ADVANTAGES AND DISADVANTAGES OF SOLAR ENERGY PRODUCTION AND USE

The energy released through nuclear fusion on the Sun expands into space in the form of electromagnetic radiation. A total of 1.5x109 TWh reaches the surface of the Earth. About 30% of the energy returns into space by reflexion, whereas 70% of the energy is absorbed on the Earth’s surface (1,05x109 TWh). This amount is greater than the total coal and oil reserves taken together. Using solar energy has its specificities. First, the energy of the Sun records great fluctuations during the day and year. Second, there is a great daily, seasonal, yearly and meteorological variability of the Sun’s radiation accompanied by a very low congruence of the production and consumption of the energy of the Sun. Third, there is a low degree of the conversion of the Sun’s energy to electrical energy. The growth of production and an ever-increasing mass use of solar systems, especially so in China, will for sure exert an influence on a reduction in the prices of these systems in the future. Due to its specificity, the surplus of produced solar energy has to immediately be used or stored in the batteries that are still a major cost of the construction of solar systems. It is more frequently the case that the current surplus of produced solar energy is delivered to electrical power enterprises “to be stored”, whereas the same is taken from the electrical grid during the time of a deficit

Regionalna obeležja tržišne proizvodnje voća i grožđa u Srbiji

In the paper analyzes the trends in the development of market production of fruit (on the example of the apple and the plum) and grapes in Serbia from 1976 to 2015. The grouping of the Serbian districts according to the degree of the market production of fruit and grapes in 2015 was performed by a cluster analysis, on the basis of the six features of production, five features of the capacities, and five features of development. According to the data for 2015, the degree of the marketability of apples in Serbia was 47.7%, plums 15.9%, and grapes 18.3%. The Serbia-North Region shows a surplus in the production of apples, and a deficit in the production of plums (-181.7%) and grapes (-99.1%). The Serbia-South Region has a surplus in the production of the analyzed kinds of fruit (the apple accounting for 43.0%, and the plum 50.9%) and grapes (45.2%).U radu je analizriana regionalna obeležja tržišne proizvodnje voća (na primeru jabuke i šljive) i grožđa po oblastima Srbije u periodu 1976-2015. godine. Grupisanje oblasti u Srbiji prema stepenu tržišne proizvodnje voća i grožđa u 2015. godini izvršeno je klaster analizom na osnovu 6 obeležja proizvodnje, 5 obeležja kapaciteta i 5 obeležja razvijenosti. Prema podacima za 2015. godinu, stepen tržišnosti jabuka u Srbiji iznosio je 47.7%, šljiva 15.9% i grožđa 18.3%. Region Srbija-Sever suficitaran je u proizvodnji jabuka, a deficitaran u proizvodnji šljiva (-181.7%) i grožđa (-99.1%). Region Srbija-Jug suficitaran je u proizvodnji analiziranih vrsta voća (jabuka 43.0% i šljiva 50.9%) i grožđa (45.2%)

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 – 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

Myth about immortality in the contemporary pop culture: A case study about Toše Proeski

This paper explores the intersection of death and ideology in the sphere of popular culture, as exemplified by the afterlife destiny of Toše Proeski, a Macedonian pop singer whose huge popularity continued even after his death. His sudden, untimely death in his twenties had exploded as huge news, preoccupying all sorts of media. What I am interested in this paper is what has happened afterwards. In which way his popularity and his afterlife continue? Can we identify some kind of pop hero cult here, and is it possible to recognize common elements, or even a pattern according to which (newborn) stars develop an afterlife destiny? Can we use this opportunity to discuss immortality myths? Do pop stars get monuments or are these reserved just for national heroes

Large sets of long distance equienergetic graphs

Distance energy of a graph is a recent energy-type invariant, defined as the absolute deviation of the eigenvalues of the distance matrix of the graph. Two graphs of the same order are said to be distance equienergetic if they have equal distance energy, while they have distinct spectra of their distance matrices. Examples of pairs of distance equienergetic graphs appear in the literature already, but most of them have diameter two only. We describe here the distance spectrum of a special composition of regular graphs, and, as an application, we show that for any ▫$n ge 3$▫, there exists a set of ▫$n + 1$▫ distance equienergetic graphs which have order ▫$6n$▫ and diameter ▫$n - 1$▫ each

Finansijsko strukturne promene privrede Srbije i zaštita poverilaca u periodu finansijske krize

Ukorenjena finansijska neravnoteža je opšta karakteristika srpske privrede. Strukturna neuravnoteženost sredstava i njihovih izvora finansiranja praćena kontinuiranim kumuliranjem gubitaka, pogoršanjem likvidnosti i povećanjem zaduženosti oslikavaju finansijski položaj privrede u celini. Cilj rada je analiza finansijske strukture srpske privrede, uz poseban osvrt na identifikovanje privrednih segmenata u kojima su interesi poverilaca ugroženi. Narušena finansijska sigurnost se ogleda i u negativnom neto obrtnom kapitalu, tako da su stanje i razvoj finansijske strukture tokom petogodišnjeg perioda analizirani pomoću neto obrtnog kapitala. Dugogodišnje odlaganje rešavanja problema preduzeća sa izrazitom finansijskom neravnotežom, neodgovarajući zakonski okviri i neadekvatna primena zakona, osim što narušavaju finansijsku strukturu privrede u celini, ugrožavaju interese vlasnika kapitala i poverilaca pojedinih grupa preduzeća. Stoga su u posebnom delu rada analizirani faktori i segmenti preduzeća koji kvare sliku finansijske strukture srpske privrede

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 – 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