1. Analysis of gas flow distribution in a fluidized bed using two-fluid model with kinetic theory of granular flow and coupled CFD-DEM: a numerical studyMatija Založnik, Matej Zadravec, 2025, original scientific article Abstract: Fluidized bed systems are widely used in chemical and process engineering due to their excellent heat and mass transfer properties. Numerical modeling plays a crucial role in understanding and optimizing these systems, with the two-fluid model enhanced by the kinetic theory of granular flow (TFM-KTGF) and the coupled computational fluid dynamics-discrete element method (CFD-DEM) emerging as leading techniques. This study employs both models to simulate gas-solid interactions and evaluates their performance using a benchmark single-spout fluidized bed case validated against experimental data. Subsequently, the influence of particle presence on gas flow distribution through a non-uniform distribution plate is analyzed. The results show that the common assumption of proportional flow distribution based on the opening area fraction is inaccurate, particularly in the presence of particles. Both numerical models capture this behavior, with TFM-KTGF showing trends comparable to the coupled CFD-DEM approach but at significantly reduced computational cost. The findings highlight the importance of accounting for particle dynamics in distribution plate design and promote the TFM-KTGF approach as a promising alternative for large-scale simulations.
Keywords: fluidized bed, distribution plate, two-fluid model with kinetic theory of granular flow, coupled CFD-DEM, flow distribution
Published in DKUM: 09.12.2025; Views: 0; Downloads: 7
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2. Numerical modelling of conjugate heat transfer in force convective flow environment using a combined boiling model (CBM)Jure Štrucl, Jure Marn, Matej Zadravec, 2025, original scientific article Abstract: Subcooled flow boiling is a crucial heat transfer mechanism in which the fluid temperature exceeds its saturation point, leading to phase change. Computational Fluid Dynamics (CFD) is a powerful tool for investigating such phenomena. However, commonly used CFD wall boiling models, such as the Rensselaer Polytechnic Institute (RPI) model, may under-predict convective heat transfer in flow boiling conditions, do not account for conjugate heat transfer (CHT), and often fail to accurately capture vapour flow behaviour after vapour detachment. This study presents a new model, named the Combined Boiling Model (CBM), which integrates CHT, wall boiling, and flow evaporation/condensation to improve predictive accuracy. Simulation results were compared against experimental data, demonstrating that the CBM accurately predicts heat transfer in channel flows with inlet velocities up to 1 m/s and heat fluxes up to 1.7 × 10⁶ W/m².
Keywords: boiling, evaporation, condensation, heat transfer, CHT, CFD
Published in DKUM: 28.11.2025; Views: 0; Downloads: 7
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3. CFD implementation and preliminary validation of a combined boiling model (CBM) for two-phase closed thermosyphonsJure Štrucl, Jure Marn, Matej Zadravec, 2025, original scientific article Abstract: Predicting phase-change heat transfer in two-phase closed thermosyphons (TPCTs) represents a significant challenge owing to the complex interaction of boiling, condensation, and conjugate heat transfer (CHT) mechanisms. This study presents a numerical investigation of a TPCT using the Combined Boiling Model (CBM) within a conjugate heat transfer (CHT) framework. Unlike prior TPCT studies, the CBM integrates an improved RPI-based wall boiling model with sliding bubble dynamics, a laminar film condensation closure, and Lee-type bulk phase change in a single, energy-consistent formulation suited for engineering-scale meshes and time-steps. Building on these extensions, we demonstrate the approach on a vertical TPCT with full CHT and validate it against experiments and a VOF–Lee reference. Simulations for heat loads ranging from 173 to 376 W capture key flow features, including vapour generation, vapour-pocket dynamics, and thin-film condensation, while reducing temperature deviations typically below 3% in the evaporator and adiabatic sections and about 2 to 5% in the condenser. The results confirm that the CBM provides a physically consistent and computationally efficient approach for predicting evaporation–condensation phenomena in TPCTs.
Keywords: heat pipe, thermosyphon, multiphase, conjugate heat transfer, Combined Boiling Model (CBM), Euler–Euler
Published in DKUM: 27.11.2025; Views: 0; Downloads: 5
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4. Optimizacija pretoka zraka v sušilni omariVid Ojsteršek, 2025, master's thesis Abstract: Magistrska naloga obravnava optimizacijo pretoka zraka v sušilni omari s toplotno črpalko. Glavni problem je neenakomerna porazdelitev zračnega toka po zadnji steni in stropu komore, kar negativno vpliva na učinkovitost in enakomernost sušenja perila. Namen raziskave je bil izboljšati tokovne razmere z nadgradnjo dveh ključnih komponent: ventilatorskega ohišja in zadnje stene, v katere so bili integrirani usmerniki zraka.
Raziskava temelji na kombinaciji eksperimentalnih meritev in numeričnih simulacij (CFD). Eksperimentalno je bil pretok merjen s senzorji AccuTrac, numerične simulacije pa so bile izvedene v programu Ansys Fluent z metodo končnih volumnov in modelom turbulence k-ω SST. Rezultati obeh pristopov so pokazali, da integracija usmernikov zagotavlja bolj enakomerno porazdelitev hitrosti zraka skozi odprtine na zadnji steni in stropu. Doseženo je bilo optimalno razmerje pretoka – približno 66 % skozi zadnjo steno in 34 % skozi strop – kar izboljša kroženje zraka v komori ter poveča učinkovitost in kakovost sušenja.
Delo potrjuje, da kombinacija numeričnega in eksperimentalnega pristopa omogoča učinkovito optimizacijo pretoka zraka v sušilnih napravah. Poleg tega naloga ponuja smernice za nadaljnje raziskave, kot so vključitev toplotnih izmenjevalcev v model, analiza vpliva vlage in akustičnih lastnosti ter preizkus alternativnih oblik odprtin.
Keywords: sušilna omara, optimizacija, toplotna črpalka, RDT simulacija, usmerniki
Published in DKUM: 20.11.2025; Views: 0; Downloads: 0
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5. Numerična analiza toka v laminarizatorju plinskega gorilnika : diplomsko deloMaj Tibaut, 2025, undergraduate thesis Abstract: Plinski gorilniki predstavljajo ključne elemente ogrevalnih sistemov, kjer sta učinkovitost zgorevanja in emisije škodljivih snovi odvisni od pretočnih karakteristik mešanice plinskega goriva. V tej študiji smo raziskali pretok skozi laminarizatorje plinskega gorilnika Weishaupt z namenom ugotoviti, ali se turbulentni tok znotraj njih ponovno laminarizira. Podrobno smo analizirali hitrostne profile skozi izbrane luknjice v pomanjšani geometriji ob upoštevanju vpliva lokacije, izbire medija (zrak ali vodik) ter primerjave med laminarnim in GEKO tokovnim modelom. Rezultati simulacij kažejo, da lokacija laminarizatorja in izbira medija pomembno vplivata na porazdelitev hitrosti zaradi kompleksne tridimenzionalne narave toka, medtem ko je vpliv izbire tokovnega modela zanemarljiv. Pridobljeni izsledki ponujajo trdno podlago za nadaljnjo optimizacijo geometrije in delovanja gorilnika.
Keywords: plinski gorilnik, laminarizator, cfd simulacija, turbulentni in laminarni tok, vodik
Published in DKUM: 03.10.2025; Views: 0; Downloads: 12
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6. Optimizacija porazdelitve lukenj na distribucijski plošči plinskega gorilnika na vodik : magistrsko deloValentin Planinšič, 2025, master's thesis Abstract: V magistrskem delu je obravnavana optimizacija porazdelitve lukenj na distribucijski plošči plinskega gorilnika, namenjenega zgorevanju vodika. S pomočjo numeričnih simulacij RDT v programu Ansys Fluent so bili analizirani vplivi geometrije plošče, velikosti lukenj, moči gorilnika ter vrste goriva na enakomernost porazdelitve pretoka skozi odprtine. Rezultati so pokazali, da velikost lukenj in vrsta goriva bistveno vplivata
na indeks uniformnosti in tlačne padce, pri čemer se pri vodiku izkaže, da je
enakomernost porazdelitve toka večja kot pri metanu. Na podlagi rezultatov so podana tudi priporočila za učinkovitejšo zasnovo distribucijskih plošč plinskih gorilnikov.
Keywords: plinski gorilnik, metan, vodik, distribucijska plošča, indeks uniformnosti, računalniška dinamika tekočin (RDT), numerična simulacija, tlačni padec
Published in DKUM: 01.10.2025; Views: 0; Downloads: 14
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7. Merjenje porazdelitve velikosti kapljic na šobi s pomočjo laserskega sistema : magistrsko deloSandi Sukič, 2025, master's thesis Abstract: V magistrskem delu smo preučevali sistem VisiSize za merjenje porazdelitve velikosti in hitrosti delcev. Postavili smo merilno progo in izvedli eksperimentalne meritve na razpršilni šobi. Uporabili smo različne masne pretoke ter tlake atomizacijskega zraka in zraka za oblikovanje vzorca, ter spremljali njihov vpliv na lastnosti delcev. Ugotovili smo, da tlaka zraka pomembno vplivata na velikost in hitrost delcev, medtem ko ima masni pretok manjši vpliv. Izvedli smo tudi meritve na različnih razdaljah od šobe. Izkazalo se je, da z ustreznimi nastavitvami lahko zagotovimo zanesljive in ponovljive rezultate, ki pomembno prispevajo k razvoju in optimizaciji razpršilnih naprav.
Keywords: velikost kapljic, velikost delcev, merilni sistem, laserski sistem, slikovna analiza
Published in DKUM: 19.06.2025; Views: 0; Downloads: 19
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8. A coupled multilevel vial lyophilization model for the pressure coupling in a freeze dryerBlaž Kamenik, Jure Ravnik, Timi Gomboc, Matej Zadravec, Matjaž Hriberšek, 2025, original scientific article Abstract: With computational modeling of lyophilization in vials, the pressure coupling between the sublimation front and the drying chamber has traditionally been calculated using a simplified mass transfer resistance model in the form of a model, which takes into account the headspace and the stopper in a simplified way. In developing a 3D CFD-based digital twin of lyophilization in vials, a need arises for a mass flow rate-dependent vial headspace/stopper model, as it enables a more accurate calculation of the pressure conditions above the shelf as well as pressure conditions directly at the sublimation front, the latter directly affecting the sublimation mass transfer rate as well as the temperature inside the product, which is crucial for determining the risk of product collapse. The local pressure variations at a shelf level affect the heat transfer conditions due to heat conduction in the low pressure environment of the drying chamber. In the present work the development of a coupled multilevel vial lyophilization model for the freeze-drying of vials is reported, with the time-dependent 1D heat and mass transfer model at the vial level coupled with the time-dependent 3D low-pressure CFD model of the flow of the water vapor–air mixture in the drying chamber heated by the shelves. A direct pressure coupling between the sublimation front and the drying chamber space in form of vial type specific headspace/stopper resistance model is implemented. The developed multilevel lyophilization model is used to study the pressure build-up above the shelf and the headspace of the vial and its influence on the product temperature at the bottom of the vial using simulations carried out for different chamber pressures (6 Pa and 22 Pa), shelf temperatures (−20 oC and +10 oC) and vial types (10R and 15R). By implementing previously developed vial headspace/stopper pressure resistance models, the computational results show that the pressure build-up above the shelf and vial headspace significantly affect the product temperature at the bottom of the vial, especially at low chamber pressures ( Pa) and small gap sizes between the rubber stopper and the shelf above it. The increased pressure outside the vial leads also to higher heat transfer by conduction, which is particularly pronounced at the central shelf positions and within smaller shelf gaps. These results underline the importance of using a coupled multilevel model when analyzing the relationship between the local pressure variations above the shelf and their direct influence on product drying conditions, further improving the predictive capabilities of CFD based multilevel lyophilization models, especially with respect to detecting the product collapse temperature.
Keywords: freeze-drying, conjugate heat and mass transfer, computational fluid dynamics, multi-scale modeling
Published in DKUM: 17.06.2025; Views: 0; Downloads: 14
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9. Konstruiranje in optimizacija stroja za mešanje in karbonizacijo pijač : magistrsko deloDenis Čuk, 2025, master's thesis Abstract: V magistrski nalogi se osredotočimo na konstruiranje in optimizacija stroja za mešanje in karbonizacijo pijač. Delo se opira na vhodne podatke specifičnega naročnika in vključuje proces optimizacije, ki obsega preračune in analize za določitev optimalne velikosti posameznih komponent. Cilj je bil konstruirati kompakten in učinkovit stroj z optimalno uporabo materialov in prostora.
Delo podrobno opisuje proces polnilne linije, vključno z mešanjem, deaeracijo, karbonizacijo in toplotno izmenjavo. Izbira ustreznih komponent temelji na viskoznosti, gostoti in zahtevani kapaciteti produkta. Pri izbiri komponent je upoštevana tudi higiena in skladnost z regulativnimi standardi živilske industrije.
Ključno vlogo v delu igra računalniško modeliranje in simulacije s programsko opremo Solidworks in Ansys. Z uporabo simulacij smo optimizirali višino mešala v mešalniku za optimalno mešanje, analizirali vpliv parametrov na učinkovitost sistema in s tem dosegli želeno kapaciteto in kakovost procesa.
Keywords: Stroj za mešanje in karbonizacijo pijač, mešalnik, polnilna linija, analiza mešanja, živilska industrija
Published in DKUM: 04.06.2025; Views: 0; Downloads: 29
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10. Numerična analiza aerodinamike vozila z metodo vstavljenega telesaRok Čeh, 2024, undergraduate thesis Abstract: Tema diplomskega dela je numerična analiza aerodinamike vozila z uporabo metode vstavljenega telesa, s katero želimo prikazati razliko v koeficientu zračnega upora pri različnih oblikah vozil. Analiza je bila izvedena na primeru aerodinamike vozila brez in z usmerjevalniki zračnega toka, katerega glavna funkcija je zmanjšanje koeficienta upora in je pritrjeno na podvozje vozila pred sprednjimi kolesi. Simulaciji sta bili izvedeni pri enaki hitrosti 130 km/h. Na podlagi dobljenih rezultatov smo ugotovili, da z omenjeno metodo vstavljenega telesa lahko prikažemo razliko v koeficientih upora pri različnih oblikah vozil.
Keywords: numerična analiza, računalniška dinamika tekočin (RDT), metoda vstavljenega telesa, aerodinamika, koeficient upora, usmerjevalniki
Published in DKUM: 11.04.2025; Views: 0; Downloads: 27
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