optimal thermodynamic performance for each study is illustrated and discussed. Furthermore, assessments and comparisons among different horizontal ground heat exchangers are summarized. In the end, future development suggestions and research direction recommendations related to ground source heat pump systems with horizontal heat exchangers are given.
•Summarizes analysis methodologies for HGHEs in GSHP systems including energy, exergy and heat transfer approaches.•Reviews optimal thermodynamic analysis on various HGHEs by appropriate classifications.•Reviews the comparison among different HGHE configurations.
Wet particle fluidization is commonly applied in some industries such as catalytic cracking, pharmaceutical manufacturing, mineral processing, food drying, etc. Understanding the within fluidization ...characteristics is important for the scale-up, design and optimization of industrial process. This article reviews the recent studies on fluidization characteristics of wet particles in fluidized beds and spouted beds. Both physical experiment and numerical simulation results are included. For physical experiments, the focus is on the development of new measurement methods and the resulting findings. For numerical simulations, the focus is especially on the development of the discrete element method (DEM) which can lead to new insights for wet particle fluidization at particle scale. Finally, challenges and needs for future research on wet particle fluidization are discussed.
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•Refined methods for the accurate acquisition of crack measurements are proposed.•Crack locations and crack kinematics are automatically extracted from DIC results.•The procedure ...captures the complete crack behaviour in large-scale concrete tests.•The statistical consolidation to characteristic crack properties is proposed.•The procedure is implemented in a user-friendly open-source tool.
The accurate extraction of the crack patterns and measurements of crack kinematics are essential for understanding the mechanical behaviour in experiments on structural concrete as well as in the validation and further development of sound mechanical models. This paper presents important refinements of the authors' recently published automatic crack detection and measurement procedure (ACDM) based on surface displacement measurements obtained with digital image correlation (DIC). The proposed refinements are crucial for reliably assessing the crack behaviour in large-scale experiments with complex crack patterns, since the original methods of ACDM may fail or result in biased measurements at locations with closely spaced cracks, crack intersections or cracks with high morphological curvature. The main refinements are (i) a Canny edge-based crack detector, which is applied on the DIC major principal strain field and (ii) enhancements in the crack kinematic measurement to assess the reliability of the results. The latter includes the automatic selection of optimum reference points used in the crack kinematic measurement to increase its reliability and remove uncertain results. The refined ACDM procedure is validated using several large-scale 2.0 × 2.0 m shear panel experiments with highly complex crack patterns. Compared to the original ACDM, significantly thinner cracks can be detected with a much higher reliability of crack locations and crack kinematic measurements, particularly close to crack intersections and at closely spaced cracks. Additionally, two approaches for the statistical consolidation of the large amount of gathered data into characteristic crack properties in large-scale homogeneous concrete element experiments are proposed and compared. The results show that the statistical consolidation of the ACDM data using a 95%-quantile match well with the direct extraction of the best-fit homogeneous crack properties from the full-field DIC displacements. The consolidated data provides highly valuable insight into the mechanical behaviour, especially regarding crack phenomena.
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•The AnTLcirCapValVis analytical apparatus was applied to carry out the measurements.•The VLE data for the two binary systems (R125 + R1234yf and R125 + R1234ze(E)) were measured at ...five temperatures.•The experimental VLE data were correlated by the PR-type + WS + NTRL models.•The systems exhibited zeotropic behavior at the studied temperatures.
In this work, isothermal vapour-liquid equilibrium (VLE) data for the binary mixtures of pentafluoroethane (R125) + 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) and trans-1,3,3,3-tetrafluoropene (R1234ze(E)) have been investigated. The experimental measurements were carried out by using the AnTLcirCapValVis analytical method over the temperature range from 283.15 K to 323.15 K. The standard uncertainties of temperature, pressure and mole fractions are 10 mK, 0.5 kPa and 0.005, respectively. The Peng-Robinson (PR) equation of state (EoS) and its modifications from Stryjek and Vera (PRSV and PRSV2) combined with Wong-Sandler (WS) mixing rule and the non-random two-liquid activity coefficient model (NRTL) were employed to correlate the parameters of binary mixtures, respectively. The PRSV2 + WS + NRTL model shows the best consistency with the experimental VLE data compared with the other two models (PR + WS + NRTL and PRSV + WS + NRTL). The average absolute relative deviation of pressure (AARD(p)) and average absolute deviation of vapour phase mole fraction (AAD(y)) are 0.10% and 0.0012 for R125 + R1234yf, 0.16% and 0.0014 for R125 + R1234ze(E), respectively. Both the experimental data and the calculated results imply that R125 + R1234yf and R125 + R1234ze(E) are zeotropic binary mixtures over the studied temperatures.
As follow-up efforts for measurements on emission factors (EFs) of fine particulate matter (PM2.5) and its carbonaceous fractions for China's household coal stoves, a large-sized dilution sampling ...system was designed to test a total of 20 coal/stove combinations, which involve five coals with wide-ranged geological maturities and three stoves. Coal smoke was simultaneously collected onto quartz filter for organic carbon (OC) and elemental carbon (EC) analyses by thermal-optical reflectance (TOR) protocol and monitored online for optical black carbon (BC) by Aethalometer. The mean EFs based on burned fuel weight of PM2.5, OC, EC, and BC are 4.25 ± 2.45, 1.11 ± 0.72, 1.43 ± 1.17, and 0.60 ± 0.42 g/kg for bituminous coal, and 1.44 ± 0.67, 0.05 ± 0.02, 0.04 ± 0.02, and 0.01 ± 0.01 g/kg for anthracite, respectively. Significant differences are observed among the EFs for various coal/stove combinations, which are attributable to the differences of coal maturity, burning style and stove efficiency. Although the EFs of BC and EC are closely correlated (r = 0.97), the average BC/EC ratio is only 0.39, indicating a significant gap between the two methods; and the optical attenuation cross-section (σ) for fresh coal smoke can be deduced as 6.47 m2/g, much lower than the manufacturer's preset value of 16.6 m2/g for Aethalometer.
•Carbonaceous particulate matter emission factors among 20 coal/stove combinations.•Dominating factors are coal maturity, burning style and stove efficiency.•Optical attenuation cross-section for fresh coal smoke can be deduced as 6.47 m2/g.
Objective: Understanding the in vivo force and tissue dimpling during micro-electrode implantation into the brain are important for neuro-electrophysiology to minimize damage while enabling accurate ...placement and stable chronic extracellular electrophysiological recordings. Prior studies were unable to measure the sub-mN forces exerted during in vivo insertion of small electrodes. Here, we have investigated the in vivo force and dimpling depth profiles during brain surface membrane rupture (including dura) in anesthetized rats. Methods: A μN-resolution cantilever beam-based measurement system was designed, built, and calibrated and adapted for in vivo use. A total of 244 in vivo insertion tests were conducted on 8 anesthetized rats with 121 through pia mater and 123 through dura and pia combined. Results: Both microwire tip sharpening and diameter reduction reduced membrane rupture force (insertion force) and eased brain surface penetration. But dimpling depth and rupture force are not always strongly correlated. Multi-shank silicon probes showed smaller dimpling and rupture force per shank than single shank devices. Conclusion: A force measurement system with flexible range and μN-level resolution (up to 0.032 μN) was achieved and proved feasible. For both pia-only and dura-pia penetrations in anesthetized rats, the rupture force and membrane dimpling depth at rupture are linearly related to the microwire diameter. Significance: We have developed a new system with both μN-level resolution and capacity to be used in vivo for measurement of force profiles of various neural interfaces into the brain. This allows quantification of brain tissue cutting and provides design guidelines for optimal neural interfaces.
•A new transient hot-wire thermal conductivity apparatus was built.•Thermal conductivity measurements were conducted on helium within 20–300 K.•The experimental results agreed well with the model ...calculation and numerical simulation results.
In this study, an apparatus based on the transient hot-wire method (THW) was designed to measure the thermal conductivity of cryogenic fluid within the temperature range of 20–300 K and the pressure range of 0–20 MPa, with a relative expanded uncertainty Ur(λ) of 0.0284 (k = 2, 95 %). The experimental data of methane, ethane, and carbon dioxide showed good consistency with the ECS model, validating the reliability of the apparatus. In addition to the linear temperature dependence of hot-wire resistance above 70 K, the nonlinear temperature dependence below 70 K is calibrated, and the feasibility of the THW method for measurements in the temperature range of 20–70 K is validated. Subsequently, the thermal conductivity data for helium are presented from 20 to 300 K. The temperature rises of hot-wire during the measurement agreed well with the simulation calculation results. Furthermore, a thermal conductivity model for helium gas up to 600 K was developed. The presented data in this work, as well as previously published data, demonstrated good agreement with the model calculation results, with an average absolute relative deviation (AARD) of 1.46 %.
In this study, the numerical analysis and experimental measurements are conducted on the internal flow field and temperature distribution of ejectors with different throat diameters. The ...computational fluid dynamics (CFD) is used to simulate different ejectors and investigate the effects of Mach number, pressure, and temperature distributions. The hydrogen Entrainment Ratio (ER) of ejectors is also measured for proton exchange membrane fuel cell applications. The experimental measurements and simulations of the hydrogen Entrainment Ratio of the ejectors showed that the recovery efficiencies are 59%, 53%, and 33% for the pipe diameters of 0.5, 0.7, and 1.0 mm at the inlet pressures of 340 kPa, respectively. In different area ratios, the larger area ratio of the nozzle leads to greater difference between the diameter of the throat and the diameter of the throat outlet. This causes a smaller recovery rate. In the internal flow field of the ejector, higher recovery rate can be achieved by using the closer location of the positive shock wave to the nozzle outlet.
•The ejectors with different throat diameter designs are created.•The larger the area ratio of the nozzle resulting in a smaller recovery rate.•The 0.5 mm diameter ejector has higher hydrogen recovery rate.
In this paper, the variation of surface tension coefficient of water magnetized by a solenoid coil was studied by experimental measurement. It was found that the surface tension coefficient of pure ...water decreased after the magnetization treatment, and the decrease ratio depends on the magnetic field intensity and the treatment time exposed in the magnetic field. The maximum decrease of about 25% (from 72 mN/m of pure water to 54 mN/m) occurs at magnetic field intensity of 300 mT and treatment time of 15 min. However, the surface tension coefficient of magnetized water does not keep stable at the low value, it returns to the original value gradually in about 1 h.
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