Iskanje po katalogu digitalne knjižnice

Opis: V diplomskem delu je predstavljena študija prenosa toplote iz police liofilizatorja na viale. Predstavljeno je teoretsko ozadje prenosa toplote ter procesa liofilizacije. S pomočjo numeričnih simulacij smo analizirali prenos toplote na realno ter poenostavljeno geometrijo viale 10R, pri čemer smo z definiranjem toplotnega upora med vialo in polico liofilizatorja poenostavljene geometrije opisali toplotne razmere v realni viali. Rezultate simulacij smo primerjali z eksperimentalno pridobljenimi temperaturnimi poteki ohlajanja destilirane vode v vialah. V diplomskem delu smo ugotovili, da je za validacijo numerične simulacije z eksperimentalnimi rezultati ključno poznavanje masnega toka grelno-hladilnega medija v policah liofilizatorja, ki bistveno vpliva na intenziteto prenosa toplote iz polic liofilizatorja na viale.
Ključne besede: prenos toplote, liofilizacija, računalniška dinamika tekočin, viala
Objavljeno v DKUM: 02.10.2025; Ogledov: 0; Prenosov: 15
Celotno besedilo (4,39 MB)

Opis: 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.
Ključne besede: freeze-drying, conjugate heat and mass transfer, computational fluid dynamics, multi-scale modeling
Objavljeno v DKUM: 17.06.2025; Ogledov: 0; Prenosov: 14
Celotno besedilo (4,01 MB)
Gradivo ima več datotek! Več...

Opis: 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.
Ključne besede: gelatine, hydrogel, cryoprinting, CFD simulation, solidification modelling
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 12
Celotno besedilo (5,41 MB)
Gradivo ima več datotek! Več...

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: 6
Celotno besedilo (2,88 MB)

Opis: 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.
Ključne besede: prenosni pojavi, numerične simulacije, liofilizacija, kondenzator vodne pare, ANSYS Fluent, uporabniško definirane funkcije.
Objavljeno v DKUM: 05.02.2025; Ogledov: 0; Prenosov: 41
Celotno besedilo (7,82 MB)