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1.
Analiza uporabe nanotekočin v toplotnih prenosnikih : magistrsko delo
Andrej Špiler, 2024, master's thesis

Abstract: V magistrskem delu je obravnavana simulacija toplotnega prenosnika v krožni zanki, v katerem je nanotekočina. Nanotekočina je stabilna suspenzija majhnih delcev v nosilni tekočini. V magistrskem delu je nosilni medij voda, v kateri so nanodelci Al2O3. Simulacija se je izvedla v programskem paketu Ansys Fluent. Geometrija toplotnega prenosnika je bila narejena po toplotnem prenosniku, uporabljenem pri eksperimentu, ki sta ga izvedla Cobanoglu in Haktan Karadeniz v delu ''Effect of nanofluic thermophysical propertis on the performance prediciton of single-phase natural ciculation loops'' [1]. Za opis snovnih lastnosti nanotekočin, ki so temperaturno in koncentracijsko odvisne, se je uporabil UDF (User Defined Function). Gibanje in obnašanje nanodelcev v tekočini se je v programski paket Ansys Fluent vstavilo kot UDS (User defined Scalar). Rezultati cevi premera 4,75 mm so se primerjali z rezultati iz eksperimenta [1] pri toplotnih močeh 10, 30 in 50 W. Naknadno so se naredile simulacije za premere 3, 4, 5 in 6 mm ter pregledal se je izkoristek glede na večanje koncentracije nanodelcev. Rezultati so pokazali, da se z višanjem koncentracije nanodelcev veča izkoristek toplotnega prenosnika in manjša hitrost tekočine.
Keywords: prenos toplote, toplotni prenosniki, nanodelci, nanotekočine, Ansys Fluent, UDF, UDS
Published in DKUM: 03.04.2024; Views: 177; Downloads: 25
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2.
Numerical simulations of the flow and aerosol dispersion in a violent expiratory event : Outcomes of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events
Jordi Pallares, Alexandre Fabregat Tomas, Akim Lavrinenko, Hadifathul Akmal bin Norshamsudin, Gabor Janiga, David Frederick Fletcher, Kiao Inthavong, Marina Zasimova, Vladimir Ris, Nikolay Ivanov, Robert Castilla, Pedro Javier Gamez-Montero, Gustavo Raush, Hadrien Calmet, Daniel Mira, Jana Wedel, Mitja Štrakl, Jure Ravnik, Douglas Hector Fontes, Francisco José De Souza, Cristian Marchioli, Salvatore Cito, 2023, original scientific article

Abstract: This paper presents and discusses the results of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events” aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of 7 research teams from different countries have performed a total of 11 numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier–Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in 12 simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceased.
Keywords: numerical simulations, computational fluid dynamics
Published in DKUM: 28.03.2024; Views: 374; Downloads: 449
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Coefficient of tangential restitution for non-spherical particles
Jana Wedel, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2024, original scientific article

Abstract: In various industrial and naturally occurring multiphase flows, whether dilute or dense, particle interaction plays a crucial role. In most cases, the particles are non-spherical, which poses a computational challenge in terms of particle motion and particle interaction, i.e. both particle–particle and particle–wall collisions. In this study, we present a novel frictional particle collision model to be used in general fluid flows. The model is derived for superellipsoidal particle shapes and thus allows consideration of frictional collisions of a wide variety of particle geometries. In this context, we derive an expression for the tangential coefficient of restitution applicable to arbitrarily shaped particles. Furthermore, we present the performance of the novel model by applying it to demonstrative examples ranging from two- to multi-particle systems.
Keywords: non-spherical particles, particle collision, tangential restitution coefficient, superellipsoids
Published in DKUM: 26.02.2024; Views: 221; Downloads: 16
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6.
Development of an experimental Dead-End microfiltration layout and process repeatability analysis
Gorazd Bombek, Luka Kevorkijan, Grega Hrovat, Drago Kuzman, Aleks Kapun, Jure Ravnik, Matjaž Hriberšek, Aleš Hribernik, 2024, original scientific article

Abstract: Microfiltration is an important process in the pharmaceutical industry. Filter selection and validation is a time-consuming and expensive process. Quality by design approach is important for product safety. The article covers the instrumentalization and process control of a laboratory-scale dead-end microfiltration layout. The layout is a downscale model of the actual production line, and the goal is filter validation and analysis of process parameters, which may influence filter operation. Filter size, fluid pressure, valve plunger speed, and timing issues were considered. The focus is on the identification of the most influential process parameters and their influence on the repeatability of pressure oscillations caused by valve opening. The goal was to find the worst-case scenario regarding pressure oscillations and, consequently, filter energy intake. The layout was designed as compact as possible to reduce pressure losses between the filter and valve. Valve-induced pressure oscillations proved to be prevailing over the water hammer effect. Several filters in sizes between 3.5 cm2 and 6900 cm2 were tested, and some recommendations were suggested for the reduction of energy intake of the filter and to improve the repeatability of the process.
Keywords: filtration, pressure oscillations, repeatability, processes, parameters
Published in DKUM: 01.02.2024; Views: 324; Downloads: 15
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7.
Numerical modeling of two-phase flow inside a wet flue gas absorber sump
Nejc Vovk, Jure Ravnik, 2023, original scientific article

Abstract: A numerical model of a flue gas scrubber sump is developed with the aim of enabling optimization of the design of the sump in order to reduce energy consumption. In this model, the multiphase flow of the continuous phase, i.e., water, and the dispersed phase, i.e., air bubbles, is considered. The air that is blown in front of the agitators, as well as the influence of the flow field of the agitators on the distribution of the dispersed phase and the recirculation pumps as outlet, is modeled. The bubble Sauter mean diameter is modeled using the population balance model. The model is used to analyze operating parameters such as the bubble retention time, the average air volume fraction, bubble Sauter mean diameter, the local distribution of the bubble size and the amount of air escaping from the pump outlets at two operating points. The purpose of the model is to simulate the two-phase flow in the sump of the flue gas scrubber using air dispersion technology with a combination of spargers and agitators, which, when optimized, reduces energy consumption by 33%. The results show that the homogeneity of air is lower in the bottom part of the absorber sump and that the amount of air escaping through recirculation pipes equals 1.2% of the total air blown into the absorber sump. The escaping air consists mainly of bubbles smaller than 6 mm. Additional operating point results show that halving the magnitude of the linear momentum source lowers the air retention, as well as the average homogeneity of the dispersed air
Keywords: flue gas scrubbing, air dispersion, numerical model, OpenFoam
Published in DKUM: 19.12.2023; Views: 278; Downloads: 18
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Numerično modeliranje dvofaznega toka v rezervoarju mokrega pralnika dimnih plinov : magistrsko delo
Nejc Vovk, 2023, master's thesis

Abstract: Za termoenergetske postroje so države postavile pravila, ki narekujejo omejitve emisij zdravju škodljivih plinov. Ta pravila so povzročila razvoj tehnologij čiščenja dimnih plinov, emitiranih iz termoenergetskih postrojev. Eden največjih onesnaževalcev je žveplov dioksid (SO2), ki nastaja pri zgorevanju premoga, onesnaženega z žveplom. V magistrskem delu obravnavamo mokri kalcitni postopek, ki zahteva izgradnjo pralnika dimnih plinov. V pralniku se žveplov dioksid absorbira v kapljice vode, v katerih je raztopljen apnenec. V reakciji ki poteče, nastane kalcijev sulfid (CaSO3), ki ob prenasičenju v vodi tvori kristale. Nastala suspenzija se zbira v spodnjem delu pralnika – rezervoarju, ki skrbi za tvorbo stabilnega produkta, kalcijevega sulfata (CaSO4). Slednje je izvedeno s prisilno oksidacijo, z uporabo kombinacije razpršilnih šob in mešal (agitatorjev), ki poskrbijo za čim daljši zadrževalni čas disperzne faze. Predstavljen je numerični model rezervoarja pralnika dimnih plinov, s katerim simuliramo večfazni tok v rezervoarju. V tem modelu obravnavamo tok zvezne faze (vode) in disperzne faze (mehurčkov zraka). Modelirano je vpihovanje zraka v področje pred agitatorji, vpliv tokovnega polja agitatorjev na distribucijo disperzne faze in obtočne črpalke, kot iztok tekočine iz rezervoarja. Razvoj Sauterjevega premera mehurčkov je modeliran po populacijskem modelu. Namen izdelave modela je bil analizirati vpliv obtočnih črpalk, ki domnevno motijo učinkovito disperzijo zraka. Rezultati kažejo, da izteka največ zraka skozi obtočno črpalko v skrajni legi, skupno pa skozi obtočne črpalke uhaja 1.2 % vpihanega zraka oz. 0.03 m3/s. Preračun je izveden v odprtokodnem programskem paketu OpenFoam v10, z uporabo superračunalniške infrastrukture v okviru projekta HPC RIVR.
Keywords: pranje dimnih plinov, disperzija zraka, numerični model, OpenFoam, superračunalnik
Published in DKUM: 23.08.2023; Views: 338; Downloads: 71
.pdf Full text (4,51 MB)

10.
Modeliranje prenosa sedimenta v Ptujskem jezeru : diplomsko delo
Filip Bezovnik, 2021, undergraduate thesis

Abstract: Človek lahko s posegom v rečno območje vpliva na proces prenosa sedimenta. Kolikšen je ta vpliv lahko izvemo z izdelavo modela prenosa sedimenta. V diplomski nalogi je predstavljena izdelava modela prenosa sedimenta s programom HEC-RAS. Poudarek je dan na enodimenzionalnem modelu z omembo dvodimenzionalnega modela prenosa sedimenta. Izdelan model je umerjen na povprečni rasti 4 lokacij v zadrževalniku voda. Simulacija je bila izvedena s hidravličnimi podatki iz leta 2020. Izdelan model ustrezno napove zvišanje rečnega dna v zadrževalniku voda. Napove, da se v zgornjem delu zadrževalnika voda usedejo vse večje frakcije od 0,064 mm. Del manjših frakcije pa se usede bližje jezu. Model tudi napove večjo sedimentacijo zgornjega dela zadrževalnika voda ob pretokih višjih od 600 m3/s za približno 7,86 ton glede na vstopno količino sedimenta v obravnavano območje. Izdelan model je uporaben za upravljavce Ptujskega jezera, saj z njim lahko ugotovijo intenzivnejša območja usedanja ter določijo način upravljanja, ki povzroči najmanjši dvig rečnega dna.
Keywords: modeliranje prenosa sedimenta, Ptujsko jezero, HEC-RAS, sedimentacija zadrževalnikov voda
Published in DKUM: 06.01.2022; Views: 1006; Downloads: 115
.pdf Full text (4,66 MB)

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