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..

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

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

Predviđanje dvofaznog strujanja sa generacijom pare oko cevi u snopu u isparivačima i generatorima pare

U hemijskoj industriji i energetici se koriste isparivači i generatori pare sa ključanjem na spoljašnjoj površini cevi koje formiraju cevni snop. Pri ključanju fluida dešavaju se složeni procesi prenosa toplote i mase koji određuju polje brzina obe faze, polje pritiska i raspored zapreminskog udela parne faze u ovim komponentama. Velike vrednosti zapreminskog udela pare mogu da izazovu krizu razmene toplote, koja se javlja u promenljivim ili prelaznim režimima kada je deo cevnog snopa okružen samo parnom fazom. Takođe, veliki protok dvofazne mešavine može da dovede do vibracija cevi isparivača ili generatora pare, dok recirkulacija tečnosti može da izazove taloženje primesa u pojedinim delovima generatora. Model predstavljen u ovom radu je podrška projektovanju i analizama rada generatora pare i isparivača. Zasnovan je na rešavanju bilansnih jednačina za svaku od faza u dvofaznom toku, uz primenu odgovarajućih konstitutivnih korelacija i omogućava izračunavanje brzinskog polja, polja pritiska i zapreminskog udela pare oko horizontalnog ili vertikalnog cevnog snopa, kao i predviđanje položaja dvofazne mešavin

Merenje nagiba kod gravitacionih betonskih brana primenom instrumenta tiltmetar

The measurement of inclination on gravity concrete dams using the instrument tiltmeter is described and discussed with special reference on obtained results on the dam 'Đerdap 2' acquired in the three years period. Tiltmetar way of operation is presented both through physical principle of vibrating wire sensors and through described design of the instrument. The influence of the temperature on the measurement of the slope is specially emphasized and presented through temperature correction. Processing the results of real inclination measurements on the dam 'Đerdap 2' with and without temperature correction showed the significant difference. Statistical analysis of measurement data consisted of performed regression analysis and forming of corresponding series with the expected measurement values depending on environmental conditions. At the end we give a summary conclusion on the instrument, the influence of temperature on the measurement and statistical model.U ovom radu prikazuje se način merenja nagiba kod gravitacionih betonskih brana primenom instrumenta tiltmetar, teorijski i preko opisa praktičnih merenja na brani 'Đerdap 2'. U prvom delu se objašnjava princip na kojem radi instrument tiltmetar i način na koji se vrši merenje nagiba primenom ovog instrumenta. Uticaj temperature na merenje nagiba je posebno razmatran kroz uvođenje temperaturske korekcije. U drugom delu se prikazuje obrada rezultata realnih merenja nagiba na jednom od instrumenata na brani 'Đerdap 2' sa i bez temperaturske korekcije. U trećem delu se prikazuje statistička obrada podataka merenja, u okviru koje se vrši regresiona analiza rezultata merenja i formiraju odgovarajuće serije sa očekivanim vrednostima merenja u zavisnosti od spoljašnjih uslova. Na kraju daje se sumarni zaključak o instrumentu, uticaju temperture na merenje i statistički model

SEED QUALITY OF NEW SOYBEAN VARIETIES PRODUCED IN SOUTH BAČKA IN 2011 YEAR KVALITET SEMENA NOVIH SORTI SOJE PROIZVEDENIH U JUŽNOJ BAČKOJ U 2011. GODINI

ABSTRACT REZIME Novostvorene sorte soje međusobno se razlikuju po morfološkim karakteristikama, zahtevima prema uslovima gajenja i tehnološ-kom kvalitetu zrna. Navedene razlike utiču na kvalitet semena i njegovu životnu sposobnost. Cilj rada je bio da se utvrdi kvalitet semena novih sorti soje koje se razlikuju u sadržaju proteina i ulja, kao i grupama zrenja. Ispitivanja semenskog kvaliteta izvršeno je na novim sortama soje stvorenim u Institutu za ratarstvo i povrtarstvo, Novi Sa

The usefulness of MMP-9, TIMP-1 and MMP-9/TIMP-1 ratio for diagnosis and assessment of COPD severity

Background: Inflammation, oxidative stress and an imbalance between proteases and protease inhibitors are recognized pathophysiological features of chronic obstructive pulmonary disease (COPD). The aim of this study was to evaluate serum levels of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) in patients with COPD and to assess their relationship with lung function, symptom severity scores and recent acute exacerbations. Methods: In this observational cohort study, serum levels of MMP-9 and TIMP-1 and the MMP-9/TIMP-1 ratio in the peripheral blood of COPD patients with stable disease and healthy controls were determined, and their association with lung function (postbronchodilator spirometry, body plethysmography, single breath diffusion capacity for carbon monoxide), symptom severity scores (mMRC and CAT) and exacerbation history were assessed. Results: COPD patients (n = 98) had significantly higher levels of serum MMP-9 and TIMP-1 and a higher MMP-9/TIMP-1 ratio than healthy controls (n = 47) (p ≤ 0.001). The areas under the receiver operating characteristic curve for MMP-9, TIMP-1 and the MMP-9/TIMP-1 ratio for COPD diagnosis were 0.974, 0.961 and 0.910, respectively (all p < 0.05). MMP-9 and the MMP-9/TIMP-1 ratio were both negatively correlated with FVC, FEV1, FEV1/FVC, VC, and IC (all p < 0.05). For MMP-9, a positive correlation was found with RV/TLC% (p = 0.005), and a positive correlation was found for the MMP-9/TIMP-1 ratio with RV% and RV/TLC% (p = 0.013 and 0.002, respectively). Patients with COPD GOLD 3 and 4 presented greater MMP-9 levels and a greater MMP-9/TIMP-1 ratio compared to GOLD 1 and 2 patients (p ≤ 0.001). No correlation between diffusion capacity for carbon monoxide and number of acute exacerbations in the previous year was found. Conclusions: COPD patients have elevated serum levels of MMP-9 and TIMP-1 and MMP-9/TIMP-1 ratio. COPD patients have an imbalance between MMP-9 and TIMP-1 in favor of a pro-proteolytic environment, which overall indicates the importance of the MMP-9/TIMP-1 ratio as a potential biomarker for COPD diagnosis and severity

Novi i značajni podaci o biljkama, algama i gljivama iz JI Evrope i susednih regiona, 16

This paper presents new records and noteworthy data on the following taxa in SE Europe and adjacent regions: diatoms Discostella asterocostata and Stephanodiscus hantzschii f. tenuis, red alga Bangia atropurpúrea, green alga Ulvapilifera, saprotro-phic fungi Didymella vitalbina and Phragmotrichum rivoclarinum, mosses Buxbau-mia aphylla, Sphagnum divinum, and Tortella fasciculata, monocots Anacamptis x nicodemi, Epipactis palustris, Epipogium aphyllum, and Gymnadenia frivaldii and dicots Androsace lactea, Drosera rotundifolia, Potentilla montenegrina, and Tozzia alpina subsp. carpathica are given within SE Europe and adjacent regions.U radu su prikazani novi i značajni podaci sa područja JI Evrope i susednih regiona o sledećim taksonima: dijatomejskim algama Discostella asterocostata i Stephanodiscus hantzschii f. tenuis, crvenoj algi Bangia atropurpurea, zelenoj algi Ulva pilifera, saprofitskim gljivama Didymella vitalbina i Phragmotrichum rivoclarinum, mahovinama Buxbaumia aphylla, Sphagnum divinum i Tortella fascicu- lata, monokotilama Anacamptis × nicodemi, Epipactis palustris, Epipogium aphyllum i Gymnadenia frivaldii i dikotilama Androsace lactea, Drosera rotundifolia, Potentilla montenegrina i Tozzia alpina subsp. carpathica

Set of Small Molecule Polyurethane (PU) Model Substrates: Ecotoxicity Evaluation and Identification of PU Degrading Biocatalysts

Polyurethanes (PUs) are an exceedingly heterogeneous group of plastic polymers, widely used in a variety of industries from construction to medical implants. In the past decades, we have witnessed the accumulation of PU waste and its detrimental environmental impacts. PUs have been identified as one of the most toxic polymers leaching hazardous compounds derived both from the polymer itself and the additives used in production. Further environmental impact assessment, identification and characterization of substances derived from PU materials and establishing efficient degradation strategies are crucial. Thus, a selection of eight synthetic model compounds which represent partial PU hydrolysis products were synthesized and characterized both in terms of toxicity and suitability to be used as substrates for the identification of novel biocatalysts for PU biodegradation. Overall, the compounds exhibited low in vitro cytotoxicity against a healthy human fibroblast cell line and virtually no toxic effect on the nematode Caenorhabditis elegans up to 500 µg mL−1, and two of the substrates showed moderate aquatic ecotoxicity with EC50 values 53 µg mL−1 and 45 µg mL−1, respectively, on Aliivibrio fischeri. The compounds were successfully applied to study the mechanism of ester and urethane bond cleaving preference of known plastic-degrading enzymes and were used to single out a novel PU-degrading biocatalyst, Amycolatopsis mediterranei ISP5501, among 220 microbial strains. A. mediterranei ISP5501 can also degrade commercially available polyether and polyester PU materials, reducing the average molecular number of the polymer up to 13.5%. This study uncovered a biocatalyst capable of degrading different types of PUs and identified potential enzymes responsible as a key step in developing biotechnological process for PU waste treatment options