Engineering reports : open access最新文献

Thermochemical water splitting stands out as the most efficient techniques to produce hydrogen through electrolysis at a high temperature, relying on a series of chemical reactions within a loop. However, achieving a durable thermochemical cycle system poses a significant challenge, particularly in manufacturing suitable coating materials for reaction vessels and pipes capable of enduring highly corrosive conditions created by high-temperature molten salts. The review summarizes thermally sprayed coatings (deposited on structural materials) that can withstand thermochemical cycle corrosive environments, geared towards nuclear thermochemical copper–chlorine (CuCl) cycles. An assessment was conducted to explore material composition and selection (structure–property relations), single and multi-layer coating manufacturing, as well as corrosion environment and testing methods. The aim was to identify the critical areas for research and development in utilizing the feedstock materials and thermal spray coating techniques for applications in molten salt thermochemical applications, as well as use lessons learnt from other application areas (e.g., nuclear reaction vessels, boilers, waste incinerators, and aero engine gas-turbine) where other types of molten salt and temperature are expected. Assessment indicated that very limited sets of coating-substrate system with metallic interlayer is likely to survive high temperature corrosive environment for extended period of testing. However, within the known means and methods, as well as application of advanced thermal spray manufacturing processes could be a way forward to have sustainable coating-substrate assembly with extended lifetime. Spraying multi-layered coating (nano-structured or micro-structured powder materials) along with the application of modern suspension or solution based thermal spray techniques are considered to result in dense microstructures with improved resistance to high temperature thermochemical environment.

The interest of this article is to obtain the underwater broadband sound absorption characteristics by filling three layers of bubbles in Polydimethylsiloxane polymer (PDMS). In this underwater ultra-thin metamaterial, three-layer bubbles are arranged from small to large with the same radius center. The finite element analysis (FEA) method and transfer matrix (TM) method have good consistency in calculating the sound absorption coefficient of this metamaterial. The results reveals that sub-wavelength metamaterial properties can be achieved below 6.4 MHz. Bubble coupling critical viscosity, waning coupling between layers, waveform transformation, and increasing scattering (reflection) waves all affect broadband sound absorption characteristics. The position and size of three bubbles are discussed, and design summary could be potentially in underwater ultrasound filter devices and medical ultrasound field.

This paper presents a high-gain wearable circularly polarized bow-tie antenna (WCPBTA) with metamaterial unit-cells and 5 pins (5Ps) technique for telemedicine applications such as telemonitoring the elderly or the patients especially for emergency conditions of contagious diseases. The frequency range of the proposed antenna is 5.725–5.850 GHz, which belongs to the unlicensed-national information infrastructure (U-NII-3) for the industrial, scientific, and medical (ISM) sub-channels. A light-weight and flexible felt with dielectric constant ε_r = 3, thickness 1.27 mm, and tan (δ) = 0.0095 is used as the substrate for patient comfort and wearability. The overall dimensions of the proposed antenna are 64 × 62 × 1.27 mm³ or 0.102 λ_g³ at 5.8 GHz. The maximum simulated gain at 5.8 GHz is 8.25 dB, which is more than 4 dB compared to that of the original bow-tie antenna. Besides, the axial ratio (AR) and the specific absorption rate (SAR) are also analyzed, which meet the perfect requirement for medical applications. The fabricated prototype of the antenna shows good compatibility between simulation and measurement results. These characteristics make the proposed WCPBTA a good choice for wireless body area networks (WBANs) in telemonitoring applications especially with the aim of preventing the spread of contagious diseases.

Blockchain (BCn) revolution across the world leads the global transformation by altering the existing structure and introducing the accessible and decentralized paradigm. This technology facilitates access to resources and redefines conventional frameworks, empowering people and communities globally. Motivated by these attention-seeking potentiality of BCn features, in this article, we examine the challenges, advancements, and emerging prospects of the BCn revolution in Bangladesh. With a specific focus on BCn implications for sustainability and smart development, this study addresses the urgent need to understand how BCn can facilitate sustainable development in rapidly evolving countries like Bangladesh. The goal of this research is to draw attention to the successful revolution of BCn in the world and use this knowledge to extract best practices and cutting-edge strategies for sustainable transformation of Bangladesh. The contribution of this study covers the underlying concepts of the BCn technology, showing the revolutionary state of BCn across the world, applications of BCn for sustainability, assessment of its current usage, and highlighting the BCn implementation problems. Furthermore, this study serves as a gateway to a transparent, decentralized future that fosters inclusive national progress and aligns with sustainable development goals. This study also strives to inspire individuals to use this transformational technology for the collective benefit of society by highlighting BCn's potential to empower communities while driving positive change.

MAX phases and their MXene compounds have received significant attention owing to their extensive potential applications. The quality and purity of the MAX phase guarantee the desired quality of the MXene product, which is essential for a variety of applications, including energy storage, catalysis, and electrical devices. Due to the purity, quality, complex structure, and unavailable commercial pure MAX powders, it is frequently required to have sophisticated synthesis and characterization techniques for the expected MAX products. Many researchers entering this field seek a comprehensive approach to the synthesis and characterization of MAX phases. Despite this, a significant portion of existing reviews have overlooked the synthesis and characterization methods specific to MAX phases, particularly when addressing MXenes. Consequently, this review aims to offer a thorough overview of the various synthesis methods and characterization techniques that are often required for MAX phases. In this review, various synthesis techniques, including their advantages and disadvantages, have also been discussed. Characterization techniques, especially x-ray diffraction (XRD), were found to be quite critical for new researchers. However, the integration of other techniques such as scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, and infrared analysis enhances and complements the findings obtained through XRD. The review also underscores the challenges associated with MAX phase synthesis and proposes potential solutions, emphasizing the assessment of their suitability across a broad spectrum of applications. Overall, this review serves as a comprehensive resource and guide for researchers engaged in the exploration and application of MAX phases, emphasizing the essential techniques of synthesis and characterization in harnessing their massive potential.

The effect of the initial atoms distribution on the molecular dynamics (MD) simulation of a model atomic fluid (argon) is investigated for the case of the isochoric phase transition to the supercritical state. In particular, the case of uniformly distributed atoms in the simulation domain is compared with the case of separated liquid and vapor atoms. The sensitivity of simulations to asymmetric nanoscale perturbations in the boundary is also studied. Despite its high computational cost, the MD approach has the potential to successfully address long-standing problems in computational fluid dynamics (CFD), especially those associated with mathematical singularities, such as contact angles, vortices, phase transitions and so forth. Unlike conventional CFD simulations, where the initial condition is the pressure or velocity distribution in the simulation domain, MD simulations also require the initial position of each molecule. Thus, it is important to understand whether a judicious choice of the initial distribution of molecules can reduce the overall computation time of the simulation. The evolution of the model fluid system during the phase transition was simulated using a Lennard-Jones interatomic potential, corrected with the Lorentz–Berthelot mixing rule for the interactions with the solid walls. The system was allowed to relax until equilibrium, and then a Heaviside temperature step was applied to the wall to bring the system to supercritical conditions. Results show the initial choice of the atoms distribution can significantly affect the computational time, while the effect of asymmetric perturbations on the boundary is negligible.

CO₂ flooding is an effective technology for suppling condensate gas reservoir pressure and mitigating global warming. In this study, numerical simulation studies have been conducted to enhance gas recovery in Pen5 condensate gas reservoir using CO₂ flooding. Pen5 reservoir has lasted 20 years of primary depletion, which affected by water invasion and retrograde condensation. In numerical simulation study, the GEM module is applied to implement history-matching of production data, and good agreement has been achieved. Based on comprehensive geological understanding, production dynamics, and numerical simulation techniques, areas with minimal impact from water invasion and retrograde condensation contamination have been delineated. The comparison between continued depletion and the implementation of CO₂ injection as a replacement technology in favorable areas has demonstrated the feasibility of CO₂ flooding development in these regions. The analysis of the advantages and disadvantages of using miscible flooding and immiscible flooding was conducted, and the optimal development well pattern was evaluated. In the end, the plan of CO₂ flooding of Pen5 reservoir has been designed and the gas production rate in the next 10 years has been predicted. The research findings of this study have reference significance for the practical application of CO₂ flooding in developing condensate gas reservoirs.

There is a growing concern about the environmental impact of the industrial and energetic sectors, which have been strongly dependent on fossil resources. Such dependence has caused an accelerated increase in the concentration of greenhouse gases in the atmosphere, contributing to global warming and the changes in worldwide weather patterns. Moreover, the continuous use of fossil sources causes a depletion in the availability of such non-renewable materials, reducing the opportunities for future generations to satisfy their basic needs. However, breaking this dependence on fossil resources is not easy since they are employed to produce a wide variety of derivatives such as fuels, chemicals, and energy, which are fundamental for the current lifestyle of a significant percentage of the world population.

Under such circumstances, biomass has been identified as a raw material with the potential to satisfy needs currently fulfilled through fossil sources. Biomass is the mass of all living beings. Thus, its composition includes carbon, as occurs with petroleum. Then, proper treatment can transform biomass into bio-based equivalents of petroleum derivatives. Moreover, biomass is renewable and widely available in different world regions. A fraction of the vegetable biomass is used as food; thus, its use for other applications is not adequate from an ethical perspective. However, another fraction is considered waste, including agricultural residues, organic municipal solid wastes, and industrial wastes. On the other hand, there are vegetable species that are not used as food sources or organisms that may generate compounds useful for society. Examples of these are the Jatropha species and the microalgal biomass. All these are examples of biomass whose composition has wide potential to obtain essential derivatives. Moreover, in the case of wastes, these are produced daily in high volumes. Their use as raw materials avoids inadequate disposal while generating valuable products, promoting the implementation of production schemes in a circular economy perspective.

Although the technologies to transform biomass into valuable products are already available, with some biorefineries currently operating in the world, there are still challenges that must be addressed. The most important one is related to economic factors. Bio-based products commonly have relatively high production costs, which are reflected in the final selling price. This may affect the implementation of a bio-based economy, mainly in countries with low incomes. Thus, research must continue to determine strategies to enhance the processes used for biomass conversion. For instance, fermentation-based processes usually have low yields and require relatively long periods to achieve their purpose. Thus, the development of modified organisms is an area of opportunity. Moreover, the purification of the products implies a high energy demand due to the highly diluted broths. Then, more effi

This study investigates the application of clustering techniques to enhance the accuracy of hierarchical classification and regression (HCR) models for predicting concrete compressive strength (CCS). Following the hypothesis that integrating clustering at the initial levels of model hierarchy reduces classification errors and prevents their propagation to subsequent levels, HCR models were developed utilizing both the unweighted pair group method with arithmetic mean (UPGMA) and hard clustering (HC) methods. Findings demonstrate that models using UPGMA significantly outperform those based on HC. Furthermore, it was demonstrated that further hierarchical clustering allows for multilayered HCR models that improve predictive performance by further leveraging parent–child relationships within data clusters. Overall, this study demonstrates that the proposed methodology can be introduced in the model development pipeline to enhance the prediction accuracy of CCS models.

The purpose of this study is to investigate the annual degradation rates of photovoltaic (PV) systems composed of PV modules based on recent crystalline silicon (c-Si) PV technologies. We investigated the annual degradation rates of four PV systems composed of different c-Si PV technologies, comprising p-type multi-crystalline silicon with a passivated emitter rear cell, n-type silicon heterojunction, p-type single-crystalline silicon (sc-Si) with an aluminum back surface field, and n-type (sc-Si) solar cell technologies. These systems were located in Gunma Prefecture in Japan and were measured over 6 years. Furthermore, the effects of soiling on the annual degradation rates of these PV systems were examined by partially surface cleaning the PV arrays two times. The results obtained indicate that the apparent annual degradation rates of the PV strings before surface cleaning were 0.8, 1.6, 1.4, and 1.2%/year, respectively, because of optical losses due to dust particles. However, the inherent annual degradation rates of the PV strings after surface cleaning were 0.1, 0.6, 0.0, and 0.3%/year, respectively. These low degradation rates indicate that the PV systems composed of the recent c-Si PV technologies all offered reasonably stable performance that was reduced by 3.6%, 5.5%, 7.3%, and 4.8%, respectively because of the effects of surface soiling, although the surfaces of the PV arrays had been washed by plentiful rainfall under their humid subtropical climatic operating conditions.