Electrochemical Activity of Thin-Film Pd Catalysts Modified with Bi for Methanol and Ethanol Oxidation Reaction in Alkaline Solution

Thin-film Pd catalysts with low metal loadings (55 and 110 µg cm-2) were obtained by electrodeposition from a surfactant-free green electrolyte on glassy carbon (GC) electrode. Pd/GC catalysts were modified by addition of various amounts of Bi via irreversible adsorption. The catalysts were characterized by atomic force microscopy (AFM) and then studied in methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) in alkaline solution.Electrochemical tests shown that the modification of the appropriate amount of Bi on Pd/GC catalyst enhance activity toward MOR and EOR up to about 2-3 times compared to unmodified catalysts. Besides surface Bi coverage (ƟBi) of 0.6 increase durability and provides more poisoning tolerant Pd/GC electrode in both studied reactions. The improvement of electrochemical performances of Bi modified Pd/GC catalysts is attributed to the third body effect and the bifunctional mechanism

Impact of the parameters of passive solar design and active solar systems on energy use in office buildings

Recent recast of the EU Energy Performance of Buildings Directive, requesting all new buildings in the EU to consume `nearly zero' energy after 2020, requires the coherent application of passive and active design strategies in reducing heating, cooling and lighting loads and utilization of renewable energy. A necessary step in this process is application of the optimal combination of passive design measures, foremost among them being passive solar design measures, which aim to use the solar energy as much as possible in establishing thermal comfort in buildings, without the use of electrical or mechanical equipment. Although it is relatively simple to reduce the energy use up to some extent by applying individual measures, very high levels of energy performance require application of the optimal combination of several different measures. Building energy simulation plays a fundamental role in this process, since the energy use depends in a complex way not only on applied passive solar design strategies, but also on local climate factors. Purpose of this work is to study relationships between the parameters of passive solar design and the heating, cooling and lighting energy loads in office buildings, through a parametric study of a model of an office building located in Belgrade. The case study is a four-story office building, rectangular in shape, with longer sides facing south and north, with windows present at southern and northern facades only. The design parameters include six types of southern glazing types and of northern glazing types, seven values of windows-to-wall ratio for southern and for northern windows ranging from 25% (in order to satisfy minimal daylighting regulations) to 100%, presence of external shading at southern windows, as well as three U-values of external walls. In total, 10,584 building variants have been simulated in EnergyPlus. Analysis of simulation results leads to findings on the optimal windows-to-wall ratio and the optimal glazing choice for southern and northern facade, as well as on the influence of external shading on lowering cooling energy load. Additional simulations of a photovoltaic plant installation on the building model show that a significant number of building variants may became positive energy building with an integration of the photovoltaic plant in the roof of the building

Theologico-Ecclesiological Analysis of the Term ‘Church Music’ in the Light of Anthropological Understanding of Music

Vekovima unazad Pravoslavnom Crkvom odzvanja pojam crkvene muzike. O pozitivnoj recepciji ove sintagme u životu Srpske pravoslavne Crkve svedoči činjenica da se njome često imenuje čitav niz podjednako muzičkih koncepta kao što su: „crkveno pojanje”, „pevničko pojanje”, „višeglasno pevanje (ili notno pjenije)”, „srpsko narodno pojanje”, „karlovačko pojanje”, „beogradsko pojanje” ili pak, „vizantijsko pojanje”. Oslanjajući se na antropološka istraživanja, definiciju muzike izvodimo iz dva međusobno zavisna pristupa. Muzika je kulturni konstrukt koji ne poseduje jedinstvenost i univerzalnost, već brojnost i raznovrsnost značenja koja zavise od kolektivnih i individualnih poimanja; istovremeno, muzika je kulturni fenomen kojim se kreiraju različiti tipovi identiteta počev od etničkog, rodnog, individualnog, kolektivnog, pa sve do lokalnog ili globalnog. Sa stanovišta evharistijskog bogoslovlјa Crkvu predstavlјamo kao Tajnu jedinstva stvorenog i nestvorenog, utemelјenu u Svetotrojičnom načinu postojanja. Identitet Crkve ne smeštamo u istorijske i institucionalne okvire, već ga pronalazimo u eshatologiji – Carstvu Božjem. Evharistijsko pojanje Crkve prikazujemo u klјuču crkvene muzike i njene veze sa antropološkim shvatanjem muzike, a potom analiziramo dobijene rezultate iz ugla pravoslavne eklisiologije. U radu želimo ispitati da li se poistovećivanje evharistijskog pojanja Crkve sa muzikom, kao ljudskom kategorijom, može pozitivno argumentovati u pravoslavnoj teologiji.Throughout centuries, the concept of church music has held significant importance within the Orthodox Church. Its positive reception in the life of the Serbian Orthodox Church is evident by its frequent usage to describe various musical practices, such as: ‘church singing, ‘choral singing, ‘polyphonic singing (or singing from sheet music)’, ‘Serbian folk singing’, ‘Karlovac chant’, ‘Belgrade chant’ or ‘Byzantine chant’. Drawing from anthropological research, we establish the definition of music through two interdependent approaches. Music is a cultural construct that lacks uniqueness and universality, but rather possesses a multitude of meanings dependent on collective and individual perspectives. Simultaneously, music is a cultural phenomenon that engenders diverse forms of identity, ranging from ethnic, gender, individual, collective, to local or global identities. From the perspective of Eucharistic theology, the Church is presented as the Mystery of unity between the created and the uncreated, founded in the Trinitarian nature of existence. The identity of the Church is not confined to historical and institutional frameworks, but is found in eschatology – the Kingdom of God. The Eucharistic church singing is examined in relation to church music and its connection with the anthropological understanding of music. The findings are analyzed from the standpoint of Orthodox ecclesiology. This paper aims to explore whether the identification of Eucharistic church singing with music, as a human category, can be positively argued within Orthodox theology

Searching for regular, triangle-distinct graphs

The triangle-degree of a vertex v of a simple graph G is the number of triangles in G that contain v. A simple graph is triangle-distinct if all its vertices have distinct triangle-degrees. Berikkyzy et al. [Discrete Math. 347 (2024) 113695] recently asked whether there exists a regular graph that is triangle-distinct. Here we showcase the examples of regular, triangle-distinct graphs with orders between 21 and 27, and report on the methodology used to find them.Comment: 7 pages + 11 pages appendix with examples of regular, triangle-distinct graph

Numerical simulation of condensation induced water hammer

Razvijen je numerički model za simulaciju i analizu hidrauličkog udara koji je zasnovan na jednodimenzionalnom homogenom modelu dvofaznog strujanja praćenju razdelne površine stuba tečnosti i parnog mehura i modeliranju direktne kondenzacije pare na pothlađenoj tečnosti. Sistem bilansnih jednačina je rešen primenom metode karakteristika. Integracija je vršena duž tri karakteristična pravca: dva pravca određena su pravcem prostiranja talasa pritiska a treći prostiranjem fluidnog delića. Praćenje fluidnog delića i razdelne površine vode i pare izvršeno je rešavanjem energetske jednačine u prostoru sa tačnošću trećeg reda. Količina toplote koju para preda tečnosti pri kondenzaciji određena je integracijom površinskog toplotnog fluksa po razdelnoj površini parne i tečne faze na mestu kontakta pare i pothlađene tečnosti. Model je primenjen na simulaciju i analizu hidrauličkog udara izazvanog u nekoliko eksperimentalih aparatura.A numerical model for the simulation and analysis of the water hammer in the pipe two-phase flow is developed. The modeling is based on one-dimensional homogeneous model of two-phase flow, tracking of the interface between steam volume and water column and modeling of the direct condensation of steam on sub cooled liquid. The mass, momentum and energy conservation equations are solved by the method of characteristics. For these three equations, there are three characteristic directions: two of them are determined by the pressure wave propagation and the third one by the fluid particle propagation. The fluid particle and the steam-water interface tracking are obtained through the energy conservation equation solving in space, with the accuracy of the third degree. The value of thermodynamic quality is used to determine whether the observed computational region is filled with water, two-phase mixture or steam. The term in the energy conservation equation, which contains information about the heat exchanged between steam and liquid phase through condensation, is determined by integration of superficial heat flux over steam-water interface. The model is applied to the simulation and analysis of the air-water interface propagation in the experimental apparatus of oscillating manometer and the condensation induced water hammer in a vertical pipe for draining of steam into the pool filled with sub cooled water

Multi-fluid model predictions of gas-liquid two-phase flows in vertical tubes

Razvijen je potpun, stabilan, jednodimenzioni višefluidni model za predviđanje dvofaznog strujanja u vertikalnim cevima. Model je zasnovan na bilansima održanja mase, količine kretanja i energije, koji su primenjeni na svaku fluidnu struju koja je prisutna u posmatranom obliku dvofaznog strujanja, kao i na odgovarajućim konstitutivnim korelacijama za određivanje transportnih procesa na razdelnim površinama između faza. Bilansne jednačine za stacionarno stanje su transformisane u oblik pogodan za direktnu primenu numeričke metode za integraciju sistema običnih diferencijalnih jednačina. Simulirani su termohidraulički procesi duž celog isparivačkog kanala, počevši od strujanja i zagrevanja pothlađene tečnosti na ulazu u strujni kanal pa do zasušenja tečnog filma i pojave maglenog toka sa kapima uključenim u gasnu fazu na kraju kanala. Takođe, model je testiran i za uslove nekoliko parcijalnih efekata dvofaznog strujanja.A consistent one-dimensional multi-fluid model is developed for the prediction of two-phase flows in vertical pipes. The model is based on the mass, momentum and energy balance equations for every fluid stream involved in the observed two-phase flow pattern, and corresponding closure laws for interface transfer processes. The steady-state balance equations are transformed in a form suitable for a direct application of the numerical integration method for the system of ordinary differential equations. Thermal-hydraulic processes along the whole length of the boiling channel are simulated, from the flow and heating of sub cooled liquid at the flow channel inlet, and up to the liquid film dry out and gas entrained droplets mist flow at the outlet. Also, the model is tested against several partial effects of two-phase flow

Numerical simulation of condensation induced water hammer

Razvijen je numerički model za simulaciju i analizu hidrauličkog udara koji je zasnovan na jednodimenzionalnom homogenom modelu dvofaznog strujanja praćenju razdelne površine stuba tečnosti i parnog mehura i modeliranju direktne kondenzacije pare na pothlađenoj tečnosti. Sistem bilansnih jednačina je rešen primenom metode karakteristika. Integracija je vršena duž tri karakteristična pravca: dva pravca određena su pravcem prostiranja talasa pritiska a treći prostiranjem fluidnog delića. Praćenje fluidnog delića i razdelne površine vode i pare izvršeno je rešavanjem energetske jednačine u prostoru sa tačnošću trećeg reda. Količina toplote koju para preda tečnosti pri kondenzaciji određena je integracijom površinskog toplotnog fluksa po razdelnoj površini parne i tečne faze na mestu kontakta pare i pothlađene tečnosti. Model je primenjen na simulaciju i analizu hidrauličkog udara izazvanog u nekoliko eksperimentalih aparatura.A numerical model for the simulation and analysis of the water hammer in the pipe two-phase flow is developed. The modeling is based on one-dimensional homogeneous model of two-phase flow, tracking of the interface between steam volume and water column and modeling of the direct condensation of steam on sub cooled liquid. The mass, momentum and energy conservation equations are solved by the method of characteristics. For these three equations, there are three characteristic directions: two of them are determined by the pressure wave propagation and the third one by the fluid particle propagation. The fluid particle and the steam-water interface tracking are obtained through the energy conservation equation solving in space, with the accuracy of the third degree. The value of thermodynamic quality is used to determine whether the observed computational region is filled with water, two-phase mixture or steam. The term in the energy conservation equation, which contains information about the heat exchanged between steam and liquid phase through condensation, is determined by integration of superficial heat flux over steam-water interface. The model is applied to the simulation and analysis of the air-water interface propagation in the experimental apparatus of oscillating manometer and the condensation induced water hammer in a vertical pipe for draining of steam into the pool filled with sub cooled water

Multi-fluid model predictions of gas-liquid two-phase flows in vertical tubes

Razvijen je potpun, stabilan, jednodimenzioni višefluidni model za predviđanje dvofaznog strujanja u vertikalnim cevima. Model je zasnovan na bilansima održanja mase, količine kretanja i energije, koji su primenjeni na svaku fluidnu struju koja je prisutna u posmatranom obliku dvofaznog strujanja, kao i na odgovarajućim konstitutivnim korelacijama za određivanje transportnih procesa na razdelnim površinama između faza. Bilansne jednačine za stacionarno stanje su transformisane u oblik pogodan za direktnu primenu numeričke metode za integraciju sistema običnih diferencijalnih jednačina. Simulirani su termohidraulički procesi duž celog isparivačkog kanala, počevši od strujanja i zagrevanja pothlađene tečnosti na ulazu u strujni kanal pa do zasušenja tečnog filma i pojave maglenog toka sa kapima uključenim u gasnu fazu na kraju kanala. Takođe, model je testiran i za uslove nekoliko parcijalnih efekata dvofaznog strujanja.A consistent one-dimensional multi-fluid model is developed for the prediction of two-phase flows in vertical pipes. The model is based on the mass, momentum and energy balance equations for every fluid stream involved in the observed two-phase flow pattern, and corresponding closure laws for interface transfer processes. The steady-state balance equations are transformed in a form suitable for a direct application of the numerical integration method for the system of ordinary differential equations. Thermal-hydraulic processes along the whole length of the boiling channel are simulated, from the flow and heating of sub cooled liquid at the flow channel inlet, and up to the liquid film dry out and gas entrained droplets mist flow at the outlet. Also, the model is tested against several partial effects of two-phase flow

Fluid dynamic forces in the main steam pipeline of thermal power plant upon stop valves closure

A steam turbine trip is followed by a prompt closure of stop valves in front of the turbine and consequently to a pressure rise in the main steam pipeline. This steam hammer transient leads to the generation of intensive fluid dynamic forces that act along the pipeline axis and induce additional dynamic loads on the main steam pipeline. It is a common practice to assume a simultaneous closure of all stop valves in the safety analysis of the main steam pipeline. In the present paper computer simulations and analyses of the fluid dynamic forces are performed for several scenarios that take into account the possibility of delayed closure of the stop valve in front of the turbine. The influence of the failure of the steam by-pass line opening is considered too. The results show that the delay of the stop valve closure increases the maximum intensity of fluid dynamic force in the pipeline segment in front of the stop valve and decreases the intensity of fluid dynamic forces in segments along the pipeline. The failure of the by-pass line to open leads to prolonged steam pressure and fluid dynamic forces oscillation in pipeline segments. The simulations were performed with the in-house computer code based on the method of characteristics for the solving of the hyperbolic system of PDE that represent the mass, momentum and energy balance equations of the 1-D, compressible and transient fluid-flow. The obtained results are a support to safety analyses of thermal power plants under transient conditions

Characterization of carbon fibrous materials obtained from tree wastes

Carbon fibres can be obtained in rather wide variety of structures, compositions and properties, depending on the nature of the organic precursor and conditions of the process applied in their preparation. In order to get a high surface area, physical or/and chemical activation processes of material have usually been employed. A challenge in the field of carbon adsorbents is to produce very specific materials with a given pore size distribution from low cost precursors. In this study we used new type of a precursor for active carbon fibres material –achenes from the Platanus orientalis seeds. We examined the influence of different chemical activating agents on the porous and electrochemical properties of carbon material support. The properties of these fibers were compared with the properties of polysulfone hollow fibers treated on the similar way. These investigations show that the waste such as fibrous seeds is very promising raw material for active carbon fibers production.Belgrade, Serbia, June 6-10, 201