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Numerična analiza tokovnih razmer v kondenzacijskem delu prenosnika toplote : magistrsko delo
Dejan Sevčnikar, 2024, magistrsko delo

Opis: V zmogljivih baterijskih električnih vozilih se kompaktni ploščni prenosniki toplote uporabljajo za zagotavljanje odvoda toplote iz kompresorskega parnega hladilnega kroga. V magistrskem delu smo obravnavali kondenzacijo hladiva v takšnem prenosniku toplote. Pripravili smo geometrijo prenosnika toplote in jo zamrežili s strukturirano mrežo. Izvedli smo analizo vpliva debeline elementa pri steni in analizo kalibracijskega parametra kondenzacijskega modela. Na podlagi rezultatov smo izbrali primerne kalibracijske vrednosti in izvedli variacijo masnega pretoka. Rezultate variacije masnega pretoka smo primerjali z meritvami iz referenčnega članka in ugotovili, da lahko, z uporabo navedenega modela, razmeroma natančno napovemo prestop toplote in suhost pare za izbrani primer. Prav tako smo s simulacijo potrdili trende, ki se pojavljajo pri spremembah masnega pretoka in suhosti pare.
Ključne besede: kondenzacija, numerična analiza, prenosnik toplote, hladivo
Objavljeno v DKUM: 22.04.2024; Ogledov: 89; Prenosov: 0
.pdf Celotno besedilo (6,20 MB)

Study of ▫$Ni/Y_2O_3/polylactic$▫ acid composite
Tilen Švarc, Matej Zadravec, Žiga Jelen, Peter Majerič, Blaž Kamenik, Rebeka Rudolf, 2023, izvirni znanstveni članek

Opis: This study demonstrates the successful synthesis of Ni/Y2O3 nanocomposite particles through the application of ultrasound-assisted precipitation using the ultrasonic spray pyrolysis technique. They were collected in a water suspension with polyvinylpyrrolidone (PVP) as the stabiliser. The presence of the Y2O3 core and Ni shell was confirmed with transmission electron microscopy (TEM) and with electron diffraction. The TEM observations revealed the formation of round particles with an average diameter of 466 nm, while the lattice parameter on the Ni particle’s surface was measured to be 0.343 nm. The Ni/Y2O3 nanocomposite particle suspensions were lyophilized, to obtain a dried material that was suitable for embedding into a polylactic acid (PLA) matrix. The resulting PLA/Ni/Y2O3 composite material was extruded, and the injection was moulded successfully. Flexural testing of PLA/Ni/Y2O3 showed a slight average decrease (8.55%) in flexural strength and a small decrease from 3.7 to 3.3% strain at the break, when compared to the base PLA. These findings demonstrate the potential for utilising Ni/Y2O3 nanocomposite particles in injection moulding applications and warrant further exploration of their properties and new applications in various fields.
Ključne besede: ultrasound spray pyrolysis, Ni/Y2O3, lyophilization, PLA, extrusion, injection moulding
Objavljeno v DKUM: 05.04.2024; Ogledov: 108; Prenosov: 8
.pdf Celotno besedilo (3,29 MB)
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Design of an Efficient Fan Steering Strategy for Efficient Cooling of Engine Peripheral Components during Vehicle Thermal Soak : magistrsko delo
Tjaša Pečnik, 2024, magistrsko delo

Opis: The aim of this Master's thesis was to find a mathematical correlation between various fan momentum fields for a fan which is used for cooling the underhood area of a car. The correlation had to link a known momentum field to all possible momentum fields related to fan rotation speed and car velocity. With this correlation, new alternative fan steering strategies can be used to cool the vehicle underhood area. An already functioning RBM (Rigid Body Motion) simulation was used as a base, since it already gave satisfying results in the past. With this simulation file, several tests were run to ensure that the results really converge nicely. In this way it was established that the results are accurate enough for further use. After obtaining the results, a set of 30 simulation files was calculated. The simulations were a combination of different fan rotation speeds and car velocities. After the set was done, the results were analysed using various computer software (Star-CCM+, MS Excel and Matlab). It was concluded that a polynomial approach for the momentum field was a suitable option but to add some additional complexity, surface equations were used. To obtain the equations, tables with different results were put into Matlab and the program did the rest. The result were two sets of three surface equations with x and y values. In both cases, x represented the rotation speed of the fan and y represented the car velocity in one case and the delta pressure between two evaluation surfaces in the other. After that it was time to implement the newly acquired surface equations in a Star-CCM+ simulation file. The old simulation file was again used as a base, but new field functions were put in with the help of which the UDMS (User Defined Momentum Source) is being changed. Both types of surface equations were tested and calculated. In the end, it was decided to go with the one where the delta pressure on two evaluation surfaces is being used as the y value. One surface was placed in front of the fan and the other after the fan. The final step was to test different fan steering strategies. The usual cooling procedure consists of a phase where the fan cools for a specific amount of time with a defined rotation speed and then turns off. Temperatures on critical points around the engine and in the underhood area of the car are being looked at as a result. The first strategy was to run the fan at the same speed as usual, but gradually slow it down in uniform steps so that the shut down time remains the same. With this approach, the highest temperature values were actually lower than usual, but certain temperature probes became warmer as the fan speed decreased. Nevertheless, the temperatures at the end were very similar. The second tested strategy was inspired by the idea of potentially saving some battery energy if we could somehow manage to cool the underhood area quicker. In this case, the fan ran for a short time at a high rotation speed and after that at a slightly lower speed. Then it was turned off for a few minutes and subsequently switched back on. The maximum temperature in this scenario reached even higher values. The reason for this was that the fan blew warm air toward certain measurement points, causing them to heat up further. The temperatures at the end of the simulation were similar to those in the previous two cases. In conclusion, it is indeed possible to steer a fan momentum field with the help of field functions and equations which describe the relationship between different fan rotation speeds and car velocities.
Ključne besede: fan, momentum, RBM, CFD, thermal soak
Objavljeno v DKUM: 02.04.2024; Ogledov: 112; Prenosov: 0
.pdf Celotno besedilo (13,61 MB)

Numerično modeliranje dvofaznega toka v mali čistilni napravi : diplomsko delo
Žan Frumen, 2022, diplomsko delo

Opis: V diplomskem delu je s pomočjo računalniške dinamike tekočin, opravljena numerična analiza dvofaznega toka v mali čistilni napravi. Predstavljene so geometrijske lastnosti ter vplivni parametri, kot tudi aeracija v mali čistilni napravi. V nadaljevanju je predstavljeno teoretično ozadje modeliranja. Izpeljana sta tudi ohranitvena zakona mase in gibalne količine. Izvedena je bila poliedrična mreža, analiza vplivnih parametrov pretoka in velikosti mehurčka zraka na aeracijo. Na koncu je bil računan indeks uniformnosti porazdelitve volumskega deleža zraka v mali čistilni napravi. Ugotovljene in predstavljene so optimalne razmere za opravljeno simulacijo.
Ključne besede: mala čistilna naprava, računalniška dinamika tekočin, ANSYS Fluent, aeracija, simulacija
Objavljeno v DKUM: 05.03.2024; Ogledov: 182; Prenosov: 12
.pdf Celotno besedilo (2,36 MB)

Recovery study of gold nanoparticle markers from lateral flow immunoassays
Tilen Švarc, Peter Majerič, Darja Feizpour, Žiga Jelen, Matej Zadravec, Timi Gomboc, Rebeka Rudolf, 2023, izvirni znanstveni članek

Opis: Lateral flow immunoassays (LFIAs) are a simple diagnostic device used to detect targeted analytes. Wasted and unused rapid antigen lateral flow immunoassays represent mass waste that needs to be broken down and recycled into new material components. The aim of this study was to recover gold nanoparticles that are used as markers in lateral flow immunoassays. For this purpose, a dissolution process with aqua regia was utilised, where gold nanoparticles were released from the lateral flow immunoassay conjugate pads. The obtained solution was then concentrated further with gold chloride salt (HAuCl4) so that it could be used for the synthesis of new gold nanoparticles in the process of ultrasonic spray pyrolysis (USP). Various characterisation methods including scanning electron microscopy, transmission electron microscopy, ultraviolet-visible spectroscopy and optical emission spectrometry with inductively coupled plasma were used during this study. The results of this study showed that the recovery of gold nanoparticles from lateral flow immunoassays is possible, and the newly synthesised gold nanoparticles represent the possibility for incorporation into new products.
Ključne besede: gold nanoparticles, recovery, LFIA, ultrasonic spray pyrolysis, characterisation
Objavljeno v DKUM: 09.02.2024; Ogledov: 217; Prenosov: 15
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Reconstruction of a fluid bed device for separating granular material from the grinding process of rapid antigen tests
Miha Jordan, Tilen Švarc, Peter Majerič, Rebeka Rudolf, Matej Zadravec, 2023, izvirni znanstveni članek

Opis: The article includes the study and reconstruction of a fluid bed device with the purpose of separating the granular material from the grinding process of rapid antigen tests. The following techniques were performed, with the purpose of characterisation of the ground particles: sieve analysis, X-ray fluorescence spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. The paper includes experimental testing of a simplified separation process with zeolite spheres and paper strips, supported by a numerical model. The flow conditions’ impact on the behaviour and interactions of particles of the considered problem were simulated using coupled computational fluid dynamics (CFD) and the discrete element method (DEM) approach. The separation process of zeolite spheres and paper strips was found to be efficient. The simulation results showed the appropriate behaviour of the particles during the process. We explained the results’ deviations, and we also presented the shortcomings and possible improvements. Further research is required to define the adequacy of the process, while using actual ground material of rapid antigen tests.
Ključne besede: rapid antigen tests, nanomaterials, fluidised bed, computational fluid dynamics, discrete element method, characterisation
Objavljeno v DKUM: 05.01.2024; Ogledov: 266; Prenosov: 22
.pdf Celotno besedilo (4,21 MB)
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Modeliranje toka krvi skozi žilno opornico z uporabo večfaznega modela zvezne tekočine
Jaka Bezjak, 2023, magistrsko delo

Opis: V tem delu je predstavljen pristop modeliranja toka krvi kot enofazni in večfazni sistem, skozi žilno opornico na poenostavljeni geometriji. Predstavljene so bile dosedanje ugotovitve na področju računske dinamike tekočin krvi, vodilne enačbe v posameznem pristopu ter trije pristopi večfaznega sistema. Za večfazni pristop je bil izbran pristop Euler-Euler. V enofaznem sistemu je kri obravnavana kot Newtonska ter nenewtonska tekočina, medtem ko je v večfaznem sistemu obravnavana kot štiri fazna zmes. Izvedene so bile tri simulacije ustaljenih razmer ter ena časovno odvisna simulacija na enofaznem nenewtonskem modelu. Za izvedbo simulacij je bil uporabljen programski paket ANSYS Fluent 2023 r1. Rezultati so bili analizirani v programu CFD Post, kjer smo opazovali vpliv žilne opornice na strižno napetost. Opazili smo področja manjše strižne napetosti med opornicami ter razlike med notranjo in zunanjo stranjo žile. Dobljene rezultate smo primerjali z referenčnim člankom. Enofazni modeli so bili skladni s člankom, pri čemer je bil nenewtonski model malenkost boljši, medtem ko so rezultati večfaznega modela bistveno odstopali. Iz tega smo sklepali, da je za potrebe analiziranje žilne opornice pristop enofazne tekočine primernejši, medtem ko je prednost večfaznega modela v možnosti vpogleda porazdelitev posameznih faz oziroma krvnih delcev. Na koncu smo tudi našteli omejitve večfaznega pristopa in raziskali možnosti za izboljšavo.
Ključne besede: Tok krvi, opornica, nenewtonska tekočina, večfazni sistem, numerična simulacija, strižna napetost.
Objavljeno v DKUM: 04.01.2024; Ogledov: 266; Prenosov: 17
.pdf Celotno besedilo (4,61 MB)

Povečanje energetske učinkovitosti in postavitev procesa obdelave granuliranega materiala v končni produkt : magistrsko delo
Jana Stanič, 2023, magistrsko delo

Opis: Dandanes so procesi proizvodnje granuliranih materialov ključni v številnih obratih zato je pomembno, da so sistemi pravilno načrtovani in dimenzionirani za njihovo optimalno delovanje. To zahteva upoštevanje ustreznih masnih tokov, volumskih pretokov in moči naprav, ki so vključene v proces. V magistrskem delu je predstavljena masna in energijska bilanca procesa obdelave granuliranega materiala, ter postavitev le-tega v končni produkt. V delu je prav tako predstavljen način, kako s prisilnim hlajenjem končnega produkta povečati energetsko učinkovitost procesa.
Ključne besede: granulirani material, masna bilanca, energijska bilanca
Objavljeno v DKUM: 28.11.2023; Ogledov: 345; Prenosov: 26
.pdf Celotno besedilo (1,74 MB)

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