Defense University Center

Naval Academy, Spain

Defense University Center

Naval Academy, Spain

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Maceiras R.,Defense University Center | Alfonsin V.,Defense University Center
Environmental Progress and Sustainable Energy | Year: 2016

The use of microalgal lipids for liquid fuels production is an emerging alternative. Before extracting lipids from microalgae, some important stages are necessary such as: microalgae dewatering and lipids extraction. The cultivation of microalgae is made in a great amount of water, then it is necessary the use of water removal techniques before the lipids extraction. Furthermore, lipids extraction techniques must be tuned up in order to achieve a better separation depending on the type of technique and the solvent. The purpose of the present study is to compare two different microalgae harvesting techniques and two methods for the total lipids extraction of Pavlova-Lutheri microalgae. The studied harvesting techniques for microalgae recovery were: flocculation-coagulation (99.8% efficiency) and electrocoagulation (97.4% efficiency). Two extraction methods were also studied with different solvents: Soxhlet and ultrasound. It was observed that, the use of ultrasound irradiation for lipids extraction improves the extraction efficiency. In ultrasound extraction, the highest percentage (47.20%) was reached with a mixture of chloroform and methanol 1:2 as extraction solvent. © 2016 American Institute of Chemical Engineers Environ Prog.

Porteiro J.,University of Vigo | Miguez J.L.,University of Vigo | Crespo B.,University of Vigo | De Lara J.,Technical University of Madrid | Pousada J.M.,Defense University Center
Materials | Year: 2016

Advantages, such as thermal storage improvement, are found when using PCMs (Phase Change Materials) in storage tanks. The inclusion of three different types of materials in a 60 ℓ test tank is studied. Two test methodologies were developed, and four tests were performed following each methodology. A thermal analysis is performed to check the thermal properties of each PCM. The distributions of the water temperatures inside the test tanks are evaluated by installing four Pt-100 sensors at different heights. A temperature recovery is observed after exposing the test tank to an energy demand. An energetic analysis that takes into account the energy due to the water temperature, the energy due to the PCM and the thermal loss to the ambient environment is also presented. The percentage of each PCM that remains in the liquid state after the energy demand is obtained. © 2016 by the authors.

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.

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: 2016

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

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.

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.

Alfonsin V.,Defense University Center | Suarez A.,Defense University Center | Urrejola S.,Defense University Center | Miguez J.,University of Vigo | Sanchez A.,University of Vigo
International Journal of Hydrogen Energy | Year: 2015

This paper presents the technical study of a commercial sailboat conversion, originally manufactured with an internal combustion engine (ICE), into electrical hybrid propulsion system with fuel cell and batteries. Batteries are charged with electrical energy from grid when boat remains at port. The used hydrogen is generated with the electrolysis of water using energy provided through the on-board renewable system (eolic, photovoltaic and marine generation). In order to check the viability of conversion mathematical modelling is used. Firstly, hull hydrodynamic resistance is obtained through Free!Ship software. Then, this result is implemented into a global model which is developed under Matlab/Simulink® environment. Furthermore, renewable energy and power systems are developed as Simulink® models and a logic controller manages them. In this study, the selection of all energy and power elements is shown. Real operation sailboat under real conditions is simulated. Finally, results obtained are compared with Spanish Navigation Normative to study a possible technical feasibility. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Prego F.J.,University of Vigo | Solla M.,Defense University Center | Nunez-Nieto X.,Defense University Center | Arias P.,University of Vigo
Journal of Construction Engineering and Management | Year: 2016

Ground-penetrating radar (GPR) has proved to be a valuable method for tunneling quality management and evaluation. The research literature includes many successful works addressing the use of this technique with the aim to detect the existence of internal pathologies and anomalies. However, most of them have been carried out on tunnels in operation. In these situations, the identification of inner elements and possible damage has been severely limited due to a shallower rebar mesh that complicates the radar data interpretation process. Therefore, this paper presents the evaluation of an excavated high-speed railway tunnel during the early stages of construction instead of considering a finished one. The purpose of the study was to demonstrate the potential of this method when applied during these first critical phases. The results provided noteworthy information: namely, thickness of the gunite layer, lining voids and delamination, moisture problems, and the presence of reinforcing in the tunnel lining. All this information may be useful for civil engineers when they must make a decision on maintenance and prevention tasks. © 2015 American Society of Civil Engineers.

Perez L.,University of Vigo | Salgueiro J.L.,University of Vigo | Maceiras R.,Defense University Center | Cancela A.,University of Vigo | Sanchez A.,University of Vigo
Chemical Engineering and Technology | Year: 2016

Harvesting is one of the most important operations in microalgal biomass utilization. Two types of flocculants are widely used in flocculation. Inorganic flocculants are usually cheaper than organic flocculants, but leave more contaminants on the culture media. The combination of one inorganic and one organic flocculant and its synergy for the marine microalgae Chaetoceros gracilis harvesting process is reported. The efficiency of eight inorganic and five organic flocculants was studied. The results show that, when only FeCl3 was used, high doses were required for high levels of biomass recovery, whereas chitosan alone led to poor recoveries. However, when both flocculants were used in combined flocculation, total biomass recovery was achieved, even at low doses. Copyright © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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