1. 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: 10
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2. Energy intake models for intermittent operation of dead-end microfiltration filling lineJure Ravnik, Gorazd Bombek, Aleš Hribernik, Timi Gomboc, Matej Zadravec, Aleks Kapun, Grega Hrovat, Jure Gradišek, Matjaž Hriberšek, 2022, original scientific article Abstract: In filling lines equipped with membrane separation devices in the form of filters energy,
consumption is only one of the important working parameters, the other being sustainable filter
performance in terms of separation efficiency. As the filling line is typically equipped with a valve,
intermittent operation of the filter is an important form of its use. Whereas the overall energy
consumption of the filtration process is governed by the continuous operation mode, the intermittent
mode, characterised by opening/closing of the valve, contributes most to problems of filter failure,
i.e., the breakthrough of filtered particles through the membrane. A model for determination of the
energy intake of a microfiltration membrane during the opening and closing of a valve is presented
in this work. The model is based on computational analysis of the pressure wave signals recorded
during the opening/closing of the valve using Fourier transform, and expressed in a nondimensional
filter area specific energy intake form. The model is applied to a case of constant pressure dead-end
microfiltration with three filter types: a single membrane filter, a stacked filter and a pleated filter
with filtration surface areas ranging from 17.7 cm2
to 2000 cm2. Both clean filters, as well as partially clogged filter cases are taken into account. Second order polynomial models of the energy intake are developed and evaluated based on extensive analysis of the experimental data. The analysis of energy intake results show that the largest energy intake was observed for the clean filter case. When membrane fouling occurs at the constant flow rate values it leads to larger energy intake, however,
due to a decreasing specific flow rate during fouling these values do not exceed the clean filter case.
Keywords: membrane filtration, water hammer effect, membrane energy intake, filter clogging
Published in DKUM: 28.03.2025; Views: 0; Downloads: 1
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3. Experimental and mathematical investigation of anaerobic granulate density via settling velocityAljaž Klasinc, Gregor Drago Zupančič, Matjaž Hriberšek, Aleš Hribernik, Aleksandra Lobnik, Matej Zadravec, 2022, original scientific article Abstract: The objective of this study was to determine the density of anaerobic granules on different
heights of a full-scale Upflow Anaerobic Sludge Bed reactor. The density was defined through the
settling velocities of anaerobic granules, measured in a full-scale Upflow Anaerobic Sludge Bed
reactor. In this study, granular density was calculated with the measured settling velocities and
developed mathematical model. The developed mathematical model is based on the Stokes model.
In the experiment, granules were taken from different heights of an Upflow Anaerobic Sludge Bed
reactor, from 0.6 to 7.6 m. The granules’ diameters varied between 1 and 5 mm. The granules were
taken from six different heights through the reactor. The settling velocity of the active granules
(with gas in the granule pore and on the surface of the granule) was measured first. After the active
granules’ settling velocity measurement, the granules were placed in a vortex to obtain degassed
granules (granules without any gas in the pores or on the surface), for which the settling velocities
were also measured later. It is shown that granules’ densities at different heights are independent of
the reactor height.
Keywords: Upflow Anaerobic Sludge Bed reactor, microstructure, anaerobic granular sludge, settling velocity, density
Published in DKUM: 26.03.2025; Views: 0; Downloads: 5
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4. Synthesis of complex concentrated nanoparticles by Ultrasonic Spray Pyrolysis and lyophilisationLidija Simić, Srečko Stopić, Bernd Friedrich, Matej Zadravec, Žiga Jelen, Rajko Bobovnik, Ivan Anžel, Rebeka Rudolf, 2022, original scientific article Abstract: The development of new multicomponent nanoparticles is gaining increasing importance
due to their specific functional properties, i.e., synthesised new complex concentrated nanoparticles
(CCNPs) in the form of powder using ultrasonic spray pyrolysis (USP) and lyophilisation from the
initial cast Ag20Pd20Pt20Cu20Ni20 alloy, which was in the function of the material after its catalytic
abilities had been exhausted. Hydrometallurgical treatment was used to dissolve the cast alloy,
from which the USP precursor was prepared. As a consequence of the incomplete dissolution of
the cast alloy and the formation of Pt and Ni complexes, it was found that the complete recycling
of the alloy is not possible. A microstructural examination of the synthesised CCNPs showed that
round and mostly spherical (not 100%) nanoparticles were formed, with an average diameter of
200 nm. Research has shown that CCNPs belong to the group with medium entropy characteristics.
A mechanism for the formation of CCNPs is proposed, based on the thermochemical analysis of
element reduction with the help of H2 and based on the mixing enthalpy of binary systems.
Keywords: complex concentrated nanoparticles, ultrasonic spray pyrolysis, lyophilisation, characterization, formation mechanism
Published in DKUM: 24.03.2025; Views: 0; Downloads: 2
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5. Synthesis of Ni/Y2O3 nanocomposite through USP and lyophilisation for possible use as coatingTilen Švarc, Srečko Stopić, Žiga Jelen, Matej Zadravec, Bernd Friedrich, Rebeka Rudolf, 2022, original scientific article Abstract: The Ni/Y2O3 catalyst showed high catalytic activity. Based on this, the aim of this study
was to create Ni/Y2O3 nanocomposites powder with two innovative technologies, Ultrasonic Spray
Pyrolysis (USP) and lyophilisation. In the USP process, thermal decomposition of the generated
aerosols in an N2/H2 reduction atmosphere caused a complete decomposition of the nickel (II) nitrate
to elemental Ni, which became trapped on the formed Y2O3 nanoparticles. The Ni/Y2O3 nanocomposite particles were captured via gas washing in an aqueous solution of polyvinylpyrrolidone (PVP)
in collection bottles. PVP was chosen for its ability to stabilise nano-suspensions and as an effective
cryoprotectant. Consequently, there was no loss or agglomeration of Ni/Y2O3 nanocomposite material during the lyophilisation process. The Ni/Y2O3 nanocomposite powder was analysed using
ICP-MS, SEM-EDX, and XPS, which showed the impact of different precursor concentrations on the
final Ni/Y2O3 nanocomposite particle composition. In a final step, highly concentrated Ni/Y2O3
nanocomposite ink (Ni/Y2O3 > 0.140 g/mL) and test coatings from this ink were prepared by applying them on a white matte photo paper sheet. The reflection curve of the prepared Ni/Y2O3
nanocomposite coating showed a local maximum at 440 nm with a value of 39% reflection. Given that
Ni is located on the surface of the Ni/Y2O3 nanocomposite in the elemental state and according to the
identified properties, tests of the catalytic properties of this coating will be performed in the future.
Keywords: Ultrasonic Spray Pyrolysis (USP), lyophilisation, Ni/Y2O3 nanocomposite, characterisation, coatings
Published in DKUM: 20.03.2025; Views: 0; Downloads: 6
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6. Solidification of gelatine hydrogels by using a cryoplatform and its validation through CFD approachesYasir Beeran Potta Thara, Miha Jordan, Timi Gomboc, Blaž Kamenik, Boštjan Vihar, Vanja Kokol, Matej Zadravec, 2022, original scientific article Abstract: In this work, we developed a numerical approach based on an experimental platform
to determine the working conditions on a cryoplatform and to predict and evaluate the cryogenic
printing of hydrogels. Although hydrogels have good biocompatibility, their material properties
make it difficult to print them with high precision and shape fidelity. To overcome these problems, a
cryogenic cooling platform was introduced to accelerate the physical stabilisation of each deposited
layer during the printing process. By precisely controlling solidification (crystallisation), each printed
material can withstand its own weight to maintain shape fidelity, and the porosity of the scaffolds
can also be controlled more selectively. The thermophysical properties of gelatine hydrogels were
investigated to gain a better understanding of the phase change upon freezing. The corresponding
material properties and experimental observations of gelatine solidification served as the basis for
developing a computational fluid model (CFD) to mimic the solidification of gelatine hydrogels
using a cryoplatform at different process conditions and extruder speeds. The goal was to develop a
tool simple enough to predict acceptable process conditions for printing gelatine hydrogels using
a cryoplatform.
Keywords: gelatine, hydrogel, cryoprinting, CFD simulation, solidification modelling
Published in DKUM: 20.03.2025; Views: 0; Downloads: 7
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7. Towards a digital twin of primary drying in lyophilization using coupled 3-D equipment CFD and 1-D vial-scale simulationsMatej Zadravec, Efimia Metsi-Guckel, Blaž Kamenik, Johan Remelgas, Johannes G. Khinast, Nick Roscioli, Matthew Flamm, Harshil Renawala, Jeff Najarian, Atul Karande, Avik Sarkar, 2024, original scientific article Abstract: A digital twin of lyophilization units was developed to facilitate the scale-up of the lyophilization process from the laboratory to the commercial scale. Our focus was on ensuring successful technology transfer for manufacture of high-quality drug products. Traditionally, lyophilization models have been specific either to the equipment or to the vial. In this study, we integrated the equipment and the vial models in a way that they mutually influenced each other via boundary conditions (two-way coupling). We conducted two sets of calculations. Firstly, we performed steady-state simulations using Computational Fluid Dynamics (CFD) to simulate an ice slab test, which helped determine the equipment capability curve. Secondly, we carried out transient, coupled simulations using a coupled 3-D CFD and 1-D vial scale simulation model to mimic the primary drying phase in a lyophilizer. Using the coupled 3-D CFD and 1-D vial scale model, we were able to determine the product temperature, the sublimation rate and the cycle time based on the temporal and spatial conditions in the lyophilizer. The coupled approach was then applied to capture the effects of process disturbances and failure conditions in the lyophilizer, which enables a more robust process design.
Keywords: lyophilization, freeze-drying, sublimation
Published in DKUM: 13.03.2025; Views: 0; Downloads: 9
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8. Wear simulation of the conveyor belt transfer chute using the DEMTone Lerher, Žan Grum, Marko Motaln, Matej Zadravec, 2024, original scientific article Abstract: This paper presents a wear simulation-based performance evaluation of the conveyor belt transfer chute using the DEM (Discrete Element Method). Compared to known analytical and empirical wear models, DEM simulation can significantly increase the performance of wear analysis by enabling the analysis and optimization of highly complex geometries of material handling systems such as conveyor belt transfer chutes. Only the correct design of the conveyor belt transfer chute has the potential to significantly extend its service life, resulting in considerable cost savings. Based on the parametric analysis of different angles and radius in the upper head and lower section of the transfer chute, a new geometry of the transfer chute was proposed. The wear depth of the new conveyor belt transfer chute is compared with the wear resistant and low-carbon steel of the transfer chute along with the moderate and relatively high values of the solid granules mass flow. The results show that the wear depth of the transfer chute can be significantly reduced by using the wear-resistant steel compared to the low-carbon steel, which is significantly evident in high throughput rates of the solid granules mass flow.
Keywords: bulk material flow, Discrete Element Method (DEM), transfer chute wear simulation, archard and relative wear, performance analysis
Published in DKUM: 10.03.2025; Views: 0; Downloads: 9
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9. Sklopljeni numerični model prenosa gibalne količine, energije in snovi med procesom depozicije ledu v kondenzatorju liofilizatorja : magistrsko deloKlemen Meh, 2025, master's thesis Abstract: Magistrska naloga obravnava numerično modeliranje prenosa gibalne količine, energije in snovi med procesom depozicije ledu v kondenzatorju liofilizatorja. Osredotočili smo se na modeliranje robnega pogoja temperature na hladni steni kondenzatorja. Dosedanji numerični modeli so temeljili na konstantnem robnem pogoju temperaturnega profila na hladni steni kondenzatorja. V tem magistrskem delu pa smo izpeljali enačbe za izračun temperaturnega profila na hladni steni kondenzatorja in jih preizkusili na poenostavljenem modelu. Numerično smo simulirali stacionarne razmere s predpisanim robnim pogojem temperature na realnem modelu. Nato smo simulirali proces depozicije ledu v trajanju ene ure s pomočjo uporabniško definiranih funkcij pri dveh obratovalnih režimih. Ugotovili smo, da je učinkovitost kondenzatorja nekoliko nižja v primerjavi z dosedanjimi rezultati drugih raziskovalcev, dobljenih z upoštevanjem konstantnega robnega pogoja temperaturnega profila na hladni steni kondenzatorja. Razlika rezultatov med dvema različnima pristopoma pa ni izrazita. Naši rezultati so tudi skladni z ugotovitvami drugih avtorjev, ki so prav tako opazili, da je temperatura najvišja na mestu, kjer se začne hladilna tuljava, prav tako pa sta tam najintenzivnejša ponor vodne pare in depozicija ledu.
Keywords: prenosni pojavi, numerične simulacije, liofilizacija, kondenzator vodne pare, ANSYS Fluent, uporabniško definirane funkcije.
Published in DKUM: 05.02.2025; Views: 0; Downloads: 31
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10. Razvoj sistema za nadzor vlažnosti v mikrookolici nanopreciznega robota s Peltierjevim elementomSmiljana Milošević, 2024, undergraduate thesis Abstract: V diplomskem delu raziskujemo razvoj sistema za nadzor vlažnosti v mikrookolici nanopreciznega robota s Peltierjevim elementom. Cilj je bil ugotoviti, ali lahko Peltierjev element učinkovito regulira relativno vlažnost v komori za manipulacijo mikro objektov v nanorobotiki. Sistem uporablja senzorje za merjenje temperature in vlažnosti ter mikrokrmilnika Arduino in STM32 za vodenje sistema. Za upravljanje in prikaz rezultatov je bil razvit grafični vmesnik v programskem jeziku Python. Delo vključuje tudi modeliranje procesa in implementacijo PID regulatorja za optimizacijo nadzora vlažnosti.
Keywords: nanorobotika, Peltierjev element, Python, STM32, Ansys
Published in DKUM: 22.10.2024; Views: 0; Downloads: 32
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