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ENRICHMENT OF LOW-CALORIE GASEOUS FUELS WITH HYDROGEN
No full textThe quite certain introduction of hydrogen and mixtures of hydrogen and low calorific value gases (bio-gas and land-fill gas) for the energy needs of modern society reveals a number of open questions related to the problems of applying these fuels in future commercial gas devices and systems. Currently, fuel cells are the only commercialized devices for using hydrogen. In the case of using hydrogen by the combustion method, there are already commercialized gas turbines of high power, while in the case of devices of lower power, manufacturers are still in the research and development phase. Serbia is given the opportunity to be in the process of developing the technology for the application of hydrogen in the energy sector.This paper was presented at the Second International Symposium on Risk Analysis and
Safety of Complex Structures and Components (IRAS 2023), 2-4 April 2023, Belgrade, Serbi
Magnesium substitution with nickel and its influence on the sensing properties of MgFe2O4
No full textMixed spinel ferrites MgxNi1-xFe2O4 were synthesized via sol-gel combustion synthesis with citric acid as fuel, followed by calcination at 700 °C for 3 hours. Obtained powders were characterized via X-ray diffraction analysis (XRD), X-ray photoelectron (XPS), FTIR and Raman spectroscopy and FESEM microscopy. Elemental composition was examined via energy dispersive spectroscopy (EDS). Humidity sensing properties were tested by measuring AC impedance in a climactic chamber at 25 °C and in the relative humidity range of 40–90%. Temperature sensing properties were tested by measuring DC resistance at 40% RH in the temperature range 40–90 °C. Synthesized powders were proven to be pure spinel Fd 3m phase with spherical, slightly agglomerated particles. Substitution of Mg with Ni results in structural changes such as a change in inversion parameter and particle agglomeration, which influences sensing properties of the material. Results show that the sensing properties of magnesium ferrite, which is already a well-established NTC sensor, can be improved by incorporating 10% of nickel in the spinel lattice structure. Mg0.9Ni0.1Fe2O4 exhibited higher temperature sensitivity and higher sensitivity towards humidity compared to MgFe2O4, while further substitution of Mg with Ni resulted in the decline of sensing properties, increase in particle size and agglomeration degree
Towards innovative and more efficient solutions for heat exchangers in aerospace industry
No full textHeat exchangers used in the aerospace industry have inherent requirements for maximizing heat transfer efficiency, reducing weight and size, ensuring enhanced durability, and enabling customization for different aircraft types. 3D printing technology allows for the utilization of advanced materials such as high-temperature alloys and ceramics, which can withstand the extreme conditions of aerospace environments. Recent studies have highligheted the potential of 3D-printed heat exchangers in various aerospace industry, including spacecraft thermal management, electronics cooling and aircraft engine cooling.
Heat exchangers modeled on the basis of TPMS (Triple Periodic Minimal Surface) structures exhibit high surface area-to-volume ratios and interconnected pore structures, resulting in significant enhancement in heat
transfer rates. TPMS has been extensively researched in mathematics and materials science for several decades, with classical examples like the Schwartz surface, Gyroid surface and Diamond surface mainly studied for designing small-scale heat exchangers. Numerous studies have demonstrated improved heat transfer efficiency, structural stability and durability of 3D-printed heat exchangers. However, the design of TPMS structures using existing CAD systems poses challenges and further improvements are needed in modeling process.
Overall, the combination of 3D printing technology and geometry optimization represents the state-of-the-art in heat exchanger research, holding significant potential to transform existing systems and drive the development of innovative and more efficient energy systems in the aerospace industry
Influence of plasma transferred arc welding parameters on the obtained microstructure of 316L coating
Get PDFThe paper describes the surfacing technology for coating of high-alloyed austenitic stainless steel 316L on the steel S235JR base material. Coatings were applied by plasma transferred arc welding process. The 5 samples were made using different welding currents while other welding param¬eters were constant. Metallographic analysis of the obtained samples is used to establish a correlation between the micro¬structural constituents and the applied welding current in the surfacing process. According to this it was possible to determine the optimal parameters of coating surfacing. The filler material was in the form of powder, while its charac¬terization was performed by scanning electron microscopy, and the characterization of the obtained coatings by optical microscopy
The development and preliminary validation of the Serbian value lexicon – An archival approach to value measurement
No full textValues refer to stable beliefs and principles held by individuals, which guide their attitudes, behaviours, and judgments, and play a crucial role in shaping their identities and interactions with others. Studying values in social psychology is important as it provides insights into the motivational forces that drive individuals’ behaviour and decision-making, shaping the dynamics of interpersonal relationships and societal interactions. The aim of this paper is to test the possibility of measuring basic values in the archive and text materials. Based on the Schwartz’s theory of values and earlier work on the value lexicon in English, the Serbian lexicon of values was developed and preliminarily validated on a large-scale Internet-based survey. The lexical co-occurrence of words in the natural language use on the Internet was analysed in order to assess the convergent, discriminant and predictive validity of the lexicon. Lexical cooccurrence analysis showed that the words representing the same values cooccurred significantly more in comparison to the words denoting different values. The pattern of correlations between the values measured in the archive material on the Internet using the value lexicon showed high convergence with the pattern of correlations between the values assessed by the self-reported measures used in the European Social Survey in 2018. The relative prominence of the specific values on the official websites of the exemplar societal institutions and organizations identified by the value lexicon was in line with the expectations and preliminarily confirmed the criterion validity of the lexicon of values. Possible applications of the lexicon of values, as well as some methodological issues pertaining to its future use, are discussed in the final part
Time-dependent behaviour of photosensitive resins in mSLA technology
No full textVat photopolymerization is an Additive Manufacturing (AM) technology that enables the production of dimensionally accurate components. Due to its accuracy, this technology has led to the development of various sub-types, each with different methods of introducing UV light to the liquid resin in the vat. UV light can be introduced through a mirror system (SLA), a projector (DLP), or an LCD screen that acts as a photomask over a projector’s light, allowing for the curing of the entire layer in one pass (MSLA). The material of interest in this study is a standard translucent resin used in MSLA, with a UV light wavelength of 405 nm. Previous extensive mechanical characterization of this material has shown a high dependence on the final component properties on layer thickness and curing times.
The objective of this research is to analyse the time-dependent behaviour of these materials. Specifically, closed-loops compression tests have been conducted, subjecting the material to loading and unloading sequences at strain levels of 5 and 25 %. To clarify, a strain level of 5 % falls within the elastic region of the material, while a strain level of 25 % is considerably within the plastic region. Various testing speeds were applied, namely 1, 5, 10, 25, and 100 mm/min. The influence of testing speed on the materials’ energy absorption capacity is evident. The highest difference is observed between 10 and 25 mm/min, indicating that the material’s ability to store energy is significantly reduced after a testing speed of 10 mm/min
Quality managment of protective coating based on zirconium silicate
No full textThe composition and production procedures of refractory coatings based on zirconium silicate for the protection of metal
structures in conditions of wear, cavitation and corrosion were investigated in the paper. The composition of the coating was defined
with a filler based on zirconium silicate, a binder based on epoxy resin, organic additives and an organic solvent. A method for quality
control of obtained coatings was investigated using the ultrasonic vibration method with a stationary sample according to the ASTM
G 32 standard.
The following methods were used to characterize the obtained filler samples: X-ray diffraction analysis (XRD) and scanning electron
microscopy (SEM). The change in the mass of the samples as a function of the cavitation time was monitored and the cavitation rate
was determined. The formation and development of damage to the coating surface was monitored using a scanning electron
microscope. The obtained test results showed a satisfactory resistance of the protective coatings to the effect of cavitation, with small
damage to the coating surface and a cavitation rate of 0.6 mg/min. Tests have shown that the application of the ultrasonic vibration
method is suitable for a quick assessment of the quality of protective coatings during synthesis and a forecast of their resistance and
stability during exploitation in the protection of equipment parts in mining and metallurgy
Information and Query in BIM
No full textMost of today's BIM technologies treat information as a set of structured data. This approach resulted in numerous standards and technologies aimed at the completeness and quality of the information model itself. If we pay attention to the fact that the first papers that formulated the mathematical theory of information inextricably link information with communication, we will see that the party receiving the message represents a key part in the understanding of information. What's more, information does not exist without the receiving party. All information models represent only a source of information, not information. In order to ensure that the end user receives the desired information, it is necessary to find ways to represent the end user needs and define ways to query the BIM model in accordance with them.
Querying IFC file is not an easy task. Parsing directly file format is a problem due to the structure of the STEP file. To overcome these limitations, other representations based on XML, RDF and OWL formats have been developed. Second approach is to use a database management system (DBMS) to access and query information. Since IFC format is full of relationships the graph database is effective solution.
The paper analyzes the existing solutions for the representation of the IFC format through databases and Linked data technologies and determines the ways in which they can be connected with the existing technologies for the representation of information requirements