Understanding Uncertainties in Thermographic Imaging

7 p.The present article proposes a workflow based on free/open-source software solutions for the acquisition of competences in engineering courses related to the use of thermographic images. The approach is aimed to three-dimensional visualization techniques over thermographic images to improve the comprehension and interpretation of the different error sources that affects the measurements, and therefore the conclusions and analysis derived from them. The present work is framed inside the virtual laboratories discipline, as the new learning material can be employed for the acquisition of competences and skills. Additionally, it can be used for the evaluation of competences in asynchronous and e-learning programs. The learning materials could be easily deployed in a learning management system, allowing the students to work with the models by means of open-source solutions easily, both in asynchronous and face-to-face courses. Consequently, the present approach will improve the application of professional techniques, so the future professionals will reach the working market better prepared.S

Análisis de la distribución de la temperatura en motores de inducción mediante un modelo híbrido de red térmica de parámetros concentrados y elementos finitos

En el capítulo primero se analiza la importancia del conocimiento de la temperatura de los motores de inducción así como su implicación técnica y económica. También será objeto de estudio, las distintas fuentes de calor en las máquinas eléctricas, su origen, su determinación e inconvenientes que se presentan en la misma. Por último, se realiza un estudio de los modelos térmicos disponibles para su utilización en capítulos posteriores. En el capítulo segundo, basado en los estudios previos, se marcarán los objetivos a conseguir, junto con las actuaciones precisas para alcanzarlos y el material necesario. El capítulo tercero se analiza por separado el campo electromagnético y el térmico, y las interacciones entre ellos. Se estudia las leyes que fundamentan el campo electromagnético, las ecuaciones que lo definen y los métodos para resolverlas. Hasta concluir que, debido a las características geométricas de estas máquinas, el método más adecuado para su resolución aproximada es el método de los elementos finitos. En cuanto al campo térmico, se analizan los mecanismos de transmisión de calor que intervienen en el funcionamiento de las máquinas eléctricas, sus ecuaciones y las dificultades que plantean la determinación de sus parámetros, en especial, en el caso de transmisión de calor por convección. Este capítulo finaliza, con el análisis de la interacción entre ambos campos y la dependencia de todas las propiedades físicas de los materiales, que intervienen en la construcción de esta máquina eléctrica, con la temperatura. La caracterización de los materiales compuestos, será clave en los modelos térmicos posteriores. En el capítulo cuarto se realiza el modelado electromagnético del motor de inducción basado en el método de los elementos finitos. [...

Investigation of the Effect of Albedo in Photovoltaic Systems for Urban Applications: Case Study for Spain

Rooftop photovoltaic generation can help cities become key players in the transition to clean energy. The optimal solar photovoltaic production on rooftops depends on two angles: tilt angle and azimuth angle. It is accepted in all studies that the ideal orientation of photovoltaic modules is toward the south (north) in the northern hemisphere (south). In contrast, the determination of the optimum tilt angle is more complex, and there are different equations for its calculation. Most of these equations do not take albedo into account. In this work, 47 Spanish province capitals representing the most populated cities have been studied with different equations for the calculation of the optimum annual tilt angle (Technical report by the Spanish Institute for the Diversification and Saving of Energy (IDAE), Lorenzo’s and Jacobson’s equation) and different types of albedo. Accounting for the geographical and the meteorological conditions of the cities, we analyzed the optimum tilt angle through a Mathematica© optimization code. The influence that different variables have on optimum tilt angle has been quantified by means of the term relative energy harvested. The use of the equations as a function of latitude increases the annual relative energy harvested by increasing the albedo. When the albedo is 0.2, the annual relative energy harvested is very similar in all equations. Comparing to the method that maximizes the total irradiation incident on a tilted surface, the minimum and maximum value of the percentage of relative energy harvested per year were 0.01 and 2.50% for the IDAE guideline, 0.00 and 2.38% for Lorenzo’s equation, 0.00 and 2.46% for Jacobson’s equation. A simplified polynomial regression model to estimate optimum tilt angle as a function of latitude, altitude and albedo has been proposed as well

A New Two-Foci V-Trough Concentrator for Small-Scale Linear Fresnel Reflectors

We present the design of an original secondary cavity for use in Small-Scale Fresnel Reflectors in photovoltaic applications. The cavity is similar to the classical V-trough, but the primary reflector system is configured so that there are two focal points on the aperture. The rays coming from each side of the primary system reach the opposite side of the cavity, producing a non-symmetrical distribution of the irradiance. This modifies the acceptance half-angle and allows us to break the maximum limit for the concentration ratio of ideal symmetric concentrators. Our study is analytic, and we provide formulas for any number of reflections. Numerical simulations with a ray-tracing program based on MATLAB are included. We provide a comparison of optical concentration ratio, height and cost parameter between our system and two classical designs with a single focal point: the V-trough and the Compound Parabolic concentrators. This way, we verify that our design yields better concentration ratios while keeping the ray acceptance rate at one. Our solution proves to be better than both the classical one-focus V-trough and the Compound Parabolic concentrator. Specifically, the proposed solution is significantly better than the classical one-focus V-trough in optical concentration ratio, with an increase between 15.02 and 35.95%. As regards the compound parabolic concentrator, the optical concentration ratio is always slightly better (around 4%). The height of the cavity, however, is notably less in this design (around 54.33%)

A New Two-Foci V-Trough Concentrator for Small-Scale Linear Fresnel Reflectors

We present the design of an original secondary cavity for use in Small-Scale Fresnel Reflectors in photovoltaic applications. The cavity is similar to the classical V-trough, but the primary reflector system is configured so that there are two focal points on the aperture. The rays coming from each side of the primary system reach the opposite side of the cavity, producing a non-symmetrical distribution of the irradiance. This modifies the acceptance half-angle and allows us to break the maximum limit for the concentration ratio of ideal symmetric concentrators. Our study is analytic, and we provide formulas for any number of reflections. Numerical simulations with a ray-tracing program based on MATLAB are included. We provide a comparison of optical concentration ratio, height and cost parameter between our system and two classical designs with a single focal point: the V-trough and the Compound Parabolic concentrators. This way, we verify that our design yields better concentration ratios while keeping the ray acceptance rate at one. Our solution proves to be better than both the classical one-focus V-trough and the Compound Parabolic concentrator. Specifically, the proposed solution is significantly better than the classical one-focus V-trough in optical concentration ratio, with an increase between 15.02 and 35.95%. As regards the compound parabolic concentrator, the optical concentration ratio is always slightly better (around 4%). The height of the cavity, however, is notably less in this design (around 54.33%)