Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Erosion behaviour of Fe-Cr-C alloys: Cast alloy versus coating
No full textThis research focuses on the erosion wear behaviour of two Fe-Cr-C alloys with similar chemical compositions obtained using different production methods. The first alloy belongs to the high chromium cast irons (HCCI). It was made by casting, after which the samples were heat treated by annealing. The second alloy in the form of the coating was applied by the plasma transferred arc (PTA) surface welding process at the substrate material (structural carbon steel). Damage to the components of industrial plants due to erosive and/or abrasive wear is a frequent cause of failure and outages of such systems. For this reason, and to bring the experimental research closer to real service conditions, an erosion test was performed at a gas blast sand facility with a high erodent speed of 90 m/s and a higher feed rate than standard erosion testing parameters recommended in ASTM G76 standard. Microstructural characterisation of all samples was done using a scanning electron microscope (SEM). The X-ray diffraction analysis (XRD) was used to identify the phases present. Similar erosion mechanisms were observed on all tested specimens, but coated samples (PTA alloy) had a lower mass loss during the erosion test compared to cast samples (HCCI alloy), i.e. they showed better erosion resistance
OpenFOAM NUMERICAL SIMULATION AND EXPERIMENTAL VALIDATION OF HIGH CAPACTY LONG DISTANCE FLY ASH PNEUMATIC CONVEYING FROM A 620 MW THERMAL POWER PLANT
No full textThe authors conducted pressure drop numerical simulations of multiphase gas-solid flow characteristics, within a fly ash pneumatic conveying system, in 620 MW thermal power plant. The objective of this study is to verify the OpenFOAM model by comparing the numerical results with pressure measurements taken along the considered pipeline. The numerical model is developed on the base of extensive experimental research of high-capacity long-distance pneumatic conveying system for Kolubara lignite fly ash. The numerical simulations of pneumatic conveying were performed using the Euler-Euler approach in OpenFOAM, that is twoPhaseEulerFoam solver, for the air mass flow rate of 5500 Nm3/h, the fly ash mass flow rate 77 t/h. The calculation input air pressure at the pipeline outlet was assumed to be as measured approximately 234 kPa, the air-ash mixture temperature was 373,15K, the mean ash particle diameter of 0.128 μm, and physical density of ash 2100 kg/m3. Numerical mesh is generated as an O-grid for the first two pipeline sections, first with a length of 90 m, a diameter of 0.2604 m, and an inclination of 1.885 degree, and the second with a length of 102 m, a diameter of 0.3097 m, and an inclination of 2.163 degree, while every mesh cell is substantially larger than the diameter of the ash particle. The applied Euler-Euler approach enables a comprehensive investigation of the complex dynamics involved in pneumatic conveying, considering the two-phase nature of the system and providing valuable insights into the particle behavior, pressure drop, and other key parameters. The comparison of the experimental and numerical model simulations data show good agreement regarding pressure drop. Although Euler-Euler model is complex in terms of necessary closure models, it might prove itself as reliable for simulated conditions in future studies
APPLICATION OF 3D PRINTING IN ORTHOPEDICS
No full textThe integration of 3D printing technology into orthopedic practice addresses the critical problem of enhancing surgical precision and improving patient-specific treatment. Traditional orthopedic methods often involve generic implants and extensive preoperative planning, which can lead to suboptimal fit, prolonged surgery times, and varied patient outcomes. To solve this problem, patient-specific 3D anatomical models and custom implants can be used. High-resolution imaging data from patients can be converted into 3D-printed models, allowing for detailed preoperative planning and the creation of implants tailored to individual anatomical structures. This method also uses biocompatible materials and advanced printing techniques to ensure structural integrity and functionality. The use of 3D-printed models facilitated an enhanced preoperative understanding of complex anatomies, leading to reduced operative times and increased surgical precision. Customized implants result in better fit and integration with the patient's body, contributing to faster recovery times and higher patient satisfaction. Case studies indicate that this approach minimizes complications and optimizes overall orthopedic care. Despite promising results, challenges such as regulatory limitations, cost considerations, and the need for interdisciplinary collaboration remain. However, ongoing research and technological developments are expected to further refine these applications, paving the way for greater adoption and more widespread benefits in orthopedic practice
Developing thermal insulation cement based mortars with recycled aggregate in accordance with Net Zero principles
Get PDFThe performance of thermo insulation rendering mortars with alternations in ratios
of powdered cordierite and talc was examined. The goal was to confirm that recycled
kilnware cordierite can be reapplied in the mortar design without significant deterioration in
performance in comparison with OPC mortar. Differential thermal analysis was employed for
examining thermally induced reactions. The ca vitation erosion, in testing sequences ranging
from 30 to 120 minutes, was used to assess the compa ctness of the mortar structure. The
physico mechanical properties of experimental mortars were investigated. The morphologies
of the mortar tablets upon cavi tation were studied using a scanning electron microscope. It
was established that cordierite and talc filler in amounts up to 20% enhance microstructural
packing and mechanical strengths due to improved cementation and therefore contribute to
cavitation er osion resistance. Hig her amounts of talc cause structural degradation and mass
loss during cavitation tests. Reducing manufacturing costs, energy consumption, and
greenhouse gas emissions are the main objectives of t he production of this waste based
constr uction composite, as the reuse of waste materials can help achieve a number of
Sustainable Development Goals
Merging Eco-Art and Recycling to Advance Environmental Preservation
No full textEco-art and recycling initiatives often involve comprehensive community engagement and participation in specific conditions. This paper explores the synergy between eco-art and recycling processes, as an optimal strategy to advance environmental preservation, alongside the integration of land art with ecological concepts. As environmental concerns escalate, the integration of ecoartistic measures and practices with recycling initiatives emerges as a potential to enhance environmental consciousness and sustainability. The study delves into the interconnectedness of these two disciplines, examining how the creative expression of eco-art can amplify the impact of recycling efforts and activities, leading to heightened environmental awareness and conservation. By detailed examination of the intersections of these creative and ecological disciplines, the research aims to contribute insights into innovative approaches that simultaneously harmonize artistic expression and environmental conservation aspect, with the final important task of protecting our planet and ensuring sustainable development
Application and characterization of a kerosine-fuelled High Velocity Oxy-Fuel (HVOF) Ti2AlC coating on thermally stable P91 steel
Get PDFA class of ternary layered carbides and nitrides, known as MAX
phases, combines some of the best properties of two distinct
classes of materials: metals and ceramics. Specifically, MAX phases
are stable at high temperatures, resist thermal shock, and some
even form stable and protective oxide layers in oxidizing environments.
Thus, they are excellent candidates for protective coatings
in high-temperature applications. In this context, our focus is on
using kerosene-fueled High-Velocity Oxy-Fuel spraying to deposit
MAX phases onto P91 steel substrates for use as thermal barrier
coatings. The chosen MAX phase for this study is Ti2AlC, which
offers an outstanding oxidation resistance. Our results indicate that
during the spraying procedure, a portion of the MAX phase decomposes,
another portion oxidizes, yet more than half maintains the
initial and desired stoichiometry. Nevertheless, the resulting coating
establishes a stable and robust bond with the steel substrate. In this
presentation, we will discuss the detailed analysis concerning the
relationship between the process, structure, and performance of the
Ti2AlC coating on the P91 steel substrate
Comparative Studies of the Structural and Physicochemical Properties of the First Fullerene Derivative FD-C60 (Fullerenol) and Second Fullerene Derivate SD-C60 (3HFWC)
Get PDFIn order to maximally reduce the toxicity of fullerenol (the first derivative of C60, FD-C60), and increase its biomedical efficiency, the second derivative SD-C60 (3HFWC, Hyper-Harmonized Hydroxylated Fullerene Water Complex) was created. Several different methods were applied in the comparative characterization of FD-C60 and SD-C60 with the same OH groups in their core. FD-C60 as an individual structure was about 1.3 nm in size, while SD-C60 as an individual structure was 10–30 nm in size. Based on ten physicochemical methods and techniques, FD-C60 and SD-C60 were found to be two different substances in terms of size, structure, and physicochemical properties; FD-C60, at 100 °C, had endothermic characteristics, while SD-C60, at 133 °C, had exothermic characteristics; FD-C60 did not have water layers, while SD-C60 had water layers; the zeta potential of FD-C60 was −25.85 mV, while it was −43.29 mV for SD-C60. SD-C60 is a promising substance for use in cosmetics and pharmaceuticals
Energy Efficiency in Serbia: Challenges and Opportunities
No full textEnergy efficiency plays a critical role in achieving economic, social, and environmental sustainability. This paper provides an overview of the current state of energy efficiency in Serbia, focusing on the challenges, opportunities, and potential pathways towards a more sustainable energy sector. The country has recognized the importance of energy efficiency in improving energy security, reducing costs, and complying with international environmental standards. However, Serbia faces significant challenges, including a lack of awareness of the benefits of energy efficiency, insufficient financing, and policy support for energy-efficient technologies. Nevertheless, Serbia possesses considerable potential for energy-efficient technologies and practices, particularly in the residential and industrial sectors. By promoting energy efficiency, Serbia can reduce energy costs, improve energy security, and contribute to global climate-change mitigation efforts. The paper also highlights the global challenges faced by the energy sector, such as rising energy demand, climate change, pollution reduction, and energy poverty, emphasizing the need for greening the energy sector and investing in renewable energy sources. The energy consumption trends, energy intensity, energy productivity, and share of renewable energy sources in Serbia were analyzed using EuroStat data. The paper concludes by emphasizing the importance of ambitious goals, public awareness, modernizing infrastructure, and securing adequate financing to drive energy efficiency improvements in Serbia. This overview serves as a valuable resource for policymakers, researchers, and stakeholders interested in promoting sustainable energy practices in Serbia and fostering a transition towards a more energy-efficient and environmentally friendly energy sector
Numerical and analytical modeling of a shaped charge penetration depth
Get PDFShaped charge effect have been successfully used in various fields, including defense (anti-armor projectiles and warheads) and non-military (explosive demolitions, oil and natural gas industry) applications. The shaped charge mechanism relies on conversion of explosive charge detonation energy into kinetic energy of a hypervelocity metal penetrator, known as a jet [1]. The focus of the present research is on the jet interaction with the target material and consequent target penetration.
Two approaches to the jet penetration depth determination are considered. The first is the well-known analytical model based on the virtual origin concept [2, 3]. The second approach is the numerical modeling of the penetration process. The commercial FEM based software Abaqus/Explicit has been used for simulations and the model formulation is described in detail. The complete process of the shaped charge jet formation and penetration is successfully simulated using the pure Eulerian approach with appropriate material models [4].
Comprehensive comparison between results obtained using various theoretical models (analytical and numerical) and experimental data has been made. The following process parameters are considered: jet tip velocity, jet diameter, target cavity diameter, penetration time and penetration depth (Fig. 1). The jet velocity gradient and jet evolution are carefully analyzed in order to provide evaluation of the position of the virtual origin in time-space coordinates (Fig. 2). Comparison of analytical and numerical model results in terms of the jet tip velocity, penetration velocity and penetration depth has been performed. In contrast to the theoretically constant ratio of penetration velocity to jet tip velocity, the simulation results show that this ratio is actually variable. Analytically determined penetration depth is about 10% higher than numerical evaluation. Generally, an acceptable correlation between analytical and numerical model results has been found, which nevertheless shows that an improvement of analytical models is needed
A HYBRID RELIABILITY - FMEA METHODOLOGY IN RISK ASSESSMENT OF A BELT CONVEYOR SYSTEM
Get PDFAn appropriate maintenance strategy can maximize a machine’s capacity and economic lifetime and also produce yearly savings of several million euros. That being said, a risk assessment approach can help companies identify the systemic bottlenecks that are interfering with their development and cut a large portion of their profit each year. This paper presents a hybrid reliability-Failure Mode and Effects Analysis (FMEA) methodology to assess the risk associated with belt conveyor systems, particularly in open-pit mining environments. By integrating severity, occurrence, and detection indicators, a 3D risk assessment matrix was developed. Using data from conveyor system maintenance, including downtime and failure occurrences, chi-square tests to analyze system reliability and mean downtime were applied. The methodology allows for a nuanced understanding of the frequency and severity of failures, enabling more informed decision-making about maintenance strategies. The paper highlights the economic implications of system failures and the potential for substantial financial savings through optimized maintenance planning