1. Advancing nanofluid numerical modelling: A novel Euler–Lagrange method with experimental validationNejc Vovk, Blaž Kamenik, Elif Begum Elcioglu, Erdem Ozyurt, Ziya Haktan Karadeniz, Alpaslan Turgut, Jure Ravnik, 2025, izvirni znanstveni članek Opis: We present a novel approach to numerical modelling of thermal nanofluids based on the Euler–Lagrange method. This approach overcomes the challenge of extremely fine temporal discretization, which previous Euler–Lagrange nanofluid numerical models struggled to address, while also avoiding the need for too many Lagrangian nanoparticles. A numerical uncertainty assessment method is adapted for the proposed approach. The model is validated with a simple verification case and applied to simulate a closed natural circulation loop heat exchanger operating with heating power ranging from 10 W to 50 W and nanoparticle volume fractions of 0.5% to 2%, using an Al2O3–water nanofluid. Results are compared with experimental temperature measurements and an Euler–Euler implementation of the same nanofluid. The model is also applied to simulate the natural convection inside a vertical enclosure, studied experimentally by other authors. The proposed novel approach demonstrates agreement with both experimental data and the Euler–Euler implementation, effectively capturing the overall behaviour of nanofluids. We establish, that the interplay of multiple transport phenomena, that occur in nanofluid operated devices, can be difficult to completely reproduce numerically within the framework of current modelling assumptions.
Ključne besede: Euler–Lagrange nanofluid modelling, numerical uncertainty assessment, natural convection loop simulation, nanoparticle concentration analysis, nanofluid heat transfer
Objavljeno v DKUM: 17.06.2025; Ogledov: 0; Prenosov: 3
 Celotno besedilo (3,33 MB)
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2. Euler–Euler numerical model for transport phenomena modeling in a natural circulation loop operated by nanofluidsBlaž Kamenik, Nejc Vovk, Elif Begum Elcioglu, Firat Sezgin, Erdem Ozyurt, Ziya Haktan Karadeniz, Alpaslan Turgut, Jure Ravnik, 2025, izvirni znanstveni članek Opis: This paper explores a computational approach to model multiphase heat transfer and fuid fow in a natural circulation loop utilizing nanofuids. We propose and implement an Euler–Euler framework in a CFD environment, incorporating an innovative boundary condition to preserve mass conservation during thermophoretic particle fux. The model’s accuracy is verifed through a one-dimensional example, by comparing results against both an Euler–Lagrange model and an in-house fnite volume solution. Experimental validation is conducted with aluminum oxide nanofuids at varying nanoparticle concentrations. We prepared the nanofuids and measured their thermophysical properties up to 60◦C. We assess the thermal performance of the nanofuid in natural circulation loop at diferent heating powers via experiment and numerical simulations. The fndings reveal that the heat transfer enhancement ofered by the nanofuid is modest, with minimal diferences observed between the proposed Euler–Euler approach and a simpler single-phase model. The results underscore that while the Euler–Euler model ofers detailed particle–fuid interactions, its practical thermal advantage is limited in this context.
Ključne besede: CFD · Euler–Euler, multiphase fow, nanofluid, natural circulation loop, thermophoresis
Objavljeno v DKUM: 12.03.2025; Ogledov: 0; Prenosov: 5
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3. Numerical modeling of two-phase flow inside a wet flue gas absorber sumpNejc Vovk, Jure Ravnik, 2023, izvirni znanstveni članek Opis: 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
Ključne besede: flue gas scrubbing, air dispersion, numerical model, OpenFoam
Objavljeno v DKUM: 19.12.2023; Ogledov: 359; Prenosov: 81
Celotno besedilo (41,41 MB)
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4. Numerično modeliranje dvofaznega toka v rezervoarju mokrega pralnika dimnih plinov : magistrsko deloNejc Vovk, 2023, magistrsko delo Opis: 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.
Ključne besede: pranje dimnih plinov, disperzija zraka, numerični model, OpenFoam, superračunalnik
Objavljeno v DKUM: 23.08.2023; Ogledov: 423; Prenosov: 127
Celotno besedilo (4,51 MB) |
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