1. A coupled point particle two-phase heat and mass transfer model for dispersed flows based on Boundary Element MethodsTimi Gomboc, Matej Zadravec, Jure Ravnik, Matjaž Hriberšek, 2024, published scientific conference contribution Abstract: In dispersed multiphase flow processes we encounter coupled heat, mass and momentum transfer between the disoersed and the continuous phase. In the context of the subdomain Boundary Domain Integral Method (BDIM) solution of the Navier-Stokes equations a two-way coupling model is presented based on the use of the elliptic fundamental solution and the Dirac delta function properties which leads to accurate evaluation of the heat and mass point particle source impacts on the continuous (air) phase. In addition, the two-phase flow case under consideration is extended to the case of porous spherical particle drying with internal moving drying front, which is solved by the Boundary Element Method (BEM).
Keywords: heat transfer, mass transfer, Boundary Element Methods
Published in DKUM: 01.07.2024; Views: 113; Downloads: 15
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2. Saponification reaction system : a detailed mass transfer coefficient determinationDarja Pečar, Andreja Goršek, 2015, original scientific article Abstract: The saponification of an aromatic ester with an aqueous sodium hydroxide was studied within a heterogeneous reaction medium in order to determine the overall kinetics of the selected system. The extended thermo-kinetic model was developed compared to the previously used simple one. The reaction rate within a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as mass transfer between both phases. Chemical rate constant was obtained from experiments within a homogeneous medium, whilst the mass-transfer coefficient was determined separately. The measured thermal profiles were then the bases for determining the overall reaction-rate.
This study presents the development of an extended kinetic model for considering mass transfer regarding the saponification of ethyl benzoate with sodium hydroxide within a heterogeneous reaction medium. The time-dependences are presented for the mass transfer coefficient and the interfacial areas at different heterogeneous stages and temperatures.
The results indicated an important role of reliable kinetic model, as significant difference in $k_La$ product was obtained with extended and simple approach.
Keywords: chemical kinetics, mass transfer, saponification, heterogeneous system
Published in DKUM: 25.08.2017; Views: 1794; Downloads: 226
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3. Separation of parthenolide from feverfew: performance of conventional and high-pressure extraction techniquesLucija Čretnik, Mojca Škerget, Željko Knez, 2005, original scientific article Abstract: In present work the extraction of feverfew flower heads was performed using supercritical carbon dioxide at pressures from 200 to 800 bar and at temperatures of 40, 60 and 80 °C. For comparison, the conventional extractionswith organic solvents have been performed. Dry feverfew flower heads were used as starting material. Supercritical fluid extraction (SFE) wasperformed using a semi continuous flow apparatus in a laboratory and pilot scale. The influence of process parameters on the total yield and amount of parthenolide isolated was investigated. Dynamic behaviour of the extraction runs followed by single-step separation was analysed by a mathematical model for initial constant rate extraction period and the subsequent time-dependant diffusion controlling mass transfer rate period. In order to concentrate the obtained extract in parthenolide, a two-step separation was employed.
Keywords: chemical processing, high pressure extraction, conventional extraction, supercritical CO2, parthenolide, feverfew, extraction rate, mass transfer
Published in DKUM: 01.06.2012; Views: 2114; Downloads: 108
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4. Use of genetic algorithm for fitting Sovova's mass transfer modelDejan Hrnčič, Marjan Mernik, Maša Knez Marevci, 2010, original scientific article Abstract: A genetic algorithm with resizable population has been applied to the estimation of parameters for Sovovaćs mass transfer model. The comparison of results between a genetic algorithm and a global optimizer from the literatureshows that a genetic algorithm performs as good as or better than a global optimizer on a given set of problems. Other benefits of the genetic algorithm, for mass transfer modeling, are simplicity, robustness and efficiency.
Keywords: Sovova's mass transfer model, genetic algorithm, parameter estimation
Published in DKUM: 31.05.2012; Views: 1902; Downloads: 89
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5. Extraction of lutein from Marigold flower petals - Experimental kinetics and modellingMaša Hojnik Niderl, Mojca Škerget, Željko Knez, 2008, original scientific article Abstract: The extraction kinetics behaviour of lutein from Marigold flower petals and simultaneous alkali hydrolysis has been studied. Extraction was carried out by varying following operating conditions: type of organic solvent, temperature, ratio liquid: material, concentration of alkali solution, and particle size of plant material. Experimental extraction curves were analysed with a mathematical model derived from Fick's second law. The extraction of lutein appeared to be governed by slow and fast diffusion processes. Results showed that the intra-particle diffusion was the rate-governing step of the extraction process, and that the chosen model gives very good approximation of experimental data.
Keywords: lutein, marigold, conventional extraction, diffusivity, mass transfer
Published in DKUM: 31.05.2012; Views: 2372; Downloads: 112
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6. Determination of the process parameters relative influence on k[sub]La value using Taguchi design methodologyMarko Tramšek, Andreja Goršek, 2007, original scientific article Abstract: This article describes experimental determination of the relative impact of significant process parameters that influence volumetric oxygen mass transfer coefficient (kLa) using Taguchi design methodology. For this purpose an automated RC1 reaction calorimeter (Mettler-Toledo), which was originally developed for chemical processes, was modified for the bioprocesses. Simple fermentation using Baker's yeast was studied to illustrate the design procedure. Orthogonal array L25 was selected for the proposed design and ANOVA method was used for recognizing the relative influence of the process parameters. Within the observed range of temperature (?), fermentation media volume (VFM), and yeast mass concentration (?Y), these process parameters were found to be unimportant compared to the volumetric air flow rate (qV,a) and rotational frequency of the stirrer (fm). The qV,a had a substantial effect on the kLa value (89.2 %) and the fm had just a small one (3.6 %), meanwhile the remain fraction to 100 % represents error. The results refer strictly to the selected case study. Anyhow, the proposed procedure shows that application of the Taguchi approach for analyzing the oxygen mass transfer based on the experimental data obtained from a highly-automated laboratory reactor appears to have potential usage in general biopharmaceutical process design.
Keywords: bioprocess parameters, mass transfer, volumetric oxygen mass transfer coefficient, process parameters, Taguchi method, analysis of variance
Published in DKUM: 31.05.2012; Views: 2551; Downloads: 54
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