Two-component two-phase critical flow

U radu je predstavljen model dvokomponentnog dvofaznog kritičnog strujanja dvofazne mešavine. Model je validiran poređenjem računskih rezultata sa vrednostima izmerenim na PUMA eksperimentalnoj instalaciji. Model je zasnovan na jednodimenzionalnom modifikovanom homogenom izentropskom dvofaznom strujanju tečnosti i gasa. Homogeni model je modifikovan tako što je klizanje između faza uzeto u obzir pri određivanju zapreminskog udela gasne faze u dvofaznoj mešavini, što određuje i gustinu dvofazne mešavine. Klizanje između faza je sračunato na osnovu Chisholm korelacije koja je pogodna za niže vrednosti masenog protočnog udela gasne faze kao i na osnovu Zivi korelacije koja određuje maksimalnu vrednost klizanja između faza. Na mestu kritičnog isticanja brzina dvofazne mešavine je jednaka brzini zvuka i sračunata je na osnovu takozvanog zamrznutog modela dvofaznog strujanja koji ne uzima u obzir fazni prelaz. Ostvareni rezultati su prikazani i upoređeni zajedno sa dobro poznatim Fauske modelom dostupnim u literaturi. Pokazano je da Fauske model daje više vrednosti kritičnog 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 kritičnog strujanja dvofazne mešavine. Model je validiran poređenjem računskih rezultata sa vrednostima izmerenim na PUMA eksperimentalnoj instalaciji. Model je zasnovan na jednodimenzionalnom modifikovanom homogenom izentropskom dvofaznom strujanju tečnosti i gasa. Homogeni model je modifikovan tako što je klizanje između faza uzeto u obzir pri određivanju zapreminskog udela gasne faze u dvofaznoj mešavini, što određuje i gustinu dvofazne mešavine. Klizanje između faza je sračunato na osnovu Chisholm korelacije koja je pogodna za niže vrednosti masenog protočnog udela gasne faze kao i na osnovu Zivi korelacije koja određuje maksimalnu vrednost klizanja između faza. Na mestu kritičnog isticanja brzina dvofazne mešavine je jednaka brzini zvuka i sračunata je na osnovu takozvanog zamrznutog modela dvofaznog strujanja koji ne uzima u obzir fazni prelaz. Ostvareni rezultati su prikazani i upoređeni zajedno sa dobro poznatim Fauske modelom dostupnim u literaturi. Pokazano je da Fauske model daje više vrednosti kritičnog 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

SUSTAINABLE MANAGEMENT OF THE ENERGY RESOURCES OF SERBIA

Energetics has been and remained the key factor of economic changes and economic development to date. If the energy sector is stable, modern, and organized in a quality manner, it also implies welfare for the economy as a whole. Changes in the significance and use of energy in the economy require the professional management of energy development. Irrespective of modern technology and the key discoveries in energy transformation and concentration, it has not declined in significance. On the contrary, energy is the basis of the human activity. On the other hand, the present structure of the primary sources of energy at the global level cannot follow the trend of increasing demand for energy. The limited reserves of the non-renewable sources of energy, especially of crude oil, require our turning towards the renewable sources of energy. The energy crisis of today is not only an expression of the bad condition of natural sources, but a consequence of the global policy for the exploitation of the existing sources of energy. The current condition of energy resources is a consequence of a monopolistic policy for big business and the New World Order founded on it. According to the assessments of the International Energy Agency (IEA), a further increase in primary energy consumption is expected in the period to come. Because of that, it is necessary to strategically plan the development of the energy sector both from the general developmental, technological-economic, and social-ecological points of view. The fact that Serbia has a relatively high energy consumption growth rate, that it is poorer in primary energy reserves in comparison with the world average, refers us yet more to the rational use of the existing reserves of energy and also to the production of energy from renewable sources: solar, the energy of the wind, geothermal, biomass, the energy of the tide and the waves of seas and oceans, and so on. The paper addresses the issues in the field of the sustainable development of energetics, safety and energy efficiency, as well as a future development of energetics in Serbia based on the renewable sources of energy. The economic effects of the production of energy from renewable sources have also been analyzed

Models of regression of the scope of sown areas and purchase prices of oil crops in Serbia

This paper examines the interdependency between the movements of the level of market (purchase) prices and sowed areas under sunflower, soya, and oilseed rape, i.e. between the relative prices of these oil crops and predominant crop-husbandry products (wheat and/or corn), on the one hand, and the areas to be allocated for oil crops cultures. The models of the regression of the scope of sowed areas and purchase prices of oil crops, i.e. the interdependency of these phenomena, are determined by means of reliable statistical methods (the standard error of regression, the coefficient of the trend variation and the determination coefficient). At the same time, the testing of the series has been carried out by means of the mathematical models of functions, whereas the significance of the generated regression dependencies has been estimated by means of the t-test

Influence of the type of cytoplasmic male sterility and restorer genes on grain yield and agronomic traits of maize inbred lines

U ovom radu analizirano je sedam inbred linija kukuruza razlilčitog porekla i dužine vegetacionog perioda. Svaka linija je bila ispitivana u pet varijanti: originalna linija (N), CMS-C, RfC, CMS-S i RfS. Cilj rada je bio upoređivanje agronomskih karakteristika originalnih inbredovanih linija i njihovih CMS i Rf varijanti. Na osnovu poređenja između C i S-tipa linija cilj je bio da se utvrdi koji je od ta dva tipa sterilnosti pogodniji za semensku proizvodnju kukuruza. Nakon dve eksperimentalne godine utvrđeno je da su svih sedam inbred linija pokazale zadovoljavajući stepen sterilnosti. Ni kod jednog tipa (C i S) nije došlo do probijanja sterilnosti (late break of sterility). Sterilne linije su dale viši prinos od svojih analoga. C-tip sterilnosti se pokazao kao nešto bolji za semensku proizvodnju jer je prinos zrna bio veći u poređenju sa S-tipom. Takođe se može reći da je poređenjem ova dva tipa sterilnosti ustanovljeno da je C-tip bio bolji od S-tipa za veći broj ispitivanih agronomskih osobina. Na osnovu fitopatoloških analiza konstatovano je da je S-tip tolerantniji na gljivu Fusarium verticillioides, dok za linije C-tipa se može reći da su otpornije na napad gljive Aspergilus flavus. Parametri stabilnosti po Eberhartu i Rassellu govore da je na osnovu srednjih vrednosti kvadratnog odstupanja od regresije za prinos zrna, S-tip nešto stabilniji od C-tipa u različitim uslovima spoljnjašnje sredine Upotrebom izoelektričnog fokusiranja ustanovljeno je da je prevođenje skoro svih inbred linija urađeno dobro i do kraja. Razlike između originalnih i prevedenih linija su se javile samo kod sledećih linija ZPL2 RfC i ZPL5 RfC. Iz toga se može zaključiti da su razlike u agronomskim osobinama između originalnih i pervedenih linija nastale usled plejotropnog efekta CMS i/ili Rf gena, ili usled njihove interakcije sa spoljašnjom sredinom.Seven maize inbred lines of different origin and different FAO maturity groups were analysed in the present study. Each inbred line was observed in five variants: original inbred (N), CMS-C, RfC, CMS-S and RfS. The objective of the study was to compare agronomic traits of original inbreds and their CMS and Rf variants. The C- and S-type inbreds were compared with the idea to evaluate which of these two types of sterility were more appropriate for seed production. The two-year experimental results show that all seven maize inbred lines had satisfactory level of sterility. None of the type (C and S) showed the late break of sterility. The grain yield was higher in sterile inbreds than in their counterparts. C-type sterility was a bit more appropriate for seed production because grain yield was higher in comparison with the S-type. Furthermore, it can be underlined that the comparison of these two types of sterility showed that the C-type was better than S-type for the majority of observed agronomic traits. According to phytopathological analyses, S-type inbreds are more tolerant to the fungus Fusarium verticillioides, while C-type inbreds are more resistant to the fungus Aspergilus flavus. Based on stability parameters after Eberhart and Russell, i.e. on the mean squared deviation from regression for grain yield, the S-type is somewhat more stable than the C-type under various environmental conditions. Performed isoelectric focusing showed that conversion of all inbreds lines had been done well and completely. The differences between original and conversed inbreds were detected only in inbreds ZPL2 RfC and ZPL5 RfC. Hence, it can be concluded that the differences in agronomic traits between original and conversed inbreds occurred due to pleiotropic effects of CMS and/or Rf gene, or due their interaction with the environment

Odabir ideja u razvoju proizvoda

Unapređenje procesa razvoja proizvoda novim načinom opisivanja, vrednovanja i odabira ideja koje se ugrađuju u koncept novog proizvoda predmet je istraživanja prikazanog u disertaciji. Prikaz aktualnog stanja u području istraživanja dan je iz tri aspekta: razvoja proizvoda, životnog ciklusa ideja, te vrednovanja i odabira ideja. Sustavnim pregledom recentne literature dat je teorijski prikaz područja istraživanja posebno s obzirom na proces razvoja proizvoda, mogućnosti opisivanja, procjene i usporedbe ideja, definiranja atributa za kvalitativno i kvantitativno vrednovanje ideja te metoda za potporu odlučivanju u procesu odabira ideja. Prikaz stanja na području upravljanja idejama u gospodarstvu predočen je rezultatima ankete koja je obuhvatila tvrtke koje u proizvodnom programu imaju strojarske proizvode s vlastitim razvojem. Obradom prikupljenih podataka ustanovljeno je kako i kada se prikupljaju ideje, koji motivi i potrebe su pokretači za prikupljanje ideja, kako su tvrtke organizirane i osposobljene te kako provode procjenu, vrednovanje i odabir ideja. Sastavni dio ankete bilo je i vrednovanje atributa i kriterija za procjenu vrijednosti ideja od strane anketiranih subjekata. Proizašla saznanja iskorištena su za detaljno opisivanje modela podataka za prikupljanje, opisivanje te kvalitativno i kvantitativno vrednovanje ideja. Provedena istraživanja ukazala su na atribute za opisivanje ideja, kriterije za procjenu i metode za vrednovanje i odabir ideja, što je u konačnici rezultiralo prijedlogom metodologije vrednovanja ideja i metodologije odabira ideja za potrebe razvoja proizvoda. U postupku verifikacije, na dva primjera ocijenjena je primjenjivost predloženih metodologija. Pri tome je korišten veći broj procjenitelja a uspoređivani su i korelirani rezultati dobiveni primjenom dviju različitih metoda. Disertacija završava osvrtom na provedeno istraživanje i postignute rezultate sukladno postavljenim ciljevima. Prezentirani su rezultati postignuti istraživanjem zajedno s teorijskim implikacijama na područje razvoja proizvoda. Istaknuti su doprinosi znanju o razvoju proizvoda, te sugestije i pravci za naredna istraživanja

Regionalna obeležja tržišne proizvodnje šećerne repe i suncokreta u Srbiji

The paper analyzes the trends in the development of industrial crop production in the case of sugar beet and sunflower in Serbia from 1976 to 2013. Grouping of regions (4 regions without Autonomous Province of Kosovo and Metohija) and districts (25 districts) in Serbia in 2013, according to the characteristics of land capacity, production of sugar beet and sunflower and level of development, was carried out by cluster analysis. Based on the median value of the important characteristics of available land capacity, production volume and economic development in municipalities, I-distance method were ranked districts in Serbia from 1 to 25. Similarities between the sugar beet and sunflower production regions in Serbia were determined by the method of complete-linkage clustering, and the results were presented in the dendrogram. According to data for 2013 it was found that 99.8% of sugar beet production and 93.9% of sunflower production in Serbia comes from the Vojvodina region. The average yields per hectare for analyzed crops in the areas of the Vojvodina region, on average, were by up to 10% higher compared to the yields in Serbia. According to the characteristics of land capacity and production, areas of the Vojvodina region belong to the highest rank 1-7, while according to the characteristics of the development level, these areas belong to rank 2-13.U radu su analizirane tendencije u razvoju proizvodnje industrijskog bilja, na primeru šećerne repe i suncokreta u Srbiji od 1976. do 2013. godine. Grupisanje regiona (4 regiona, bez KiM) i oblasti (25 oblasti) u Srbiji za 2013. godinu, prema obeležjima zemljišnih kapaciteta, proizvodnje šećerne repe i suncokreta i nivoa razvijenosti, izvršeno je primenom klaster analize. Na osnovu medijalne vrednosti važnijih obeležja raspoloživih zemljišnih kapaciteta, obima proizvodnje i privredne razvijenosti po opštinama, metodom I-odstojanja izvršeno je rangiranje oblasti u Srbiji od 1-25. Sličnosti oblasti proizvodnje šećerne repe i suncokreta u Srbiji predstavljene su metodom kompletnog povezivanja hijarhijske klaster analize, a rezultati su predstavljeni dendrogramom. Prema podacima za 2013. godinu, utvrđeno je da 99,8% proizvodnje šećerne repe i 93,9% proizvodnje suncokreta Srbije potiče iz Regiona Vojvidine. Prosečni prinosi po ha analiziranih biljnih kultura u oblastima Regiona Vojvodine u proseku su veći do 10% u odnosu na prinose u Srbiji. Prema obeležijima zemljišnih kapaciteta i proizvodnje, oblasti Regiona Vojvodine pripadaju najvišem rangu 1-7, dok prema obeležijima nivoa razvijenosti ove oblasti pripadaju rangu 2-13

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

Agrarni potencijali u reindustrijalizaciji Srbije - potrebe i mogućnosti revitalizacije industrije agrarnih inputa

After transitional debacles and failures, structural degradation and recession, reindustrialization is imposed as a crucial stage in the economic development of Serbia. The production-market potentials of the agro-complex (as a complex economic subsystem of pre-farm, farm and post-farm activities) and its place in the national economy open the significant possibilities of the revitalization of the industries of agrarian inputs (agricultural machines and equipment, mineral fertilizers and pesticides). Considering the structural significance of the pre-farm agrarian sector in the Serbian economy, this paper analyzes the fundamental features of production and the foreign-trade exchange, especially the dynamics and changes in the volume and structure of production and the import of agrarian inputs. On that basis, through a target comparative analysis of multi-year data series (1986-2011), the paper explores the trends of production and employment, identifies transitional distortions and the growing import dependence of the Serbian economy and the agro-complex in particular, considers the agrarian potentials in a possible reindustrialization primarily via the revitalization of the industry of agrarian inputs, and highlights a special phenomenon of the opportunity costs of the Serbian agrarian development.Nakon tranzicionih neuspeha i promašaja, strukturne degradacije i recesije, reindustrijalizacija se nameće kao nužna etapa u privrednom razvoju Srbije. Proizvodno- tržišni potencijali agrokompleksa (kao složenog privrednog subsistema predfarmskih, farmskih i postfarmskih delatnosti) i njegovo mesto u nacionalnoj ekonomiji, otvara značajne mogućnosti revitalizacije industrija agrarnih inputa (poljoprivrednih mašina i opreme, mineralnih đubriva i pesticida). Sagledavajući strukturni značajpredfarmskog agrarnog sektora u srpskoj ekonomiji, u radu se analiziraju osnovna obeležja proizvodnje i spoljnotrgovinske razmene, posebno dinamika ipromene obima i strukture proizvodnje i uvoza agrarnih inputa. Na toj osnovi se, ciljnom komparativnom analizom višegodišnjih serija podataka (1986-2011), u radu se istražuju trendovi proizvodnje i zaposlenosti, identifikuje uvozna zavisnost, sagledavaju agrarni potencijali u mogućoj reindustrijalizaciji i ukazuje na poseban fenomen oportunitetnih troškova agrarnog razvoja Srbije