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Gomez M.A.,Defense University Center | Porteiro J.,University of Vigo | Patino D.,University of Vigo | Miguez J.L.,University of Vigo
Energy Conversion and Management | Year: 2015

This paper describes a transient model for biomass combustion in a fixed bed boiler. This method implements several submodels which address a variety of conversion processes and interactions between solid and gas phases. A set of Eulerian variables will be defined representing the solid phase state as well as the governing equation model for both the evolution and the thermal conversion of the bed. The solid phase components including the ash content is divided into solid and volatile elements. The fuel feeding is modelled by an advective flux term in the transport equations of the solid phase variables. The advective flux term includes a treatment that prevents the numerical diffusion beyond the bed's surface. This method also includes heat and mass transfer models between phases, particle and bed shrinkage, porous media and gas reactions. Several experimental tests have been simulated to contrast model behaviour. The primary variable profiles of the solid phase in the bed and gas phase in the furnace have been analysed. The results show reasonably good predictions for the exchanged heat and the flue gas concentrations. © 2015 Elsevier Ltd. All rights reserved.

Cancela A.,University of Vigo | Sanchez A.,University of Vigo | Maceiras R.,Defense University Center
European Journal of Engineering Education | Year: 2012

Nowadays, universities tend to promote more learner-centred learning, creating a more interactive and motivational environment for students and teachers. This paper describes an expanded framework to help chemical educators to construct a quiz for solution of chemical exercises in their courses. The novelty of this contribution is that the proposed tool combines a flashcards-based method with knowledge pills. The framework has three levels: definition of problem for a teacher; the quiz; use of the quiz for the student. The tool could provide predefined or automatically generated exercises of chemicals. Students could practise where and whenever they like via the Internet. Theirs answers would be registered automatically by the tool and if the students have doubts about any of the questions, they can see a knowledge pill with a teacher explanation about the solution of the exercise. Moreover, they would be able to check their scores from the tests. Once the flashcards were designed and produced, the opinions of other lecturers and students about them were considered. Both groups considered that the tool could be useful to improve the students' learning process. For future work, this design will be used with the students and its effectiveness will be analysed. © 2012 Copyright Taylor and Francis Group, LLC.

Gomez M.A.,Defense University Center | Porteiro J.,University of Vigo | de la Cuesta D.,University of Vigo | Patino D.,University of Vigo | Miguez J.L.,University of Vigo
Fuel | Year: 2015

This paper presents a transient model for the simulation of biomass combustion in a fixed bed boiler fed through particle drop. The method combines classical CFD techniques, which are used to simulate the gas phase, with a set of Eulerian variables defined to model the solid phase and Lagrangian trajectories that model the particle drop. Several submodels are implemented to simulate the numerous processes that occur during the combustion of the solid phase. These submodels include the thermal conversion of biomass, heat and mass transfer, particle shrinkage and bed compaction as well as the interaction of the DPM (Discrete Phase Model) trajectories and the bed variables. The predictions are contrasted with various experimental tests, which provide reasonably good results and demonstrate the overall good behavior of the models. The simulation facilitates an understanding of the heat transfer inside the boiler and the instability of the emission measurements. © 2015 Elsevier Ltd.

Suarez-Garcia A.,Defense University Center | Alfonsin V.,Defense University Center | Urrejola S.,Defense University Center | Sanchez A.,University of Vigo
Journal of Power Sources | Year: 2015

This paper describes the mathematical parametrization of an electrodynamical battery model using different model selection criteria. A good modeling technique is needed by the battery management units in order to increase battery lifetime. The elements of battery models can be mathematically parametrized to enhance their implementation in simulation environments. In this work, the best mathematical parametrizations are selected using three model selection criteria: the coefficient of determination (R2), the Akaike Information Criterion (AIC) and the Bayes Information Criterion (BIC). The R2 criterion only takes into account the error of the mathematical parametrizations, whereas AIC and BIC consider complexity. A commercial 40 Ah lithium iron phosphate (LiFePO4) battery is modeled and then simulated for contrasting. The OpenModelica open-source modeling and simulation environment is used for doing the battery simulations. The mean percent error of the simulations is 0.0985% for the models parametrized with R2, 0.2300% for the AIC ones, and 0.3756% for the BIC ones. As expected, the R2 selected the most precise, complex and slowest mathematical parametrizations. The AIC criterion chose parametrizations with similar accuracy, but simpler and faster than the R2 ones. © 2015 Elsevier B.V.

Rey G.,Defense University Center | Ulloa C.,Defense University Center | Miguez J.L.,University of Vigo | Arce E.,Defense University Center
Energies | Year: 2016

Micro combined heating and power (micro-CHP) systems are becoming more than important, and even essential, if we pretend to take full advantage of available energy. The efficiency of this kind of systems reaches 90% and important savings in energy transport processes can occur. In this research, an internal combustion engine (ICE)-based micro-CHP system was developed and tested under specific constraints. The system uses a two cylinder Otto engine as prime mover, coupled to an electrical alternator, and it uses exhaust gases and engine cooling circuit heat. The micro-CHP system was developed to match the electrical power of a typical Stirling engine (SE)-based micro-CHP unit, in order to later compare both systems' performance under similar circumstances. Different operating modes were tested under different engine speeds, in order to find the optimum operating point. A stand-alone portable application of this system was performed using recreational sailing boats as mobile homes. Specific considerations had to be taken, related to boundary conditions with sea water, and a transient simulation was performed, considering the boat under three different European climates. Results were compared for the different locations and the performance of the equipment shown. A comparative study with the SE-based micro-CHP system performance was done, and a sensitivity analysis of the influence of the battery size was carried out under the same conditions. The SE and ICE-based proposed micro-CHP system have similar behavior, except for the differences found due to the electric/thermal power ratios in both systems. Battery bank size sensitivity analysis reflects a limit in performance improvement. This limit is caused by the uniform distribution of electrical demand profile. © 2016 by the authors.

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