523 research outputs found
Cultural based preconceptions in aesthetic experience of architecture
On a broader scale, the aim of this paper is to examine theoretically the
effects a cultural context has on the aesthetic experience of images existing
in perceived reality. Minimalism in architecture, as direct subject of
research, is a field of particularities in which we observe functioning of
this correlation. Through the experiment with the similarity phenomenon, the
paper follows specific manifestations of general formal principles and
variability of meaning of minimalism in architecture in limited areas of
cultural backgrounds of Serbia and Japan. The goal of the comparative
analysis of the examples presented is to indicate the conditions that may
lead to a possibly different aesthetic experience in two different cultural
contexts. Attribution of different meanings to similar formal visual language
of architecture raises questions concerning the system of values, which
produces these meanings in their cultural and historical perspectives. The
establishment of values can also be affected by preconceptions resulting from
association of perceived similarities. Are the preconceptions in aesthetic
reception of architecture conditionally affected by pragmatic needs, symbolic
archetypes, cultural metaphors based on tradition or ideologically
constructed dogmas? Confronting philosophical postulates of the Western and
Eastern traditions with the transculturality theory of Wolfgang Welsch, the
answers may become more available
Dynamic loads by various water hammer phenomena
Vodeni udar se može pojaviti kako u jednofaznom tako i u dvofaznom strujanju kroz cevovode. Razmatrani su osnovni mehanizmi koji dovode do pojave vodenog udara. Prikazana je i analizirana pojava dinamiÄkih optereÄenja koja su izazvana razliÄitim vrstama vodenih udara. Pokazano je da vodeni udar u dvofaznom sistemu može prouzrokovati mnogo veÄe pikove visokog pritiska nego vodeni udar u jednofaznom sistemu.Water hammer phenomena can be induced both in one-phase and two-phase systems during pipelines transients. The basic mechanisms of fluid dynamics that lead to the water hammer are presented. Dynamic loads induced by several water hammer events are presented and analyzed. It is shown that water hammers in two-phase systems can lead to much higher pressure peaks than water hammers in one-phase systems
Simulations of the kettle reboiler shell side thermal-hydraulics with different two-phase flow models
A computational fluid dynamics approach is presented for the simulation and analyses of the kettle reboiler shell side thermal-hydraulics with two different models of two-phase flow ā the mixture and two fluid model. The mixture model is based on solving one momentum equation for two-phase mixture flow and a closure law for the calculation of the slip between gas and liquid phase velocities. In the two fluid modeling approach the momentum balance is formed for each phase, while the gas-liquid interaction due to momentum exchange at the interface surface is predicted with an empirical correlation for the interface friction coefficient. In both approaches the two-phase flow is observed as two inter-penetrating continua. The models are solved for the two-dimensional geometry of the kettle reboiler shell side vertical cross section. The computational fluid dynamics numerical method based on the SIMPLE type algorithm is applied. The results of both liquid and vapor velocity fields and void fraction are presented for each modeling approach. The calculated void fraction distributions are compared with available experimental data. The differences in the modeling approaches and obtained results are discussed. The main finding is that the void fraction distribution and two-phase flow field strongly depends on the modeling of the slip between liquid and gas phase velocity in mixture model or on the interface friction model in two fluid model. The better agreement of the numerically predicted void fraction with the experimental data is obtained with the two fluid model and an interfacial friction model developed for the conditions of two-phase flows in large volumes of kettle reboilers or different designs of steam generators
Simulations of the kettle reboiler shell side thermal-hydraulics with different two-phase flow models
A computational fluid dynamics approach is presented for the simulation and analyses of the kettle reboiler shell side thermal-hydraulics with two different models of two-phase flow ā the mixture and two fluid model. The mixture model is based on solving one momentum equation for two-phase mixture flow and a closure law for the calculation of the slip between gas and liquid phase velocities. In the two fluid modeling approach the momentum balance is formed for each phase, while the gas-liquid interaction due to momentum exchange at the interface surface is predicted with an empirical correlation for the interface friction coefficient. In both approaches the two-phase flow is observed as two inter-penetrating continua. The models are solved for the two-dimensional geometry of the kettle reboiler shell side vertical cross section. The computational fluid dynamics numerical method based on the SIMPLE type algorithm is applied. The results of both liquid and vapor velocity fields and void fraction are presented for each modeling approach. The calculated void fraction distributions are compared with available experimental data. The differences in the modeling approaches and obtained results are discussed. The main finding is that the void fraction distribution and two-phase flow field strongly depends on the modeling of the slip between liquid and gas phase velocity in mixture model or on the interface friction model in two fluid model. The better agreement of the numerically predicted void fraction with the experimental data is obtained with the two fluid model and an interfacial friction model developed for the conditions of two-phase flows in large volumes of kettle reboilers or different designs of steam generators
Reduction of the specific surface area of porous ZnO during sintering
In this paper reduction of the specifice surface area of porous ZnO during sintering was analyzed. ZnO was sintered at temperatures from 673K to 1173K. Reduction of the specific surface area was observed as a function of the temperature and time of sintering. Analysis of sintering kintetics was done by observing reduction of the specific surface area. We used three different models, defined the appropriate parameters, and also the activation energy of sintering using the Arrhenius equation. The LSE metod was applied for determining optimum parameter values
Two-component two-phase critical flow
U radu je predstavljen model dvokomponentnog dvofaznog kritiÄnog strujanja dvofazne meÅ”avine. Model je validiran poreÄenjem raÄunskih rezultata sa vrednostima izmerenim na PUMA eksperimentalnoj instalaciji. Model je zasnovan na jednodimenzionalnom modifikovanom homogenom izentropskom dvofaznom strujanju teÄnosti i gasa. Homogeni model je modifikovan tako Å”to je klizanje izmeÄu faza uzeto u obzir pri odreÄivanju zapreminskog udela gasne faze u dvofaznoj meÅ”avini, Å”to odreÄuje i gustinu dvofazne meÅ”avine. Klizanje izmeÄu faza je sraÄunato na osnovu Chisholm korelacije koja je pogodna za niže vrednosti masenog protoÄnog udela gasne faze kao i na osnovu Zivi korelacije koja odreÄuje maksimalnu vrednost klizanja izmeÄu faza. Na mestu kritiÄnog isticanja brzina dvofazne meÅ”avine je jednaka brzini zvuka i sraÄunata je na osnovu takozvanog zamrznutog modela dvofaznog strujanja koji ne uzima u obzir fazni prelaz. Ostvareni rezultati su prikazani i uporeÄeni zajedno sa dobro poznatim Fauske modelom dostupnim u literaturi. Pokazano je da Fauske model daje viÅ”e vrednosti kritiÄnog masenog fluksa u odnosu na izmerene vrednosti, dok model prikazan u radu daje prihvatljiva slaganja sa izmerenim podacima.A model of two-component two-phase critical flow is presented. The modelling approach is based on one-dimensional homogeneous gas-liquid two-phase isentropic flow of mixture. The homogeneous model is modified by taking into account the void fraction and two-phase mixture density dependence on velocity slip. The velocity slip is calculated using Chisholm correlation that depends on the gas phase quality and Zivi correlation for the prediction of the maximum velocity slip values. At the location of the critical flow the two-phase mixture velocity equals sonic velocity and it is calculated with the so-called ''frozen sonic velocity' model. The model is validated against data measured in air water flow at the PUMA experimental facility. Obtained results are presented together with the predictions by the well-known Fauske model. It is shown that Fauske model overpredicts measured critical mass fluxes, while the present model shows acceptable agreement with the measured data
Two-component two-phase critical flow
U radu je predstavljen model dvokomponentnog dvofaznog kritiÄnog strujanja dvofazne meÅ”avine. Model je validiran poreÄenjem raÄunskih rezultata sa vrednostima izmerenim na PUMA eksperimentalnoj instalaciji. Model je zasnovan na jednodimenzionalnom modifikovanom homogenom izentropskom dvofaznom strujanju teÄnosti i gasa. Homogeni model je modifikovan tako Å”to je klizanje izmeÄu faza uzeto u obzir pri odreÄivanju zapreminskog udela gasne faze u dvofaznoj meÅ”avini, Å”to odreÄuje i gustinu dvofazne meÅ”avine. Klizanje izmeÄu faza je sraÄunato na osnovu Chisholm korelacije koja je pogodna za niže vrednosti masenog protoÄnog udela gasne faze kao i na osnovu Zivi korelacije koja odreÄuje maksimalnu vrednost klizanja izmeÄu faza. Na mestu kritiÄnog isticanja brzina dvofazne meÅ”avine je jednaka brzini zvuka i sraÄunata je na osnovu takozvanog zamrznutog modela dvofaznog strujanja koji ne uzima u obzir fazni prelaz. Ostvareni rezultati su prikazani i uporeÄeni zajedno sa dobro poznatim Fauske modelom dostupnim u literaturi. Pokazano je da Fauske model daje viÅ”e vrednosti kritiÄnog masenog fluksa u odnosu na izmerene vrednosti, dok model prikazan u radu daje prihvatljiva slaganja sa izmerenim podacima.A model of two-component two-phase critical flow is presented. The modelling approach is based on one-dimensional homogeneous gas-liquid two-phase isentropic flow of mixture. The homogeneous model is modified by taking into account the void fraction and two-phase mixture density dependence on velocity slip. The velocity slip is calculated using Chisholm correlation that depends on the gas phase quality and Zivi correlation for the prediction of the maximum velocity slip values. At the location of the critical flow the two-phase mixture velocity equals sonic velocity and it is calculated with the so-called ''frozen sonic velocity' model. The model is validated against data measured in air water flow at the PUMA experimental facility. Obtained results are presented together with the predictions by the well-known Fauske model. It is shown that Fauske model overpredicts measured critical mass fluxes, while the present model shows acceptable agreement with the measured data
Critical role of electronic correlations in determining crystal structure of transition metal compounds
The choice that a solid system "makes" when adopting a crystal structure
(stable or metastable) is ultimately governed by the interactions between
electrons forming chemical bonds. By analyzing 6 prototypical binary
transition-metal compounds we demonstrate here that the orbitally-selective
strong -electron correlations influence dramatically the behavior of the
energy as a function of the spatial arrangements of the atoms. Remarkably, we
find that the main qualitative features of this complex behavior can be traced
back to simple electrostatics, i.e., to the fact that the strong -electron
correlations influence substantially the charge transfer mechanism, which, in
turn, controls the electrostatic interactions. This result advances our
understanding of the influence of strong correlations on the crystal structure,
opens a new avenue for extending structure prediction methodologies to strongly
correlated materials, and paves the way for predicting and studying
metastability and polymorphism in these systems.Comment: Main text: 8 pages, 4 figures, 1 table; Supplemental material: 2
pages, 1 figure, 2 table
Numerical simulation of condensation induced water hammer
Razvijen je numeriÄki model za simulaciju i analizu hidrauliÄkog udara koji je zasnovan na jednodimenzionalnom homogenom modelu dvofaznog strujanja praÄenju razdelne povrÅ”ine stuba teÄnosti i parnog mehura i modeliranju direktne kondenzacije pare na pothlaÄenoj teÄnosti. Sistem bilansnih jednaÄina je reÅ”en primenom metode karakteristika. Integracija je vrÅ”ena duž tri karakteristiÄna pravca: dva pravca odreÄena su pravcem prostiranja talasa pritiska a treÄi prostiranjem fluidnog deliÄa. PraÄenje fluidnog deliÄa i razdelne povrÅ”ine vode i pare izvrÅ”eno je reÅ”avanjem energetske jednaÄine u prostoru sa taÄnoÅ”Äu treÄeg reda. KoliÄina toplote koju para preda teÄnosti pri kondenzaciji odreÄena je integracijom povrÅ”inskog toplotnog fluksa po razdelnoj povrÅ”ini parne i teÄne faze na mestu kontakta pare i pothlaÄene teÄnosti. Model je primenjen na simulaciju i analizu hidrauliÄkog 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 viÅ”efluidni model za predviÄanje dvofaznog strujanja u vertikalnim cevima. Model je zasnovan na bilansima održanja mase, koliÄine kretanja i energije, koji su primenjeni na svaku fluidnu struju koja je prisutna u posmatranom obliku dvofaznog strujanja, kao i na odgovarajuÄim konstitutivnim korelacijama za odreÄivanje transportnih procesa na razdelnim povrÅ”inama izmeÄu faza. Bilansne jednaÄine za stacionarno stanje su transformisane u oblik pogodan za direktnu primenu numeriÄke metode za integraciju sistema obiÄnih diferencijalnih jednaÄina. Simulirani su termohidrauliÄki procesi duž celog isparivaÄkog kanala, poÄevÅ”i od strujanja i zagrevanja pothlaÄene teÄnosti na ulazu u strujni kanal pa do zasuÅ”enja teÄnog filma i pojave maglenog toka sa kapima ukljuÄenim u gasnu fazu na kraju kanala. TakoÄe, 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
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