1. Fast single domain-subdomain BEM algorithm for 3D incompressible fluid flow and heat transferJure Ravnik, Leopold Škerget, Zoran Žunič, 2009, izvirni znanstveni članek Opis: In this paper acceleration and computer memory reduction of an algorithm for the simulation of laminar viscous flows and heat transfer is presented. The algorithm solves the velocity-vorticity formulation of the incompressible Navier-Stokes equations in 3D. It is based on a combination of a subdomain boundary element method (BEM) and single domain BEM. The CPU time and storage requirements of the single domain BEM are reduced by implementing a fast multipole expansion method. The Laplace fundamental solution, which is used as a special weighting function in BEM, is expanded in terms of spherical harmonics. The computational domain and its boundary are recursively cut up forming a tree of clusters of boundary elements and domain cells. Data sparse representation is used in parts of the matrix, which correspond to boundary-domain clusters pairs that are admissible for expansion. Significant reduction of the complexity is achieved. The paper presents results of testing of the multipole expansion algorithm by exploring its effect on the accuracy of the solution and its influence on the non-linear convergence properties of the solver. Two 3D benchmark numerical examples are used: the lid-driven cavity and the onset of natural convection in a differentially heated enclosure. Ključne besede: boundary element method, fast multipole method, fluid flow, heat transfer, velocity-vorticity fomulation Objavljeno: 31.05.2012; Ogledov: 1175; Prenosov: 19 Povezava na celotno besedilo |
2. Heat integration between two biodiesel processes using a simple methodAnita Kovač Kralj, 2008, izvirni znanstveni članek Opis: Biodiesel is a clean-burning alternative fuel, produced from domestic, renewable resources. Biodiesel can be blended at any level with petroleum diesel to create a biodiesel blend. It can be used in compression-ignition (diesel) engines with little or no modification. Biodiesel is simple to use, biodegradable, nontoxic, and essentially free of sulfur and aromatics. This paper presents heat integration between two biodiesel processes. Biodiesel can be produced by the esterification of different fatty acids (high and low boiling point) with alcohols. This simple method for heat integration is based on three possible steps. Simultaneous integration between processes can be performed using a stagewise model with a mixed integer nonlinear programming (MINLP) algorithm (step 3), which can include alternatives suggested by pinch analysis of heat transfer between the processes (step 2). The internal integration of individual processes can be performed in step 1. The fraction can be calculated for maximum integration between processes. Integration between the processes can be carried out using all three steps or by the first and third steps or by the last step only, depending on the problems' complexities. This method includes streams of different processes which are heated or cooled using a utility only. The existing heaters and coolers can be left unchanged in their original processes or can be used for integrating heat between processes, with hot and cold utilities being saved. This approach is illustrated by integrating two simulated biodiesel processes.The objective was to maximize additional annual profit for integration between processes by USD8300/a. Ključne besede: chemical processing, biodiesel producing, heat integration, nonlinear programming Objavljeno: 31.05.2012; Ogledov: 1111; Prenosov: 27 Povezava na celotno besedilo |
3. Influence of water scale on thermal flow losses of domestic appliancesDanijela Urbancl, Darko Goričanec, 2007, izvirni znanstveni članek Opis: Research results of how the precipitated water scale on heaters of small domestic appliances influences the consumption of electricity are presented. It shows that the majority of water scale samples are composed of aragonite, calcite and dolomite and that those components have an extraordinary low thermal conductivity. Also, the results show that at 2 mm thick deposit, depending on the chemical composition of water scale, the thermal flow is reduced for 10% to 40%; consequently, the consumption of electricity significantly increases. Ključne besede: electricity, heat transfer, heat flow, heat exchanger, water scale Objavljeno: 31.05.2012; Ogledov: 1132; Prenosov: 41 Povezava na celotno besedilo |
4. Response functions and thermal influence for various multiple borehole configurations in ground coupled heat pump systemsMetka Pešl, Darko Goričanec, 2007, izvirni znanstveni članek Opis: Ground coupled heat pump (GCHP) utilizes the immense renewable storage capacity of the ground as a heat source or sink to provide space heating, cooling, and domestic hot water. GCHP systems are generally comprised of watersource heat pumps and ground heat exchangers (GHEs). Consisting of closedloop of pipes buried in boreholes, ground heat exchangers (GHEs) are devised for extraction or injection of thermal energy from/into the ground. Despite the low energy and lower maintenance benefits of ground-source heat pump systems, little work has been undertaken in detailed analysis. Many models, either numerical or analytical, have been proposed to analyze the thermal response of vertical heat exchangers that are used in ground coupled heat pump systems (GCHP). In both approaches, most of the models are valid after few hours of operation since they neglect the heat capacity of the borehole. In this paper, we present for three various multiple borehole configurations a comparison between g-functions, which will be calculated after an analytical model of final line source and g-functions, obtain with numerical model derived from the work of Eskilson. A case study is presented to show how the ground temperature changes with time for various multiple borehole configurations. Ključne besede: geothermal heat exchanger, heat transfer, heat conduction, thermal influence Objavljeno: 31.05.2012; Ogledov: 1036; Prenosov: 22 Povezava na celotno besedilo |
5. Economic analysis of geothermal heat source for residential area projectSašo Poberžnik, Darko Goričanec, Jurij Krope, 2007, izvirni znanstveni članek Opis: The article discusses the economic analysis of heat source for residential area project. The energy source is geothermal energy. Every house has its own borehole heat exchanger (BHE) and heat pump in basement. In this system low temperature floor and wall heating was carried out. The economic analysis was performed as a pilot study for real system with all installation needed to runthe system. The analysis has been done using the method of the net present value. In the research the coefficient of profitability and the period of timein which the investment is going to return itself were established. The system has been compared to the conventional system that uses fossil fuel (Liquidized naphtha gas- LNG) to heat the building and domestic hot water. Ključne besede: geothermal heat, area projects, borehole heat exchanger, economic analysis Objavljeno: 31.05.2012; Ogledov: 931; Prenosov: 23 Povezava na celotno besedilo |
6. Heat integration in a speciality product processMajda Krajnc, Anita Kovač Kralj, Peter Glavič, 2006, izvirni znanstveni članek Opis: The essence of effective process designing is to use methods which are efficient to engineers in practice and not only to scientists. The proposed design procedure is composed of two steps: conceptual one and optimization one. At the conceptual step, pinch design analysis is used. In the optimization step pinch analysis and mixed-integer nonlinear programming method are applied. In the case study analysed, a speciality product is to beproduced in continuous chemical process with a capacity which causes smallerheat flow rates and needs smaller heat exchanger areas than usual. Therefore, an equation for cost estimation of heat exchangers with areas smaller than 7 m2 was developed and used in the optimization procedure. Using thermodynamic pinch analysis and mathematical programming method, the heat integrated structures were synthesized and compared with the base process flowsheet. Finally, the optimal structure was determined. Ključne besede: načrtovanje procesov, načrtovanje procesov, ekonomska analiza, prenos toplote, optimizacija, chemical process design, economic analysis, heat integration, optimization Objavljeno: 30.05.2012; Ogledov: 1301; Prenosov: 11 Povezava na celotno besedilo |
7. Design of the optimal total site heat recovery system using SSSP approachAndreja Goršek, Peter Glavič, Miloš Bogataj, 2006, izvirni znanstveni članek Opis: Site expansions or changes in production capacities are usually related with changes of utilities demands andžor utility system design. Despite several available and well established techniques for process synthesis and integration, very often, changes in process designs are made on the basis of intuition and experiences of engineers. In this paper possibilities of rational energy consumption and energy integration in an existing site for production of specialty chemicals were studied. On the basis of real process parameters and computer simulation results energy integration was re-examined.Total site analysis using modified Site Sink Source Profiles, which gives a profound insight into the site utility system configuration, heating-cooling demands and cogeneration design was performed. The existing site was found to be very well designed. With only few modifications additional 9% of hot utilities and 5% of cold utilities savings are possible. Ključne besede: chemical engineering, process design, optimization, heat integration, cogeneration, pinch method, energy retrofit Objavljeno: 30.05.2012; Ogledov: 1634; Prenosov: 32 Povezava na celotno besedilo |
8. Modelling and parameter comparison of equivalent circuits on the basis of impedance measurements of stainless steelsMojca Slemnik, 2006, izvirni znanstveni članek Opis: In our former work [1] we have discussed the impedance of differently heat treated steels X20Cr13 in 0.1 M H2SO4, undergoing an active passive transition. Impedance spectra were interpreted in terms of a model by Armstrong [2, 3], describing the electrochemical reaction at interfaces with adsorbed intermediates. The present work was performed in order to study this phenomenon in more detail, with computer simulations of a new created and more convenient equivalent circuit in comparison with the former model. Computer simulations of equivalent circuits were also made in the region of passivity which was also continuation of our earlier work [4]. In this sense the entire study for these steels was completed by collating distinctive parameter values, demonstrating electrochemical characteristics of steel X20Cr13, undergoing different heat treatments in the active-passive and passive region. Ključne besede: electrochemical impedance spectroscopy, equivalent circuits, stainless steel, heat treatment of steel Objavljeno: 30.05.2012; Ogledov: 1025; Prenosov: 21 Povezava na celotno besedilo |
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10. H2 separation and use in fuel cells and CO2 separation and reuse as a reactant in the existing methanol processAnita Kovač Kralj, Peter Glavič, 2007, izvirni znanstveni članek Opis: Fuel-cell efficiencies yield substantial reductions in the emissions of climate-change gases and promise an end to exclusive reliance on carbon fuels for energy. Fuel cells, CO2 reuse, process heat integration, and open gas turbine electricity cogeneration can be optimized simultaneously, using a nonlinear programming (NLP) algorithm. The simplified NLP model contains equations of structural and parametric optimization. This NLP model is used tooptimize complex and energy-intensive continuous processes. This procedure does not guarantee a global cost optimum, but it does lead to good, perhaps near-optimum, designs. The plant, which produces methanol, has a surplus of hydrogen (H2) and CO2 flow rates in purge gas. H2 is separated from the purge gas by an existing pressure swing adsorption (PSA) column. Pure H2 can be usedas fuel in fuel cells. CO2 can be separated from the outlet stream (purge gas) by a membrane or absorption system (absorber and regenerator) or an adsorption system and reused as a reactant in a reactor system. Therefore, theproduct yield can be increased and CO2 emissions can be reduced, simultaneously. CO2 emissions can then be reduced at the source. The retrofitted process can be operated within existing parameters. Using a methanol process as a case study, the CO2 emission flow rate can be reduced by4800 t/a. The additional electricity cogeneration in the gas turbine and in fuel cells and additional flow rates of the raw material could generate an additional profit of 2.54 MEUR/a. Ključne besede: chemical processing, methanol production, optimization, nonlinear programming, CO2 reuse, fuel cells, heat integration, energy cogeneration Objavljeno: 31.05.2012; Ogledov: 1450; Prenosov: 29 Povezava na celotno besedilo |