Video corrections of undergraduate teaching lab reports

Comunicació presentada a INTED2019, 13th International Technology, Education and Development Conference. (March 11-13, 2019, Valencia, Spain).Here it is presented a new methodology based on using video recordings for the evaluation and marking of lab reports in the undergraduate teaching labs. Students are typically requested these reports at each lab session. The reports are partly (or fully) used for the determination of the students mark related to the teaching labs. These reports do not always have the quality expected, since undergraduate students frequently experience different difficulties. Video recordings of the marking process of the reports, with the inclusion of a detailed identification and explanation of the mistakes found, have been performed for the Materials Technology subject in the 4th course of the Industrial Technology Engineering degree. These video recordings, unlike the typically adopted corrections using text comments, were more warmly welcomed by the students, increased the comprehension of the mistakes they performed, and helped them to learn how to prepare higher quality reports. In addition, most of the students considered that these video corrections should be generally implemented in all the teaching labs. Finally, it was also found that marking through this method saves a significant amount of marking time to the lecture

Applications of impedance spectroscopy in thermoelectricity

t is widely used in a lot of different fields (solar cells, fuel cells, corrosion, supercapacitors, batteries, etc.). • Powerful and very reliable equipment are available in the market. • It allows the separation of the physical processes occurring in a device

Low Frequency Impedance Spectroscopy Analysis of Thermoelectric Modules

Impedance spectroscopy is a well-established technique for the study of semiconductors and energy-related devices. However, in the area of thermo- electrics (TEs), this technique is not frequently used and there is a lack of a physical background for a proper interpretation of the results. Usually, in the low frequency regime, the impedance spectrum of TE modules working in cooling mode is characterized by a semicircle which can be modelled as a parallel connection of a resistor and a capacitor. Here, we present a theoretical analysis to understand the origin of both parameters in bulk TE modules working as Peltier coolers. The analysis introduces a thermoelectric capaci- tance and a thermoelectric resistance that are defined by the temperature, the Seebeck coefficient and the thermal properties of the module (specific heat and thermal conductivity, respectively). The product of both provides a time con- stant that directly relates to the thermal diffusivity. Our analysis provides a theoretical model able to interpret the low frequency results and obtain rele- vant thermal parameters from a single impedance measurement.The authors wish to acknowledge financial sup- port from the Accelerated Metallurgy Project, which is co-funded by the European Commission in the 7th Framework Programme (contract NMP4-LA-2011- 263206), by the European Space Agency and by the individual partner organizations. Dr. Upul Wija- yantha and Dr. Matt Carnie are gratefully acknowledged for kindly allowing taking some ini- tial measurements in their laboratories. We thank European Thermodynamics Ltd. for providing the TE module used and Ahmad Akbari R. for mathe- matical support

A novel vacuum pressure sensor using a thermoelectric device

We present the proof-of-concept of a new vacuum pressure sensor based on a new operating principle. The new sensor is formed by the simple combination of a thermoelectric (TE) module that is contacted at both sides by a bent copper plate. The vacuum pressure is related to the change in the thermal contact resistance that exists between the outer ceramic surfaces of the TE module and the copper plate, since heat transfer through the ceramic/copper interface is found to be influenced by the amount of air present in the interface gaps (vacuum pressure). The variations of the thermal contact resistance produce a change of the TE module voltage when a fixed current is applied to it. By monitoring this voltage simultaneously to the response of a commercial pressure sensor at different vacuum pressures inside a vacuum chamber, a calibration equation was identified, which enables obtaining the vacuum pressure from the voltage signal. Random errors lower than 10% were found in the 0.1 to 250 mbar range, which is the pressure range that the sensor can properly sense. This new device is inexpensive, simple to fabricate and integrate, and benefits from the high stability of TE modules

Impedance Spectroscopy Analysis of a Thermo-Electrochemical Cell Under Operating Conditions

Proceedings from the 2022 International Workshop on Impedance Spectroscopy (IWIS), Chemnitz, Germany, 2022.Low-grade (<200°C) heat is an abundant and available energy not generally exploited. In this regard, the so-called thermo-electrochemical cells have become a valid opportunity to harvest this ubiquitous source of heat. They are capable to convert heat into electricity by means of the temperature-redox potential dependency of a redox couple. In fact, they present Seebeck coefficient values in order of mV/K, much higher than solid-state thermoelectrics. In this work, a system formed by two Pt electrodes in contact with a 0.4 M ferro/ferricyanide aqueous solution has been studied by means of impedance spectroscopy under operating conditions (ΔT=40 K). The main processes which govern the performance of the system have been identified, which lead to different resistances: (i) electrolyte ionic resistance, (ii) charge transfer resistance and (iii) mass transfer resistance. It was also demonstrated that the current-voltage characteristics of the device can be obtained knowing the open-circuit potential and performing a single impedance spectroscopy measurement, which determines the device dc resistance. This method can save a significant amount of time in many cases

Impedance Spectroscopy Analysis of Thermoelectric Modules Fabricated with Metallic Outer External Layers

In recent years, thermoelectric (TE) devices have been used in several refrigeration applications and have gained attention for energy generation. To continue the development of devices with higher efficiency, it is necessary not only to characterize their materials but also to optimize device parameters (e.g., thermal contacts). One attempt to increase the efficiency at the device level consists of the replacement of the typical ceramic layers in TE modules by metallic plates, which have higher thermal conductivity. However, this alternative device design requires the use of a very thin electrical insulating layer between the metallic strips that connect the TE legs and the outer external layers, which introduces an additional thermal resistance. Impedance spectroscopy has been proved to be useful to achieve a detailed characterization of TE modules, being even capable to determine the internal thermal contact resistances of the device. For this reason, we use here the impedance method to analyze the device physics of these TE modules with outer metallic plates. We show for the first time that the impedance technique is able to quantify the thermal contact resistances between the metallic strips and the outer layers, which is very challenging for other techniques. Finally, we discuss from our analysis the prospects of using TE modules with external metallic plates.Funding for open access charge: CRUE-Universitat Jaume

Large power factor improvement in a thermoelectric oxide using liquid electrolytes

Comunicació presentada a Conference on Modern Concepts and New Materials for Thermoelectricity (11-15 Mar 2019, Trieste (Italy))• A new hybrid system formed by a nanostructured mesoporous solid permeated by a liquid electrolyte has been conceived to improve the thermoelectric power factor. • The concept has been demonstrated employing Sb:SnO2 and different electrolytes. • More than 3 times improvement in the power factor has been achieved by a 61.9 % reduction of the electric resistance of the system without modifying the Seebeck coefficient using LiBF4 1 M in 3-methoxipropionitrile. • An imidazolium iodide ionic liquid produces an 82.5 % drop in the electric resistance although with a reduction in the Seebeck coefficient, leading to 2.4 times improvement in the PF

Flipped classroom evaluation using kahott and moodle in the undergraduate teaching lab

Comunicación presentada en EDULEARN 2018, 10th International Conference on Education and New Learning Technologies (July 2-4, 2018, Palma, Mallorca, Spain).This article analyzes the implementation of a flipped classroom methodology in the undergraduate teaching labs of engineering degrees. The methodology is focused on providing the students, before the lab session, with audio-visual resources that cover the theoretical background and explanations needed to follow the session. At the beginning of each lab session, the preparatory work performed by the students is evaluated with an on-line test, which was performed using Kahoot and Moodle resources and has an impact on the mark of the session. This methodology is helpful in the sense that eliminates the frequently required theoretical introduction, allowing devoting more time to the experimental part. On the other hand, it provides an immediate information of the degree of prior knowledge gained by the students, so the weaker aspects can be reinforced during the lab session. An analysis of the advantages and disadvantages found for the two on-line resources employed, in conjunction with the impact produced on the students by the methodology is presented. Moodle was found to show greater seriousness and more versatility to introduce the test questions. However, the use of Kahoot was preferred by the students, since it creates a more relaxed lab atmosphere, which was also very useful to increase the participation of some students who were unmotivated. The students recognized that the methodology helped to better follow the lab sessions and improved the quality of their lab reports, which are the items used for their evaluation

Comprehensive impedance spectroscopy equivalent circuit of a thermoelectric device which includes the internal thermal contact resistances

Thermoelectric devices are widely used as solid-state refrigerators and have potential energy generation appli-cations. Their characterization is key to develop more efficient devices and monitor their performance. Electrical impedance spectroscopy has been proved to be a useful method for the characterization of thermoelectric modules. However, deviations from current impedance models still exist in experimental results, especially in the high frequency part of the impedance spectrum, which limits its use. Here, we present a new comprehensive impedance model (equivalent circuit) which covers all the key phenomena that affects the module performance, and it is able to explain the observed deviations. The new equivalent circuit includes, as new additions, the thermal influence of the metallic strips (electrodes), combined with the thermal contact resistance between the metallic strips and the outer ceramic layer. Moreover, a new more accurate spreading-constriction impedance element, which considers the variation of the heat flow in the radial direction at the outer ceramic surfaces, is also developed. The comprehensive equivalent circuit was used to perform fittings to impedance spectroscopy measurements of modules fabricated by different manufacturers. From the fittings, it was possible to identify, among other key properties, the internal thermal contact resistances, whose direct determination is very chal-lenging. Thermal contact resistivities at the metallic strips/thermoelectric elements interface in the range 2.20 ×10-6-1.26 ×10-5 m2KW 1 were found. An excellent thermal contact was identified at the metallic strips/ceramic layers. This opens up the possibility of using impedance spectroscopy as a powerful tool to evaluate, monitor, and identify issues in thermoelectric devices.Funding for open access charge: CRUE-Universitat Jaume

Evaluation of Thermoelectric Generators by I-V Curves

A recent theoretical study proposes a new way to evaluate thermoelectric devices by measuring two I–V curves—one obtained under a constant temperature difference and the other obtained for a constant thermal input. We report an experimental demonstration of the feasibility of this novel technique. A measurement system was designed and constructed, which enables both types of I–V curves to be obtained automatically. The effective ZT values of a thermoelectric module were determined using this system and compared with those measured by an impedance spectroscopy technique. The results confirm the validity of the proposed technique. In addition, the capability of measuring ZT under a large temperature difference was also investigated. The results show that the ZTs obtained for a large temperature difference are significantly smaller than those for a small temperature difference, providing insights into the design and operation of thermoelectric modules in realistic applications.The work is financially supported by the European Commission Research Fund for Coal and Steel programme under the Therelexpro project (RPS-PR-12068) and Globasol project (309194)