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A computational fluid dynamics study is carried out to model the effects of distributed roughness at the airfoil leading-edge using the equivalent sand grain approach and Reynolds-averaged Navier–Stokes equations. The turbulence model k−ω−shear stress transport (SST) is selected to emulate a fully turbulent flow. Three k and ω boundary conditions are studied to model roughness effects. One refers to Wilcox's boundary condition and the other two refer to Aupoix's boundary conditions. Besides, Hellsten's correction is used to ensure Wilcox's boundary condition compatibility with the shear stress transport limiter. After validating the implementation of these boundary conditions, they are applied to three different airfoils. One of them is a thick airfoil with industrial relevance. For this airfoil, Wilcox's boundary condition significantly underestimates the roughness impact on aerodynamic coefficients. The pressure gradient simplification in Wilcox's boundary condition formulation is the driving factor behind this effect. The pressure gradient effect on Aupoix's boundary condition is minimal.

The nowadays European educational framework boosts applying the learned theoretical concepts to real situations. Hence, practice sessions are key resources to present students direct applications of the theoretical concepts shown in class. Thus, developing new educational equipment and practice sessions oriented to bringing theoretical knowledge closer to practice should be one of the objectives of teachers. The present work describes a solution proposed by lectures of two Spanish universities looking to increase the knowledge of their engineering students. Along the years, these docents have noticed the lack of connection between the theoretical and practical knowledge among their students, drastically harming their learning procedure. Thus, in order to deepen into practical learning, a teaching methodology involving low-cost prototypes of vapor compression systems and a gamification method to help the students understand the concepts is proposed. The proposed methodology is expected to make a big positive impact on the results obtained by the students, taking into account the preliminary results reached. The authors are indebted to the Spanish Ministry of Science, Innovation and Universities, and European Regional Development Fund for the economic support to this work, included in the RTI2018-093501-B-C21 and RTI2018-093501-B-C22 research projects and to the Public University of Navarre for the economic support to this work included in the PJUPNA2003 research project.

To improve the performance of vapour compression refrigeration cycles, the inclusion of a thermoelectric subcooler for low-medium power units has been the focus of recent studies due to its robustness, compactness and simplicity of operation. In thermoelectric systems, it has been demonstrated that the heat exchangers used in the hot and cold side of the thermoelectric modules have a critical impact in the performance of the system. This influence has not yet been studied for thermoelectric subcooling systems in vapour compression cycles. This work, for the first time, evaluates the impact that the heat exchangers of a thermoelectric subcooler, included in a transcritical carbon dioxide refrigeration cycle, have, in the performance of the refrigeration cycle. The influence is quantified in terms of: optimum working conditions, coefficient of performance and cooling capacity. The results show that, through an optimization of the heat exchangers of the thermoelectric subcooler, the performance improvements on the coefficient of performance using this technology are boosted from 11.96 to 14.75 % and the upgrade in the cooling capacity of the system rises from 21.4 to 26.3 %. Moreover, the optimum gas-cooler working pressure of the system is reduced and the optimum voltage supplied to the thermoelectric modules increases. The authors would like to acknowledge the support of the Spanish Ministry of Science, Innovation and Universities, and European Regional Development Fund, for the funding under the RTI2018-093501-B-C21 and RTI2018-093501-B-C22 research projects. We would also like to acknowledge the support from the Education Department of the Government of Navarra with the Predoctoral Grants for Phd programmes of Interest to Navarra and the Official School of Industrial Engineers of Navarre with the scholarship Fuentes Dutor. Open access funding provided by Universidad Pública de Navarra.

The use of thermoelectric heat pumps for heat, ventilation, and air conditioning in nearly-zero-energy buildings is one of the most promising applications of thermoelectrics. However, simulation works in the literature are predominately based on the simple model, which was proven to exhibit significant deviations from experimental results. Nine modelling techniques have been compared in this work, according to statistical methods based on uncertainty analysis, in terms of predicted coefficient of performance and cooling power. These techniques come from the combination of three simulation models for thermoelectric modules (simple model, improved model, electric analogy) and five methods for implementing the thermoelectric properties. The main conclusion is that there is no statistical difference in the mean values of coefficient of performance and cooling power provided by these modelling techniques under all the scenarios, at 95% level of confidence. However, differences appear in the precision of these results in terms of uncertainty of the confidence intervals. Minimum values of uncertainty are obtained when the thermal resistance ratio approaches 0.1, being ±8% when using temperature-dependent expressions for the thermoelectric properties, ±18% when using Lineykin’s method, and ± 25% when using Chen’s method. The best combination is that composed of the simple model and temperature-dependent expressions for the thermoelectric properties. Additionally, if low values of resistance ratio are anticipated, empirical expressions from the literature can be used for the thermal resistance of the heat exchangers; for high values, though, experimental tests should be deployed, especially for the heat exchanger on the hot side.

This paper makes evident that a rigorous review of simulation methods for thermoelectric heat pumps in nearly-zero energy buildings is needed, as incoherent results during verification and validation of simulation models are reported in the literature. Statistical methods based on uncertainty analysis are deployed to calculate the minimum deviations between experimental and simulated values of the main variables that define the performance of a thermoelectric heat pump, within working scenarios expected in nearly-zero energy buildings. Results indicate that the narrower confidence intervals of these deviations are set by the uncertainties in the calculation of the thermoelecric properties of the thermoelectric modules. The minimum deviation in the prediction of the electric power consumed by the thermoelectric heat pump is ±6% in all scenarios. Likewise, confidence intervals for the heat flow emitted to the hot reservoir range from ±8% for high operating voltages of the thermoelectric heat pump to ±23% for low ones. In similar terms, those of the coefficient of performance range from ±4% to ±21%. These lower limits cannot be reduced unless the uncertainties in the measurement of the thermoelectric properties are reduced. In fact, these confidence intervals are due to increase as more uncertainties are added in the analysis, so wider intervals are expected when heat exchangers and complex heat reservoir are introduced in the system. To avoid so, several guidelines for uncertainty reduction are included in the paper, intended to increase the reliability of the simulation of thermoelectric heat pumps. Among them, relevant is the precise account of the aspect ratio in a thermoelectric module, as well as the deployment of temperature and voltage sensors with systematic standard uncertainties lower than 0.3 °C and 0.01 V respectively. The paper demonstrates the relevance of uncertainty propagation analysis in the verification and validation of the simulation models in this field, and underlines how misleading could be just to compare average values of experimental and simulated results. This work was supported by the Spanish Ministry of Science, Innovation and Universities [grant number RTI2018-093501-B-C22 ].

The refrigeration process reduces the temperature of a space or a given volume while the power generation process employs a source of thermal energy to generate electrical power. Because of the importance of these two processes, training of engineers in this area is of great interest. In engineering courses it is normally studied the vapor compression and absorption refrigeration, and power generation systems such as gas turbine and steam turbine. Another type of cooling and generation less studied within the engineering curriculum, having a great interest, it is cooling and thermal generation based on Peltier and Seebeck effects. The theoretical concepts are useful, but students have difficulties understanding the physical meaning of their possible applications. Providing students with tools to test and apply the theory in real applications, will lead to a better understanding of the subject. Engineers must have strong theoretical, computational and also experimental skills. A prototype test bench has been built and experimentally validated to perform practical lessons of thermoelectric generation and refrigeration. Using this prototype students learn the most effective way of cooling systems and thermal power generation as well as basic concepts associated with thermoelectricity. It has been proven that students learn the process of data acquisition, and the technology used in thermoelectric devices. These practical lessons are implemented for a 60 people group of students in the development of subject of Thermodynamic including in the Degree in Engineering in Industrial Technologies of Public University of Navarra.

INVESTIGACIÓN Y FORMACIÓN DOCENTE EN RED: construyendo saberes, experiencias y reflexiones como magister en educación es una colección monográfica de Egresados de la Maestría en Educación de la Universidad Santo Tomás-VUAD que propone a los profesores, maestros, investigadores, estudiantes en el campo de la educación, la pedagogía y la investigación educativa, artículos científicos resultado de investigaciones terminadas, distintas reflexiones teóricas, epistemológicas y prácticas sobre temáticas actuales de la educación en diversos contextos. Se considera que esta Colección permite un acercamiento a la investigación de carácter formativo que se lleva a cabo en la Maestría, siendo esta de gran importancia para fortalecer los procesos investigativos y formativos en educación. La Maestría en Educación tiene como una de sus apuestas investigativas considerar que los discursos, reflexiones y análisis en torno a la educación, deben estar relacionados estrechamente con el trabajo investigativo que desarrollan los maestrantes a lo largo de su formación, ya que estos permiten la construcción de un discurso profundo y en relación con la praxis investigativa. De este modo, los artículos presentes en este ejemplar se convierten en un pretexto para indagar, dialogar, profundizar en el sentido que tiene la educación, la pedagogía y la investigación no solo en el contexto académico, sino en el contexto social, vislumbrando el impacto que producen estas investigaciones en nuestro contexto y el fomento de nuevas alternativas para el desarrollo y mejoramiento de los procesos educativos del país. Igualmente, estos artículos son instrumentos útiles para fundamentar la educación y su significado, y a la vez, se pueden entender como una orientación teórica y práctica del quehacer de los docentes, así como el papel imprescindible que tiene la investigación en todo proceso educativo, otorgando de sentido todo aquello que tenga que ver con el campo de la educación, la investigación y la pedagogía. El material adscrito a esta Colección tiene como destinatarios todos los sectores educativos, con el ánimo que desde estos lugares se promueva la circulación de conocimiento y discusión intelectual, pues el verdadero valor e importancia de esta obra es inquietar a los lectores, en la medida que los convoque en un dialogo permanente y significativo que contribuya a crear ideas renovadas y nuevas posibilidades para pensar y repensar la educación, la pedagogía y la investigación RESEARCH AND TEACHER EDUCATION IN NETWORK: building knowledge, experiences and reflections as a magister in education is a monographic collection of Graduates of the Master of Education at the University Santo Tomás-VUAD that proposes to teachers, teachers, researchers, students in the field of education, pedagogy and educational research, scientific articles resulting from completed research, different theoretical, epistemological and practical reflections on current issues of education in different contexts. It is considered that this Collection allows an approach to the research of a formative nature that is carried out in the Master's, being this of great importance to strengthen the research and educational processes in education. The Master in Education has as one of its investigative bets to consider that the discourses, reflections and analysis around education, should be closely related to the investigative work that the teachers develop throughout their training, since these allow the construction of a deep discourse and in relation to the investigative praxis. In this way, the articles present in this issue become a pretext to investigate, dialogue, deepen the meaning of education, pedagogy and research not only in the academic context, but in the social context, glimpsing the impact that produce these investigations in our context and the promotion of new alternatives for the development and improvement of the educational processes of the country. Likewise, these articles are useful tools to support education and its meaning, and at the same time, can be understood as a theoretical and practical orientation of teachers' work, as well as the indispensable role that research has in every educational process, granting I mean everything that has to do with the field of education, research and pedagogy. The material assigned to this Collection is aimed at all educational sectors, with the encouragement from these places to promote the circulation of knowledge and intellectual discussion, as the true value and importance of this work is to disturb readers, to the extent that convene them in a permanent and meaningful dialogue that contributes to creating renewed ideas and new possibilities to think and rethink education, pedagogy and research