Numerical simulation of hot water temperature waves propagation in complex networks

U okviru doktorske disertacije je razvijen numeriĉki postupak za proraĉun prostiranja temperaturskih talasa i razdelne površine izmeĊu stuba teĉnosti i parne faze u cevovodima i sloţenim cevnim mreţama. Postupak je zasnovan na rešavanju energijske jednaĉine jednodimenzionalnog strujanja homogenog fluida. Energijska jednaĉina se rešava numeriĉki duţ karakteristiĉnog pravca odreĊenog kretanjem fluidnog delića u vremensko-prostornom koordinatnom sistemu. Postupak numeriĉkog rešavanja je eksplicitan i vremenski korak integracije je odreĊen minimalnim vremenom potrebnim da fluidni delić preĊe rastojanje od poĉetnog poloţaja, koji se u opštem sluĉaju nalazi izmeĊu ĉvorova mreţe, do najbliţeg susednog numeriĉkog ĉvora u pravcu strujanja, u okviru cele mreţe (Courant-ov kriterijum). Primenom Lagrange-ovog interpolacionog polinoma se odreĊuje vrednost temperature ili entalpije u poĉetnom vremenskom trenutku izmeĊu ĉvorova numeriĉke mreţe, na karakteristici koja predstavlja pravac prostiranja fluidnog delića. Razvijene su bilansne jednaĉine koje omogućuju proraĉun graniĉnih uslova, kao što su spoj tri ili više cevi u ĉvoru, toplotnorazmenjivaĉke podstanice kod potrošaĉa i u izvoru toplote. Razvijena metoda je primenjena na simulaciju prelaznog procesa u okviru sistema daljinskog grejanja toplane Zemun nastalog usled promene snage izvora toplote. Razvijeni numeriĉki postupak je primenjen i za simulaciju i analizu hidrauliĉkog udara izazvanog kondenzacijom pare. Neposredni kontakt pothlaĊene teĉnosti i pare u stanju zasićenja dovodi do intenzivne kondenzacije. Brzina kondenzacije zavisi od specifiĉne razdelne površine teĉne i parne faze i koeficijenta prelaza toplote usled kondenzacije. Razdelna površina teĉnosti i pare ima veoma nepravilan oblik. Za vreme hidrauliĉkog udara izazvanog kondenzacijom pare nestacionarni mlazevi teĉnosti i kapi se odvajaju sa ĉela stuba teĉnosti i ukljuĉuju se u zapreminu pare. Ova pojava ukljuĉivanja znaĉajno povećava razdelnu površinu i brzinu kondenzacije. U cilju predviĊanja brzine kondenzacije u ovakvim sloţenim uslovima, razvijena je korelacija izmeĊu ubrzanja ĉela vodenog stuba i proizvoda specifiĉne razdelne površine teĉne i iv parne faze i koeficijenta prelaza toplote pri kondenzaciji...A high-order accurate numerical method for prediction of thermal transients and propagation of interfacial area between liquid column and steam in pipelines and complex pipe network is presented. It is based on the numerical solution of the transient energy equation for one-dimensional homogeneous fluid flow. Transient onedimensional energy balance equation is solved along the characteristic path that is determined by the fluid particle motion in time-space coordinate system. Numerical method of solving is explicit and the time step of the integration is determined by the minimal time needed for fluid particle to cross the distance between the initial point, in general case positioned between two adjacent nodes of numerical mesh, and the closest node in the flow direction, in whole mesh (Courant criterion). The initial value of temperature or enthalpy between nodes of numerical mesh, on characteristic path which represents fluid particle propagation direction, is determined by the application of Lagrange's interpolation polynomial. Balance equations for boundary conditions are developed, e.g. junctions of three or more pipelines, heat exchanger substations at costumers and in heat source. Thermal transients caused by an increase and decrease of the heat power plant load are simulated for real operating conditions of the district heating system Zemun. Developed numerical model is also applied for simulation and analysis of condensation induced water hammer. Direct contact of subcooled liquid and saturated steam leads to intensive condensation. Condensation rate is highly influenced by the interfacial area concentration and condensation heat transfer coefficient. The interfacial area has very irregular shape. During the condensation induced water hammer transient liquid jets are formed and liquid column is dissintegrated so that droplets from the head are entrained in steam volume. This droplet entrainment increases interfacial area and condensation rate. Two-phase system of liquid and steam is described by the mass, momentum and enthalpy conservation equations which form a system of quasi linear partial differential equations of the hyperbolic type. Given system is solved by the vi method of characteristics..

Uticaj BA i BA+GA4+7 na formiranje prevremenih grančica na jednogodišnjim sadnicama sorti jabuke

This study presents the influence of BA (6-benzyladenine) and BA+GA4+7 (6-benzyladenine + gibberellic acids 4 and 7) on feathering of one-year-old apple trees of two cultivars Jonagold and Čadel. Different concentrations of BA (300, 600, 1,200 and 1,800 mg L-1) and BA+GA4+7 (500, 1,000, 1,500 and 2,000 mg L-1) were applied, and two treatments for both chemicals were performed. The first treatment was applied at 70-cm height of nursery trees and the second 2 weeks later. Comparison was performed in relation to untreated control. An application of BA and BA+GA4+7 did not affect both rootstock and nursery tree diameter at 10 cm above the grafting union. Nursery trees of cultivar Jonagold were not influenced by treatments applied, whereas in cultivar Čadel, the treatment with BA+GA4+7 decreased apical growth of nursery trees. The development of sylleptic shoots in both cultivars tested was influenced by the type of growth regulator and concentration applied. Treatment with BA at 300 mg L-1 concentration in both cultivars tested did not influence total length and number of sylleptic shoots, as well as the number of sylleptic shoots longer than 20 cm. The most positive influence on all studied parameters was observed on nursery trees treated with the concentration of 1,200 mg L-1 BA. The lowest concentration of BA+GA4+7 (500 mg L-1) caused the low feathering of both studied cultivars. The higher concentrations (1,000, 1,500 and 2,000 mg L-1) similarly increased the number and total length of sylleptic shoots of nursery trees.U ovom radu je ispitivan uticaj BA (6-benziladenin) i BA+GA4+7 (6-benziladenin + giberelinska kiselina 4 i 7) na bočno grananje jednogodišnjih sadnica dve sorte jabuke Jonagold i Čadel. Primenjene su različite koncentracije BA (300, 600, 1.200 i 1.800 mg L-1) i BA+GA4+7 (500, 1.000, 1.500 i 2.000 mg L-1) pri čemu su kod oba hemijska jedinjenja tretmani izvedeni dva puta. Prvi tretman je izveden kada su sadnice bile visine 70 cm, a drugi tretman je izveden dve nedelje kasnije. Kontrola je bila bez tretiranja. Primena BA i BA+GA4+7 nije ispoljila uticaj na prečnik podloge i sadnice na visini od 10 cm iznad spojnog mesta. Kod sadnica sorte Jonagold nisu registrovane razlike u vršnom porastu pod uticajem primenjenih tretmana, dok je kod sorte Čadel tretman sa BA+GA4+7 uticao na smanjenje vršnog porasta sadnica. Ustanovljeno je da su tip hemijskog regulatora i primenjena koncentracija uticali na razvoj prevremenih grančica kod obe ispitivane sorte. Tretman sa BA u koncentraciji od 300 mg L-1 nije ispoljio uticaj na ukupnu dužinu i broj prevremenih grančica, kao i na broj prevremenih grančica dužih od 20 cm. Najpozitivniji uticaj na sve ispitivane parametre je zabeležen kod sadnica tretiranih sa BA u koncentraciji od 1.200 mg L-1. Najniža koncentracija BA+GA4+7 (500 mg L-1) je izazvala slabo grananje sadnica kod obe ispitivane sorte. Veće koncentracije (1.000, 1.500 i 2.000 mg L-1) su uslovile slično povećanje broja i ukupne dužine prevremenih grančica na sadnicama

Uticaj genotipa i uzrasta na proizvodne osobine lakih linijskih hibrida kokoši

The aim of this work was parallel investigation of the producing characteristics of light line hen hybrids. Investigation enclosed two hen proveniences: Hisex Brown and Shawer 579. Within the period of 19 up to 63 weeks we followed next parameters: egg-laying hen body mass, mortality, food consumption and egg-laying capacity. Hens body mass on the beginning of the examination, within the 19 weeks of growth was, for Hisex Brown provenience 1607g, and for Shawer 579 provenience 1563g. Hisex Brown provenience achieved about 250 g higher body mass on the end of investigation. During the experiment, mortality at Hisex Brown egg-laying hen was a little bit smaller (5,40%), while the Shawer 579 had 5,56% of dead hens. Globally, the mortality at both hen hybrids was in the range of technological normative. The average consumption of the food at Hisex Brown provenience was higher and it was 127,28g, and at Shawer 579 provenience 125,14g. The average consumption of the nutrition for egg production at both provenience was the same (150g).Cilj ovog rada bio je da se izvrši uporedno ispitivanje proizvodnih sposobnosti lakih linijskih hibrida kokoši. Ispitivanjima su obuhvaćene dve provenijence kokoši: Hisex Brown i Shawer 579. U periodu od 19. do 63. nedelje starosti praćeni su sledeći parametri: telesna masa nosilja, mortalitet, utrošak hrane i nosivost. Telesna masa kokoši na početku ispitivanja, sa 19 nedelja uzrasta, za provenijencu Hisex Brown, iznosila je 1607 g, a za provenijencu Shawer 579-1563 g. Veću telesnu masu na kraju eksperimenta, za oko 250 g postigle su nosilje provenijence Hisex Brown. U toku ispitivanja, mortalitet kod Hisex Brown nosilja je bio nešto manji (5,40%), dok je Shawer 579 imao 5,56% uginulih nosilja. Posmatrano u celini, mortalitet nosilja kod oba hibrida, bio je u granicama tehnoloških normativa. Prosečna dnevna potrošnja hrane kod provenijence Hisex Brown je veća i iznosila je 127,28 g, a kod Shawer 579-125,14 g. Prosečna potrošnja hrane za proizvodnju jajeta kod obe provenijence je bila ista (150 g)

Ferromagnetic behaviour of the Zn-Mn-O system

Polycrystalline Zn-Mn-O samples with nominal manganese concentrations x = 0.0 1, 0.04 and 0.10 were synthesized by a solid state reaction route using (ZnC(2)O(4 center dot)2H(2)O)(1-x) and (MnC(2)O(4)-2H(2)O)(x). Thermal treatment of the samples was performed in air at temperatures 673, 773, 873, 973 and 1173 K for x = 0.01 and at the temperature 773 K for x = 0.04 and 0.10. The samples were investigated by X-ray diffraction, thermogravimetry, differential thermal analysis, transmission electron microscopy, magnetization measurements and electron paramagnetic resonance. X-Ray diffraction was also performed on MnO(2) thermally treated at temperatures 673, 773, 873, 973, 1073 and 1173 K. Room temperature ferromagnetism was observed in the Zn-Mn-O samples with x = 0.0 1 thermally treated at low temperatures (673 and 773 K) and in the sample with x = 0.04 thermally treated at 773 K. It seems that the ferromagnetic phase could originate from interactions between Mn(2+) and acceptor defects incorporated in the ZnO crystal lattice during the thermal treatment of the samples

Sodium-alginate biopolymer as a template for the synthesis of nontoxic red emitting Mn2+-doped CdS nanoparticles

Manganese-doped cadmium sulfide (CdS:Mn) nanoparticles were prepared by chemical synthesis using sodium-alginate as template. The preparation of the nanocomposites involved ionic crosslinking of the biopolymer by dimerization of its alpha-L-guluronic monomers with Cd2+ and subsequent formation of the semiconductor nanoparticles upon addition of sulfide ions in the presence of Mn2+. The crystalline phase of CdS in the material was confirmed by XRD. The surface morphology of the nanocomposites was investigated by SEM. The observation by TEM showed that the CdS:Mn particles were spherical in shape with diameters of approximately 4 nm. EPR measurements of the CdS:Mn-alginate nanocomposite showed that the Mn2+ ions were incorporated in cationic sites of CdS with lower symmetry. Due to a distorted crystal field induced by the Mn2+ ions, photoluminescence spectra of the CdS:Mn-alginate showed red fluorescence between 650 nm and 750 nm falling into the optical window for bioimaging in which the light has its maximum tissue penetration depth. It was demonstrated that the interaction between the nanoparticles and the matrix prevents release of CdS into the environment, leading to low acute toxicity of the nanocomposites

Distribution and forms of iron in the vertisols of Serbia

Soil of arable land and meadows from the Ap horizon, taken from ten different localities, were investigated for different forms of Fe, including total (HF), pseudo-total (HNO3), 0.1 M HCl extractable and DTPA (diethylenetriaminepentaacetic acid)-extractable. A sequential fractional procedure was employed to separate the Fe into fractions: water soluble and exchangeable Fe (I), Fe specifically adsorbed with carbonates (II), reducibly releasable Fe in oxides (III), Fe bonded with organic matter (IV) and Fe structurally bonded in silicates (residual fraction) (V). The soil pH, cation exchange capacity, and size fractions (clay and silt) had a strongest influence on the distribution of the different forms of Fe. The different extraction methods showed similar patterns of the Fe content in arable and meadow soils. However, the DTPA iron did not correspond with the total iron, which confirms the widespread incidence of iron-deficiency in vertisols is independent of the total iron in soils. The amount of exchangeable (fraction I) and specifically adsorbed (II) iron showed no dependence on its content in the other fractions, indicating low mobility of iron in vertisols. The strong positive correlation (r = 0.812 and 0.956) between the content of iron in HNO3 and HF and its contents in the primary and secondary minerals (fraction – V) indicate a low content of plant accessible iron in the vertisol. The sequential fractional procedure was confirmed as suitable for accessing the content and availability of iron in the vertisols of Serbia

Room-Temperature Ferromagnetism in Zn-Mn-O, X-Ray Photoemission Surface Study

Room temperature ferromagnetic properties of Zn-Mn-O show evident dependence on manganese concentration and preparation conditions. We systematically studied series of samples with manganese concentration ranging from 0 to 10 at.%, prepared in air at thermal treatment temperatures ranging from 400 to 900 degrees tau C. The samples were investigated by X-ray diffraction, TEM, magnetization measurements and XPS spectroscopy. XPS analyses of surface composition, chemical bonding and XPS depth profiling were successfully employed on powder revealing the chemical composition at the surface of the grains and underneath. The study emphasizes important role of the grain surface in observed room temperature ferromagnetism. It seems that the ferromagnetic phase is correlated with oxygen build up at the surface.12th Annual YUCOMAT Conference, Sep 06-10, 2010, Herceg Novi, Montenegr

EPR analiza Cd1-xMnxS kvantnih tačaka

Cd1-xMnxS kvantne tačke dijametra d ≤ 4.5 nm su dobijene taloženjem vodenog rastvora. Koncentracije mangana u merenim uzorcima su bile od x = 0.001 do x = 0.25. Izvršena su merenja EPR spektara u oblasti temperatura 20-290 K pomoću 9.5 GHz spektrometra. Za sve koncentracije mangana uočeno je da se spektar sastoji od široke linije i hiperfine strukture. Hiperfina struktura je opisana centralnim (MS = 1/2 ↔ MS = -1/2) dozvoljenim i zabranjenim prelazima sa konstantom hiperfine strukture |A| = 9.6 mT i sa parametrom razdvajanja aksijalnog polja D od 11.1 do 13.5 mT. Hiperfina struktura je pripisana izolovanim Mn2+ jonima na površini nanokristala. Širina široke rezonatne linije koja se ne menja sa temperaturom znači da ona potiče od necentralnih manganovih prelaza proširenih efektom kristalnog polja, kao i u nekim neuređenim materijalimaDrugi seminar mladih istraživača : Decembar 29, Beograd, 2003

Magnetic Properties of Mn-Doped Amorphous SiO2 Matrix

Samples of Mn-doped amorphous SiO2 matrix with manganese concentration 0.7 and 3 at.% have been prepared by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10 - 20 nm in size. Two types of Mn-rich particles are dispersed in silica matrix, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility reveals that dominant magnetic phase at higher temperatures is lambda-MnO2. At temperatures below T-C = 43 K strong ferrimagnetism originating from the minor Mn3O4 phase masks the relatively weak magnetism of lambda-MnO2. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the AC magnetic susceptibility in the sample with 3 at.% Mn suggest that the magnetic moments of the smaller Mn3O4 nanoparticles with dimensions below 10 nm are subject to thermally activated blocking process just below the Curie temperature T-C. The low-temperature maximum in the zero-field-cooled magnetization observed for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments in the geometrically frustrated Mn sublattice of the lambda-MnO2 crystal structure.12th Annual YUCOMAT Conference, Sep 06-10, 2010, Herceg Novi, Montenegr

Uticaj sive protivgradne mreže na kvalitet ploda borovnice (Vaccinium corymbosum L.) sorte "Bluecrop"

The main focus of our study was to investigate effects of the modified microclimate under a grey hail protection net (HPN) on biometrical fruit characteristics (fruit weight, index of fruit shape, and seed number per fruit) and nutritional value (soluble solid content - SSC, titratable acidity - TA, total anthocyanins - TACY, total phenolics - TPH and total antioxidant capacity - TAC) of the 'Bluecrop' highbush blueberry (Vaccinium corymbosum L.). The study was conducted in the 'Bluecrop' highbush blueberry plantation located in Mladenovac (Serbia) during two consecutive years (2013, 2014). The orchard was established using two-year-old nursery trees in spring 2011, at a planting density of 3,300 bushes per ha. The grey polyethylene net (SILVERLUX®, Helios Group, Lurano, Italy) with a Leno wave structure and a mesh size of 2.8 x 8 mm was used. During the research period, light intensity was measured weekly at 12.00 hr using a digital lux-meter 'Peak teck' PT-5025 (Germany). Air temperature and relative humidity within the canopy were recorded using climate dataloggers (type DT-171, Shenzhen Flus Technology Co., Ltd, China) both under HPN and in the open field (OF). Twelve readings per treatment were taken at 2-hour intervals every day in each season. In both years of observation, light was reduced by 5-20% under HPN, whereby daily maximum temperature was 2.4°C lower causing 4% higher daily minimum relative air humidity than in OF. 'Bluecrop' had significantly higher average fruit weights under HPN ranging from 1.93 g (2013) to 1.86 g (2014) in comparison to those observed in OF. The SSC did not differ between the treatments in 2014, whereas a significantly higher mean value was registered in the fruits harvested under HPN (12.8%) compared to those from OF in 2013. The mean TA was higher under HPN in 2014 (0.57%), whereas in 2013 a significantly higher TA content was found in OF (0.87%). HPN showed a positive effect on the TPH content (7.12 mg GA/g FW), but an almost 2-fold higher value was registered in 2013. Similar to this, TAC was 2.5-fold higher in 2013, without a significant effect of HPN in both experimental years.U ovom radu su ispitivani efekti izmenjene mikroklime pod sivom protivgradnom mrežom (PGM) na fizičke osobine ploda (masa ploda, indeks oblika ploda i broj semenki u plodu) i nutritivnu vrednost (sadržaj rastvorljive suve materije - RSM, ukupnih kiselina i ukupnih fenola, kao i ukupni antioksidativni kapacitet ploda) sorte borovnice "Bluecrop" (Vaccinium corymbosum L.). Ispitivanja su izvedena u periodu 2013-2014. godina, u zasadu borovnice koji se nalazi u blizini Mladenovca. Zasad je podignut u proleće 2011. godine sa trogodišnjim sadnicama i gustinom sadnje od 3.300 žbunova po ha. Primenjena je siva PGM (SILVERLUX®, Helios Group, Lurano, Italy), težine 48 g/m2, sa veličinom otvora 2,8 x 8 mm. Tokom perioda ispitivanja, intenzitet svetlosti je meren jedanput nedeljno u 12 h korišćenjem luks metra "Peak teck" PT-5025 (Germany). Temperatura i relativna vlažnost vazduha su merene uređajem za evidentiranje podataka (engl. data logger, DT-171, Shenzhen Flus Technology Co., Ltd, China) na svaka 2 h pod PGM i na otvorenom polju (kontrolni tretman) od početka cvetanja do kraja zrenja borovnice u obe ispitivane godine. Intenzitet svetlosti pod PGM je bio u proseku smanjen za 5-20% u obe eksperimentalne godine. Dnevne maksimalne temperature bile su za 2,4 oC niže pod PGM uslovljavajući za 4% višu minimalnu dnevnu relativnu vlažnost vazduha u poređenju sa otvorenim poljem. Značajno veća prosečna vrednost mase ploda kod ispitivane sorte borovnice registrovana je pod PGM u poređenju sa otvorenim poljem, i kretala se od 1,93 g (2013) do 1,86 g (2014). Sadržaj RSM se nije značajno razlikovao između tretmana u 2014. godini, dok je u 2013. godini značajno povećanje registrovano u plodovima koji su ubrani pod PGM (12,8%) u poređenju sa otvorenim poljem (11,6%). Prosečna vrednost sadržaja ukupnih kiselina je bila veća pod PGM u 2014. godini (0,57%), dok je u 2013. godini značajno veći sadržaj pronađen u plodovima ubranim na otvorenom polju (0,87%). PGM je ispoljila pozitivan efekat na sadržaj ukupnih fenola (7,12 mg galne kis. g-1sv.m.pl.), međutim skoro dva puta viša vrednost je bila registrovana u 2013. godini. Slično sadržaju ukupnih fenola, ukupni antioksidativni kapacitet ploda je bio za 2,5 puta veći u 2013. godini, bez značajnog uticaja PGM u obe ispitivane godine