•Blast testing on high strength reinforced columns.•Blast testing on ultra high performance fibre reinforced concrete columns.•Large axial loading is applied on columns during the blast tests.
Ultra ...high performance fibre reinforced concrete (UHPFRC) is a cement-based composite material mixing with reactive powder and steel fibres. It is characterized by its high strength, high ductility and high toughness and such characteristics enable its great potential in protective engineering against extreme loads such as impact or explosion. In the present study, a series of field tests were conducted to investigate the behaviour of UHPFRC columns subjected to blast loading. In total four 0.2m×0.2m×2.5m UHPFRC columns were tested under different designed explosions but all at a standoff distance of 1.5m. Blast tests were also performed on four high strength reinforced concrete (HSRC) columns with the same size and reinforcement as UHPFRC columns to evaluate their behaviour under the same loading conditions. The data collected from each specimen included reflected overpressures, column deflections at centre and near the supports. Three major damage modes, including flexural, shear and concrete spalling failure modes, were observed. The post blast crack patterns, permanent deflections and different levels of damage observations showed that UHPFRC columns performed superior in blast loading resistance as compared with HSRC columns.
Membrane is one of the most important components in proton exchange membrane fuel cells (PEMFCs), which determines the transport phenomena, performance, and durability. With the rapid development of ...novel membranes, many transport coefficients in membranes applied in numerical studies are outdated due to the lack of experimental data for new membranes. In this review, the fundamentals of commercially available membranes are scrutinized, followed by the fundamental working mechanisms. A detailed examination of the transport phenomena within the membranes, including transport mechanisms, mathematical description, and experimental methods, is conducted for protonic conduction, electro-osmosis drag, diffusion, hydraulic permeation, and gas crossover, which are urgently needed for theoretical and numerical studies. It is found that various empirical or analytical correlations have been established to predict the transport coefficients of the membranes. However, empirical models may not be accurate for all types of membranes since there is no sufficient experimental data for a solid correlation and validation. The experimental methods reviewed in the present study can be applied for new membranes, which is essential to quantify the transport phenomena and its further impact on cell performance and durability. The key transport-phenomena-related factors that affect the performance and failure modes of membranes are also reviewed in this study, which helps to develop strategies in improving membranes’ performance and durability during operation. This review deepens the understanding of the short-term and long-term performance of the membrane in PEMFCs and provides important insights into the further design of novel membranes.
•Scrutinized fundamental concepts and recent progress in membranes of PEMFCs.•Reviewed the transport phenomena in membranes of PEMFCs.•Summarized the transport coefficients and experimental methods for membranes.•Evaluated the effect of transport-phenomena-related factors on membrane performance.•Reviewed the effect of transport-phenomena-related factors on membrane durability.
In this work, a peridynamics-based representative volume element approach is implemented to estimate the effective tensile modulus of nanomodified epoxy resins. The results obtained through this ...homogenization procedure are then used as input for the analysis of nanocomposite fracture toughness, which is carried out by exploiting a classical continuum mechanics-peridynamics coupling strategy. In the coupled model, the small-scale heterogeneity of the crack tip region is preserved by implementing the recently proposed intermediately-homogenized peridynamic model. Comparison to experimental data confirms the capability of the peridynamics-based approaches to properly model the effective tensile modulus and fracture toughness of polymer-based nanocomposites.
•Nanocomposite effective tensile modulus is derived through a PD-based RVE homogenization.•RVE homogenization results are used as input for the fracture toughness analysis.•Effect of nanomodification on the fracture toughness is studied through a FEM-PD coupling strategy.•PD-based approaches operate at different length scales.•Numerical results are calibrated by performing tensile tests and mode I fracture tests.
Dissolution trapping is one of the primary mechanisms that enhance the storage security of supercritical carbon dioxide (scCO2) in saline geologic formations. When scCO2 dissolves in formation brine ...produces an aqueous solution that is denser than formation brine, which leads to convective mixing driven by gravitational instabilities. Convective mixing can enhance the dissolution of CO2 and thus it can contribute to stable trapping of dissolved CO2. However, in the presence of geologic heterogeneities, diffusive mixing may also contribute to dissolution trapping. The effects of heterogeneity on mixing and its contribution to stable trapping are not well understood. The goal of this experimental study is to investigate the effects of geologic heterogeneity on mixing and stable trapping of dissolved CO2. Homogeneous and heterogeneous media experiments were conducted in a two‐dimensional test tank with various packing configurations using surrogates for scCO2 (water) and brine (propylene glycol) under ambient pressure and temperature conditions. The results show that the density‐driven flow in heterogeneous formations may not always cause significant convective mixing especially in layered systems containing low‐permeability zones. In homogeneous formations, density‐driven fingering enhances both storage in the deeper parts of the formation and contact between the host rock and dissolved CO2 for the potential mineralization. On the other hand, for layered systems, dissolved CO2 becomes immobilized in low‐permeability zones with low‐diffusion rates, which reduces the risk of leakage through any fault or fracture. Both cases contribute to the permanence of the dissolved plume in the formation.
Key Points:
Diffusion can be the dominant mixing mechanism in low‐permeability zones
Low‐permeability zones can immobilize dissolved mass for stable trapping
In blocks heterogeneity, spreading depends on the permeability distribution
•We show the limitations of existing Capacitated Vehicle Routing Problem instances.•We propose 100 new instances and evaluate recent exact and heuristic methods.•The same generating scheme is used to ...create an extended benchmark of 600 instances.•Extensive experiments and statistical analyses are done on the extended benchmark.•We present a sophisticated website containing all existing and new instances.
The recent research on the CVRP is being slowed down by the lack of a good set of benchmark instances. The existing sets suffer from at least one of the following drawbacks: (i) became too easy for current algorithms; (ii) are too artificial; (iii) are too homogeneous, not covering the wide range of characteristics found in real applications. We propose a new set of 100 instances ranging from 100 to 1000 customers, designed in order to provide a more comprehensive and balanced experimental setting. Moreover, the same generating scheme was also used to provide an extended benchmark of 600 instances. In addition to having a greater discriminating ability to identify “which algorithm is better”, these new benchmarks should also allow for a deeper statistical analysis of the performance of an algorithm. In particular, they will enable one to investigate how the characteristics of an instance affect its performance. We report such an analysis on state-of-the-art exact and heuristic methods.
The search for photocatalysts allowing the highly active, selective, and stable conversion of molecular oxygen into hydrogen peroxide is of worldwide interest. Here, the authors report the efficient ...conversion of O2 into H2O2 with ≈100% selectivity and stable cycle stability by a triphasic metal oxide photocatalyst with a cobalt hydroxide carbonate nanosheet phase for water oxidation as well as iron oxide and titanium oxide phases of a core‐shell morphology for charge transfer and oxygen reduction, denoted as CFT. The different surface energies of 0.78 (anatase) and 0.93 J m‐2 (rutile) for titanium oxide and 1.39 J m‐2 for iron oxide result in a core‐shell morphology. The band gaps for iron oxide (2.02 eV), titanium oxide (≈3 eV), and cobalt hydroxide carbonate (3.80 eV) sites reveal that the CFT photocatalyst allows visible‐to‐UV light absorption. The 18O2 isotope‐labeling experiments prove that the core‐shell structure promotes hole transfer toward the water oxidation site. Additionally, the hole‐induced H2O2 decomposition at the oxygen reduction site is efficiently hindered. Moreover, the photogenerated electrons transfer toward the oxygen reduction site to produce H2O2 from O2 with ≈10‐fold higher activity than those by conventional single‐ or dual‐phase photocatalysts, while giving robust cycle stability.
The authors report that a triphasic metal oxide photocatalyst with water oxidation (Co2(OH)2CO3), electron/hole transfer (Fe3O4), and oxygen reduction (amorphous TiO2) sites allows the highly active and selective conversion of O2 into H2O2. These sites lead to about tenfold higher activity than single‐phase or dual‐phase photocatalysts, and ≈100% selectivity using only water and solar energy without sacrificial reagents.
Air-cooled proton exchange membrane fuel cells (PEMFCs) have the advantages of simple structure, low parasitic power, and flexible application scenarios. However, it is difficult to warm up the stack ...under subzero temperatures because excessive air is used as the cooling medium. In this study, the thermal balance inside an air-cooled PEMFC stack during cold start was theoretically analyzed to explore the relationship between the heating power and ambient temperature. Subsequently, the cold-start performance was tested in a climatic chamber. The results showed that the combination of endplate heating and gas heating is a feasible cold-start measure. The theoretical analysis indicated that only 14 % of the stack rated power for preheating can promote a successful cold start at −30 °C, which has also been validated in the ensuing tests. The test results showed that the temperature uniformity and the cell voltage consistency deteriorate as the ambient temperature decreases, while these two indicators can be improved by increasing the gas heating power. As the ambient temperature decreases, the heating power may become too high, resulting in poor cold-start performance. Therefore, if an air-cooled stack is to be started at extreme low temperatures, further research is needed in terms of flow fields and materials.
•MWCN-reinforced polymer composite frequency computed using the HSDT model.•The nanotube composite properties are computed theoretically assuming the random distribution via Mori-Tanaka scheme and ...experimentally.•The desired responses are computed via computer code and compared with experimental frequencies for the validation purpose.
The vibration frequencies of multi-walled carbon nanotube-reinforced polymer composite structure are examined numerically via a generic higher-order shear deformation kinematics for different panel geometries. The extensive behaviour of the current higher-order model is demonstrated by comparing the results with the published data including the own in-house experimental values. In this analysis, the required elastic properties of the randomly distributed nanotube-reinforced polymer composite panel are evaluated numerically using Mori–Tanaka scheme. Firstly, the equation of motion of the vibrated nanotube composite panel derived via the classical Hamilton's principle and the isoparametric finite element steps are implemented for the numerical purpose. Further, the modal responses are obtained computationally using an original computer code (MATLAB) with the help of the higher-order finite element formulation. The necessary convergence and subsequent comparison have been made for the presently developed numerical model with those available published results including the values obtained via commercial package (ANSYS). Additionally, the model validation has been established by comparing the present numerical frequency values with the lab-scale free vibration experimental data. The specific conclusions are drawn by examining different numerical examples for various structural parameters using the experimental properties.
Display omitted The vibration frequencies of MWCN–reinforced composite panel is computed theoretically using the presently developed higher–order kinematic theory and compared with available experimental results for the validation purpose. The MWCN reinforced composite plate is fabricated using hand layup technique and frequency values are recorded via cDAQ in association with LabVIEW.
•Comparative experimental analysis of 2 double-channel solar air heater with and without PCM was accomplished.•Experimental campaign was executed for both collectors simultaneously for three ...different environmental conditions.•General operation of collector with PCM is better compared with traditional device without PCM.
This work presents an experimental analysis of a double-channel solar air heater (SAH) with and without phase-change material (PCM) as thermal energy storage system (TES). Two identical prototypes were designed and constructed, and one of them was modified to house macro- encapsulated PCM in the absorber plate. Both collectors were evaluated in an experimental setup instrumented for hot air temperature and velocity, solar radiation, temperature probes in the glass cover, absorber plate, PCM storage system, and a weather station to record the environmental conditions. To evaluate the performance of the SAH under sudden variations of solar radiation, three different case studies were considered with varying conditions of weather: clear sky and high radiation, partially cloudy, and clear sky with a substantial drop in solar radiation at noon. The maximum outlet temperatures reached by the SAH with PCM were 82 °C, 62 °C, and 79.5 °C for the three cases, respectively. The outlet temperature of the SAH without PCM was consistently 10 °C lower compared to the collector with PCM. The PCM maintained the heating during day irradiation transients and extended it after dusk, without any decrease in the thermal efficiency. Further studies of modeling and design optimization appear very pertinent.
This research paper presents numerical and experimental investigations to examine the effectiveness of a honeycomb pattern as a form of the geometry of artificial roughness in solar air heaters. ...Utilizing Computational Fluid Dynamics (CFD) through three-dimensional simulations, the study explores how Thermo-Hydraulic Performance Parameter (THPP) is affected by variations in honeycomb geometry. The research examines various parameters, including the angle of attack (Ø), relative roughness pitch (P/e), and relative roughness height (e/D) within the respective ranges of (90°-120°), (8–12), and (0.03–0.05). The system's performance is evaluated across various flow scenarios, covering Reynolds numbers from (3000) to (21,000). Incorporating the honeycomb design into an absorber is observed to improve the heat transfer rates. The system achieves a maximum Nu of (140.65) at (e/D) of 0.04, (P/e) of 10, (Ø) of 120°, and Re of (21,000). The maximum FF of (0.039) was obtained at (e/D) of 0.05, (P/e) of 9, and (Ø) of 120° at a Reynolds number of (6000). The system exhibited a THPP of (1.7) at a Reynolds number of (6000). This Maximum THPP was associated with specific parameters, including (e/D) of 0.04, (P/e) of 10, and (Ø) of 120°.
Display omitted
•Numerical investigations followed by experimental validations.•Honeycomb-shaped artificial roughness improved the heat transfer rates.•The thermo-hydraulic performance parameter achieved a maximum value of (1.7).
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