1. Quadratic time elements for time-dependent fundamental solution in the BEM for heat transfer modelingIvan Dominik Horvat, Jurij Iljaž, 2024, izvirni znanstveni članek Opis: In this paper, a quadratic time interpolation for temperature and a linear time interpolation for fluxes are implemented for the parabolic (time-dependent) fundamental solution-based scheme for solving transient heat transfer problems with sources using the subdomain BEM (boundary element method), which is the main innovation of this paper. The approach described in this work to incorporate the quadratic time variation does not require doubling the number of equations, which is otherwise required in the BEM literature, for the discretized problem to be well-conditioned. Moreover, the numerical accuracy, compared over an unprecedented range of the Fourier number (Fo) and source strength values, can help in selecting the appropriate scheme for a given application, depending on the rate of the heat transfer process and the included source term. The newly implemented scheme based on the parabolic fundamental solution is compared with the well-established elliptic (Laplace) scheme, where the time derivative of the temperature is approximated with the second-order finite difference scheme, on two examples.
Ključne besede: quadratic time elements, time-dependent fundamental solution, heat transfer modeling, boundary element method
Objavljeno v DKUM: 07.05.2025; Ogledov: 0; Prenosov: 3
 Celotno besedilo (8,22 MB)
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2. Valorization of biomass through anaerobic digestion and hydrothermal carbonization : integrated process flowsheet and supply chain network optimizationSanja Potrč, Aleksandra Petrovič, Jafaru Musa Egieya, Lidija Čuček, 2025, izvirni znanstveni članek Opis: Utilization of biomass through anaerobic digestion and hydrothermal carbonization is crucial to maximize resource efficiency. At the same time, supply chain integration ensures sustainable feedstock management and minimizes environmental and logistical impacts, enabling a holistic approach to a circular bioeconomy. This study presents an integrated approach to simultaneously optimize the biomass supply chain network and process flowsheet, which includes anaerobic digestion, cogeneration, and hydrothermal carbonization. A three-layer supply chain network superstructure was hence developed to integrate the optimization of process variables with supply chain features such as transportation modes, feedstock supply, plant location, and demand location. A mixed-integer nonlinear programming model aimed at maximizing the economic performance of the system was formulated and applied to a case study of selected regions in Slovenia. The results show a great potential for the utilization of organic biomass with an annual after tax profit of 23.13 million USD per year, with the production of 245.70 GWh/yr of electricity, 298.83 GWh/yr of heat, and 185.08 kt/yr of hydrochar. The optimal configuration of the supply chain network, including the selection of supply zones, plant locations and demand locations, transportation links, and mode of transportation is presented, along with the optimal process variables within the plant.
Ključne besede: anaerobic digestion, hydrothermal carbonization, supply chain optimization, process flowsheet optimization, mathematical programming
Objavljeno v DKUM: 07.02.2025; Ogledov: 0; Prenosov: 7
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3. Modeling and optimization of anaerobic digestion technology : current status and future outlookTina Kegl, Eloisa Torres Jiménez, Breda Kegl, Anita Kovač Kralj, Marko Kegl, 2025, pregledni znanstveni članek Ključne besede: renewable energy, anaerobic digestion, biogas plant, mathematical models, optimization algorithms, products utilization
Objavljeno v DKUM: 31.01.2025; Ogledov: 0; Prenosov: 14
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4. Mathematical model-based optimization of trace metal dosage in anaerobic batch bioreactorsTina Kegl, Balasubramanian Paramasivan, Bikash Chandra Maharaj, 2025, izvirni znanstveni članek Opis: Anaerobic digestion (AD) is a promising and yet a complex waste-to-energy technology. To optimize such a process, precise modeling is essential. Developing complex, mechanistically inspired AD models can result in an overwhelming number of parameters that require calibration. This study presents a novel approach that considers the role of trace metals (Ca, K, Mg, Na, Co, Cr, Cu, Fe, Ni, Pb, and Zn) in the modeling, numerical simulation, and optimization of the AD process in a batch bioreactor. In this context, BioModel is enhanced by incorporating the influence of metal activities on chemical, biochemical, and physicochemical processes. Trace metal-related parameters are also included in the calibration of all model parameters. The model’s reliability is rigorously validated by comparing simulation results with experimental data. The study reveals that perturbations of 5% in model parameter values significantly increase the discrepancy between simulated and experimental results up to threefold. Additionally, the study highlights how precise optimization of metal additives can enhance both the quantity and quality of biogas production. The optimal concentrations of trace metals increased biogas and CH4 production by 5.4% and 13.5%, respectively, while H2, H2S, and NH3 decreased by 28.2%, 43.6%, and 42.5%, respectively.
Ključne besede: anaerobic digestion, batch bioreactor, methane production, model parameters calibration, active set optimization method, perturbation of model parameter, gradient based optimization, trace metals
Objavljeno v DKUM: 30.01.2025; Ogledov: 0; Prenosov: 3
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7. Active cellulose acetate/chitosan composite films prepared using solution blow spinning: structure and electrokinetic propertiesAna Kramar, Thomas Luxbacher, Nasrin Moshfeghi Far, Javier González-Benito, 2023, izvirni znanstveni članek Ključne besede: cellulose acetate, chitosan, solution blow spinning, protein adsorption, food packaging
Objavljeno v DKUM: 10.04.2024; Ogledov: 251; Prenosov: 19
Celotno besedilo (4,04 MB)
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8. Solution blow co-spinning of cellulose acetate with poly(ethylene oxide). Structure, morphology, and properties of nanofibersAna Kramar, Thomas Luxbacher, Javier González-Benito, 2023, izvirni znanstveni članek Ključne besede: cellulose acetate, solution blow spinning, co-spinning, zeta potential
Objavljeno v DKUM: 09.04.2024; Ogledov: 163; Prenosov: 22
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9. Ensiling, in vitro rumen digestion and soaking in slurry altered the germination capacity of Rumex obtusifolius seedsAnastazija Gselman, Maksimiljan Brus, 2023, izvirni znanstveni članek Opis: This study investigated whether the process of ensiling and in vitro digestion in rumen juice, as well as the response to soaking in pig or cattle slurry, affects the germination rate and germination energy of Rumex obtusifolius (broad-leaved dock) seeds. Seeds were subjected to different treatments (200 seeds each) in three experiments: (I) seed ensiling (8 weeks) followed by in vitro rumen digestion (24, 36 and 48 h); (II) the soaking of non-ensiled and ensiled seeds in cattle or pig slurry (2, 4 and 24 weeks); and (III) the in vitro rumen digestion (24, 36 and 48 h) of non-ensiled and ensiled seeds followed by soaking in cattle or pig slurry (24 weeks). The control treatment included untreated seed (0—non-ensiled seed; 0—no in vitro rumen digestion; and 0—no soaking in slurry). Germination tests (germination rate and germination energy) were then conducted in four replicates in the germination chamber under alternating day (20–35 °C for 14 h under light) and night conditions (17–20 °C for 10 h without light) at 75% relative humidity. Experiment I showed that ensiling significantly (p ≤ 0.001) reduced both the germination rate and germination energy of R. obtusifolius seeds. In addition, the length of in vitro digestion duration that the non-ensiled seeds were subjected to significantly (p ≤ 0.001) reduced their germination energy but not the total germination rate. However, the seeds that were subjected to the process of ensiling and in vitro digestion in the rumen lost their germination completely. The Experiment II investigated the effects of soaking non-ensiled seeds in slurry and showed that germination rates were comparable in pig and cattle slurry. Longer soaking times significantly reduced the germination rate, with no germination observed after 24 weeks. The Experiment III considered the combined effects of in vitro digestion and slurry soaking and showed that rumen digestion reduced the proportion of germinable seeds. Germination was inhibited in pig slurry, while in cattle slurry, a decreasing germination rate was observed with increasing digestion time.
Ključne besede: broad-leaved dock, in vitro rumen digestion, ensiling, pig and cattle slurry, seed germination
Objavljeno v DKUM: 05.04.2024; Ogledov: 308; Prenosov: 16
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10. Improvement of biogas production utilizing a complex anaerobic digestion model and gradient-based optimizationTina Kegl, Breda Kegl, Marko Kegl, 2024, izvirni znanstveni članek Opis: : Anaerobic digestion (AD) is a promising technology for renewable energy production from organic waste. In order to maximize the produced biogas quantity and quality, this paper deals with the optimization of the AD process in a CSTR bioreactor of a full-scale biogas plant. For this purpose, a novel approach was adopted coupling, a highly complex BioModel for AD simulation, and a gradient-based optimization method. In order to improve AD performance, the dosages of various types of biological additives, the dosages of inorganic additives, and the temperature in the bioreactor were optimized in three different scenarios. The best biogas quality was obtained using multi-objective optimization, where the objective function involves the following two conflicting objectives: the maximization of biogas production and minimization of the needed heating energy. The obtained results show that, potentially, the content of CH4 can be increased by 11%, while the contents of H2, H2S, and NH3 can be reduced by 30%, 20%, and 81% when comparing the simulation results with the experimental data. The obtained results confirm the usefulness of the proposed approach, which can easily be adapted or upgraded for other bioreactor types.
Ključne besede: additives, anaerobic digestion, approximation method, BioModel, complex substrate, gradient-based optimization, process conditions
Objavljeno v DKUM: 12.03.2024; Ogledov: 298; Prenosov: 35
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