Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Proizvodnja biogasa
No full textУ циљу смањења зависности од фосилних горива и иско-
ришћења органских отпадних материјала значајно се развила индустрија
производње биогаса. Биогас је гориви гас који се добија разградњом ор-
ганских материја у анаеробним условима, при чему његов састав и својства
зависе од врсте сировине и избора одговарајућих процесних услова. Рела-
тивно је једноставан за складиштење, има високу топлотну моћ, и веома
је прихватљив као гориво са аспекта емисије гасова који изазивају ефекат
стаклене баште. У раду ће бити посебно обрађени: најважнији прописи и
стандарди из ове области, идентификација расположивости отпадних мате-
ријала и отпадне биомасе за производњу биогаса, својства биогаса, техничке
и технолошке карактеристике постројења за анаеробну обраду отпадних ма-
теријала, конструкционе карактеристике и техничка решења за производњу
биогаса. Такође, биће приказана и примена биогаса, могућности коришћења
отпадног муља из процеса производње биогаса, потенцијал за производњу
напредних биогорива и проблеми у одређивању потенцијала и могућности
коришћења биогаса у Републици Срби
VIŠESTEPENO DOVOĐENJE VAZDUHA PO VISINI LOŽIŠTA KAO PRIMARNA MERA REDUKCIJE AZOTNIH OKSIDA
No full textTemu ovog rada predstavlja istraživanje složenih procesa u ložištu parnog kotla koji
funkcioniše sa višestepenim dovođenjem vazduha po visini ložišta, kao glavnom primarnom merom
redukcije azotnih oksida. Ova kompleksna oblast još uvek nije dovoljno istražena, naročito u
domenu uticaja nove šeme sagorevanja na toplotni proces u ložištu i rad parnog kotla u celini.
Prikazanim istraživanjem afirmisan je pristup primene numeričkih proračuna izdvojenog elementa
složenog energetskog sistema čime je omogućeno definisanje glavnih pravaca promena koje su
nastale u ložištu sa novom organizacijom sagorevanja, što je rezultiralo mogućnošću proširenja
normativnih inženjerskih metoda.
Proširenje postojećih projektnih jednodimenzijskih procedura, izvorno namenjenih samo
nadstehiometrijskim uslovima rada, izvršeno je definisanjem glavnih uticajnih parametara na
procese u domenu gde se sagorevanje odvija u uslovima nedostatka kiseonika. Na ovakav način
dopunjena metodologija omogućila je primenu integralnih proračuna koji kao takvi zahtevaju
skromnije računarske kapacitete i neuporedivo manji utrošak vremena uz značajno suženje
prostora za računsku grešku. Potvrdom rezultata proračuna sa radnim parametrima na realnim
termoenergetskim postrojenjima stvoreni su uslovi za proširenje oblasti primene jednodimenzijskih
modela. Ovim je ujedno i sačuvano, u oblasti primenjenih inženjerskih metoda, akumulirano
iskustvo u projektovanju i praćenju rada energetskih parnih kotlova.
Jedan od glavnih ciljeva sprovedenog istraživanja je da se ovakva metodologija može primeniti
za ispitivanje mogućnosti produženja radnog veka energetskih postrojenja u Republici Srbiji
koja su u eksploataciji preko 30 godina. Kako bi zadovoljili sve strože ekološke norme koje se
odnose na sadržaj azotnih oksida postojeći sistemi moraju implementirati nove koncepcije sagorevanja.
Ovakve procedure mogu se primeniti i za proveru radnih parametara novih postrojenja, na
način na koji se to danas ne vrši, sa mogućnostima ispitivanja mera za povećanje njihove sigurnosti
i efikasnosti.
Prikazani model primenjen je za procenu radnih uslova energetskih parnih kotlova u Republici
Srbiji, koji rade sa novim šemama organizacije sagorevanja primarnim merama redukcije
azotnih oksida. Ovim radom biće prezentovani i rezultati procene rada uzornog energetskog parnog
kotla nakon implementacije nove šeme sagorevanja, za različita opterećenja pri promeni mesta i količine vazduha koja se uvodi po visini njegovog ložišta, a koji predstavljaju osnov za optimizaciju
procesa u celini.ugovor br. 451-03-65/2024-03/200105 i ugovor broj 451-03- 66/2024-03/ 200105 od 5.2.2024
Analiza uzroka havarije na visokopritisnom industrijskom parnom kotlu
No full textPrilikom redovnog rada visokopritisnog industrijskog parnog kotla u hemijsko-industrijskom kompleksu na
teritoriji Republike Srbije došlo je do havarije nakon čega je njegov rad interventno zaustavljen. Neposredno pre
havarije uočen je crni dim na izlazu iz dimnjaka. U toku havarije došlo je do izbijanja zadnjeg zida ložišta kao i
do pucanja dve cevi ozračenog isparivača u njegovoj neposrednoj blizini. Nakon havarije izvršen vizuelni pregled
zatečenog stanja gasnog trakta kao i pratećih elemenata vazdušnog trakta kotla. Za potrebe sprovođenja
analize porekla havarije preuzeti su podaci radnih parametara kotla sa lokalnog DCS sistema za ceo radni dan
u kom se predmetna havarija desila. Analizom svih prikupljenih podataka dato je mišljenje o poreklu havarije
kao i postupci koje je potrebno sprovesti u cilju otklanjanja mogućnosti da se havarija detektovanog porekla
ponovi. Nakon sprovedenih preporuka navedenih u ovom radu očekuje se povećanje pouzdanosti i raspoloživosti
predmetnog kotla kao i povećanje bezbednosti osoblja koje opslužuje kotlovsko postrojenje tokom njegovog rada
BURNING MIXTURES OF NATURAL GAS AND HYDROGEN – CHALLENGES
No full textHydrogen has been strongly proposed as one of the possible solutions to energy
transition lately. On the other hand, it is an accepted fact that fossil fuels will make up at least
50% of primary energy sources after 2050. Natural gas is considered a primary fuel that satisfies
the energy decarbonization concept to a certain level. Knowing the advantages and disadvantages
of natural gas and hydrogen, as gaseous fuels, mixtures of these two gases may appear as an
optimum solution during the energy transition period. This paper deals with the properties of
natural gas and hydrogen that affect the combustion process and burning systems. The effects
on combustion systems performance, are analyzed
COMBUSTION OF LOW CALORIFIC GASEOUS FUELS AS ENERGY- EFFICIENT TECHNOLOGY
No full textThe reserves of fossil fuels will eventually disappear or be reduced to such quantities that they will no longer be able to cover the sectors of final energy consumption (industry, transport, households, trade). For this reason, technologies are constantly being developed to make efficient and effective use of alternative and renewable energy sources, as well as other types of fuels that have potential but require special technologies to be used. In this sense, the combustion of gaseous fuels with a low calorific value, such as gasses produced as a by-product of the anaerobic decomposition of organic material (biogas or landfill gas) or technological gasses produced in certain production processes (blast furnace gas, gas from cupola furnaces, refinery gas, etc.) or gasses from mines, represents a significant potential that can be used as an alternative fuel. Since the middle of the last century, consideration has been given to the development of technologies that allow gasses that are considered waste gasses to be burned efficiently and safely. The disadvantage of gasses produced by various technological processes is the composition's instability and, thus, the variability of heat output. If the heat output of a gaseous fuel is extremely low, this fuel cannot burn stably in burners of classic design, as the flame is then usually "blown off" due to the low combustion rate of this fuel. This article presents the principle of burning gaseous fuels with extremely low heat output in a porous, inert medium. This technology enables efficient heat recovery between the combustion products and the fuel mixture (gaseous fuel + air), significantly extending the range of stable combustion of low calorific value gaseous fuels in various operating modes, which is impossible with classic designburners. This technology is efficient and enables minimal concentrations of components such asnitrogen oxides due to the uniform temperature distribution in the porous inert media of the burner
Excavators’ Cabins Ergonomic Design Influential Factors Modelling: Preliminary Study
No full textExcavator operators encounter demanding work environments with very high risks for discomfort, musculoskeletal disorders, and workplace accidents. In line with that, this study examines the relationship between ergonomic design influential factors using the structural model of excavator cabins design factors, using a sample of 32 excavator operators. Descriptive statistics were performed to describe the operator's age, height, weight, working experience, and excavator's lifespan. After that, the structural equations model was developed to describe the impact of latent variables related to ergonomic design of the cabin. This model was constructed by using 17 questions, which were categorized into 5 groups based on ergonomic design characteristics such as seat, armrests, commands, cabin, and working conditions. The findings indicate that the model exhibits favourable reliability and validity coefficients, a substantial effect size, and a satisfactory model fit. Further research is needed to increase the sample size, despite the preliminary nature of the current research and its satisfactory results
DIMENSIONAL ACCURACY OF SINTERED DENTAL METALWORK: EVALUATING 3D PRINTING PRECISION FROM INTRAORAL SCANS TO FINAL FIT
No full textThe precision of 3D printing in the fabrication of sintered dental metalwork is critical for successful clinical outcomes. However, during the initial trial of these metal components on the patient, a dimensional discrepancy often manifests itself, indicating a poor fit despite being modeled from precise intraoral scans. This necessitates additional corrections or reprinting, thus extending the duration of treatment, increasing costs, and raising concerns about the reliability of 3D printing and subsequent processing techniques. This study aims to quantitatively analyze the dimensional changes in sintered dental metalwork from the original intraoral scan to the final product and to evaluate whether these changes are influenced by the complexity of the metalwork design. Using a 3D scanner (Atos Core 200, GOM, Germany), the dimensions of the sintered metalwork were compared to the corresponding CAD models. Preliminary results indicate significant dimensional deviations, particularly in more complex designs, underscoring the need for improved accuracy in
the 3D printing process to enhance clinical outcomes and efficiency
APPLICATION OF 2D AND 3D DIGITAL IMAGE CORRELATION IN TESTING PRESSURE EQUIPMENT AND RELATED MATERIALS
No full textDigital Image Correlation (DIC) method, including both 2D and 3D DIC, plays an important
role in testing and evaluating pressure equipment integrity, as well as materials used in pressure
equipment. The 2D DIC method, employing a single-camera setup, is particularly suited for
assessing surface deformation and strain distribution in simpler geometries and thin-walled
pressure components under various loading conditions. This technique efficiently identifies
localized strains, surface defects, and initial crack formation, crucial for maintaining the
structural integrity of pressure vessels, piping, and storage tanks. Due to its ease of
implementation, 2D DIC is often applied in laboratory tensile tests, pressure cycle tests, and
validation of finite element models for flat or nearly flat pressure equipment surfaces.
On the other hand, 3D DIC, utilizing a stereo, dual-camera arrangement, significantly expands
the measurement capabilities, allowing accurate assessment of complex, three-dimensional
deformation fields present in curved or intricate geometries typical of pressure equipment. The
method effectively captures out-of-plane displacements and complex strain distributions arising
under internal pressure conditions, thermal loading, and fatigue tests, that are common
operational scenarios for pressure equipment. The advanced spatial measurement capabilities of
3D DIC enable precise identification of critical regions prone to failure, including weld joints,
nozzles, and geometrical discontinuities. Consequently, 3D DIC provides critical insights into
material behavior and structural response, enhancing safety, performance, and reliability in
pressure equipment.
Integrating DIC methodologies with advanced data processing techniques, further improves the
predictive capabilities and accuracy of strain measurements. These advancements facilitate early
damage detection and real-time structural health monitoring, significantly reducing the risk of
unexpected equipment failures. Ultimately, the focused application of 2D and 3D DIC in pressure
equipment testing supports more efficient design optimization, maintenance scheduling, and
regulatory compliance, reinforcing its importance within the domain of structural integrity
assessment
Error bound of Gaussian quadrature rules for certain Gegenbauer weight functions
No full textIn this paper we present an extension of our previous research, focusing on a method to numerically evaluate the error term in the Gaussian quadrature formula with the Legendre weight function, as discussed by Jandrlic et al. (2022). For an analytic integrand, the error term in Gaussian quadrature can be expressed as a contour integral. Consequently, determining the upper bound of the error term involves identifying the maximum value of the modulus of the kernel within the subintegral expression for the error along this contour. In our previous study, we investigated the position of this maximum point on the ellipse for Legendre polynomials. In this paper, we establish sufficient conditions for the maximum of the modulus of the kernel, which we derived analytically, to occur at one of the semi-axes for Gegenbauer polynomials. This result extends to a significantly broader case. We present an effective error estimation that we compare with the actual one. Some numerical results are presented
Analysis of failures of elements of draw gear and impacts on the safety of rail vehicles
No full textRail transportation is one of the most efficient ways of transporting goods and passengers. Alongside modern and reliable infrastructure systems, special emphasis is placed on the reliability, availability, and safety of rail vehicles. The draw gear device plays a pivotal role in ensuring operational safety and efficiency. However, failures within this system can lead to catastrophic consequences, compromising the safety of both passengers and goods. This paper analyzes the root causes and impacts of draw gear failures on rail vehicle safety through a comprehensive analysis of historical data, current data, and simulation of failure by numerical analysis.
The analysis reveals that draw gear failures stem from various factors, including material fatigue, design deficiencies, improper maintenance, and operational conditions. These failures can result in the breakage of elements that can cause derailments, collisions, and other accidents. Such incidents pose significant risks to human life, property, and the environment. Furthermore, the economic implications of such failures, including repair costs, service disruptions, and legal liabilities, underscore the importance of proactive mitigation strategies.
By identifying common failure modes and their underlying mechanisms, this research provides valuable information and data for enhancing the reliability and safety of draw gear systems. Results obtained from these analyses can be used to improve design, material selection and characteristics, maintenance, and monitoring technologies. Additionally, the analyzed data emphasize the importance of industry collaboration in mitigating the risks associated with draw gear failures and ensuring the continued safety and efficiency of rail transportation systems