Real-time monitoring of ground-tire rubber microwave devulcanization with thermal and electrochemical sensors

Devulcanizing ground-tire rubber (GTR) properly requires the removal of the sulphur linkages that crosslink the polymer. The volatile sulphur compounds (VSCs) released during the process must be extracted from the reactor to avoid any chemical recombination, and the sulphur gas concentrations conveniently sensed during the extraction, along with a thermal sensoring of the payload, can be used to monitor the whole devulcanization process. In this contribution, a modified conventional microwave oven was used to devulcanize the GTR. The microwave-processed GTR was evaluated by determining the values of its mass loss (ML), soluble fraction (sol fraction), and the variation of its electric permittivity. Results show a direct relationship between the energy delivered, sol fraction, the VSCs concentrations, the ML, and the permittivity values. Thus, this paper demonstrates that monitoring the VSCs can provide a reliable indication of ML and, consequently, devulcanization evolution even at non-uniform temperature conditions

A low-cost robust configuration for the temperature monitoring within the payload of any microwave oven with a rotating turntable

This contribution aims to be a reference to help researchers build up their own microwave heating systems for monitoring the temperature evolution of a payload with almost endlessly (limited by the batteries capacity of the measuring system) rotational movements. Its robustness is because it allows keeping sensors in place thus avoiding the fiber optics wringing/twisting while the payload is rotating. The proposed system facilitates the rotation of the temperature equipment located over the microwave oven synchronously with the payload, while its data is transferred in real time by an RF transmitter/receiver device connected to its serial data port. The fiber optic sensors deployed from the temperature equipment ports to the measuring points are arranged with the rotation axis through a hollowed shaft to minimize mechanical stresses. The equipment operation, its configuration, and the data transmissions are controlled wirelessly by a laptop computer. The prototype presented in this paper was implemented for a total budget amount of 6500 €

Assembly flowshop scheduling problem: Speed-up procedure and computational evaluation

In this paper, we address the assembly flowshop scheduling problem, which is a generalisation of two well-known scheduling problems in the literature: the three-stage Assembly Scheduling Problem (ASP) and its variant with two stages denoted as the two-stage ASP. For this problem, we prove several theoretical results which are used to propose a speed-up procedure. This acceleration mechanism can be applied in any insertion-based method for the problem under study and, consequently, also for their special cases. In addition, we propose four efficient constructive heuristics for the problem, based on both Johnson’s algorithm and the NEH heuristic. These proposals are compared against 47 algorithms existing in the literature for related problems. The results show the excellent performance of the proposals.Ministerio de Ciencia e Innovación PID2019-108756RB-I00Junta de Andalucía P18-FR-1149, 5835Junta de Andalucía US- 126451

Low-cost setup for the characterizacion of the dielectric properties of materials versus temperature

The more amount of simultaneous variables an instrument can measure, the higher it costs, especially when it operates at microwave frequencies. Moreover, the maintenance and calibration of specific and complex instruments seizes the budget and operation versatility of a laboratory. When a laboratory keeping the strategy of having independent variable-specific instruments requires a multi-variable characterization of a material, it might be possible using an intrinsic variable shared by all those measurements: the time. In this contribution, it is presented a way to combine independent computer-assisted data logging performed by a thermometer with the measurements logged from a dielectrometer. The internal clock of a personal computer is used as a reference for the data synchronization. It is also presented a practical example of this technique used for the characterization of the dielectric properties of mixtures of grape pomace with ethanol and water at 2.45 GHz in the range of 20 to 70ºC. The thermometer used was an OpSens TempSens along with optical-fiber sensors, which offers minimal perturbation of electromagnetic fields at 2.45 GHz. Its performance was calibrated using deionized water close to 0ºC. The continuous data logging which allowed monitoring the heating and cooling evolution of the samples was implemented under the Matlab platform through a RS-232 legacy port. The dielectrometer used was the Dielectric Kit for Vials, an instrument based on the cavity-resonator technology and manufactured by the ITACA research institute. Its performance was calibrated using deionized water at 20ºC. The data logging was performed manually using the instrument software provided by the manufacturer. The postprocessing of all the data collected from all instruments was implemented under the Matlab platform

Tutoría grupal para la resolución de problemas de síntesis de amplificadores sintonizados y análisis de mezcladores en ingeniería de telecomunicación

[SPA]En esta comunicación se explica la metodología de trabajo seguida en la ETSI de Telecomunicación de la Universidad Politécnica de Cartagena para el desarrollo de competencias de trabajo en grupo a través de la realización de tutorías grupales. Los alumnos elegidos para llevar a cabo estas actividades son los matriculados en la asiguatura optativa de Subsistemas de Radiofrecuencia, perteneciente a cuarto curso de la titulación de Ingeniero de Telecomunicación. La tuturía grupal se ha centrado en la resolución de problemas tipo de diseño de amplificadores sintonizados de radiofrecuencia así como el análisis de mezcladores. La propia evaluación del proceso por parte de los alumnos y los profesores muestran que los alumnos se sienten satisfechos en este tipo de actividades debido a la agilidad en la identificación de dudas y su resolución. Sin embargo, en los casos de alumnos sobresalientes el proceso puede ser un poco frustrante debido a su alto dominio previo de la asignatura. [ENG]In this communication, the methodology followed by teachers and students of the ETSI de Telecomunicación within Universidad Politécnica de Cartagena for the development of group cooperation competencies by means of group tutorials is explained. The chosen students for carrying out this activities belong to Radiofrequency Subsystems subject within the fourth academic year of Telecommunication Engineer Degree. Group Tutorial sessions have focused on 1474 typical RF tuned amplifiers design and mixer analysis problems. Students and teachers evaluation of the process shows that students are satisfied withi this kind of activities since doubts were quickly identified and solved. However, for outstanding students the process can be a bit frustrating due to their higher previous command of the subject.Campus Mare Nostrum, Universidad Politécnica de Cartagena, Universidad de Murcia, Región de Murci

A new sensor-based self-configurable bandstop filter for reducing the energy leakage in industrial microwave ovens

In this work a new sensor-based self-configurable waveguide bandstop filter that uses a combination of metallic irises and reconfigurable posts for reducing the energy leakage in industrial microwave ovens is presented and validated through a procedure fully based on measurements. Several optimization and reconfiguration alternatives of the moving posts such as genetic algorithms and parametric sweeps are assessed. Results show that good attenuation values can be obtained for all the analyzed scenarios. In particular, genetic algorithms are shown as the best search strategy. Design and optimization times are also reduced when using the proposed filter compared to computer simulations

Electromagnetic equivalent models for printed circuit boards inside a metallic enclosure Using a coaxial-to-waveguide transition calibration

Equivalent models of printed circuit boards are useful to simplify electromagnetic problems by reducing the computational costs of numerical simulations. In this paper, a new procedure for obtaining a simple equivalent model of printed circuit boards inside metallic enclosures is presented. The equivalent model is obtained in two steps: first we precisely characterize the coaxial to waveguide transitions used during measurements by means of an inverse procedure and then during a second inverse procedure, we carry out simulations by concatenating these transitions and the equivalent model and comparing to measurements. The optimized parameters for the equivalent model are: thickness, dielectric constant and the electric conductivity. Results for a printed circuit board in three scenarios have been obtained by using a sweep and two different optimization techniques. Benefits and drawbacks of the model are discussed. Results indicate that this procedure produces very precise characterization of the equivalent model of PCBs depending on the position and orientation of this device within the enclosure.This work was supported in part by the Fundación Séneca, Agencia de Ciencia y Tecnología de la Región de Murcia, under the Séneca predoctoral fellowship with reference 16381/FPI/10 and under the project 00700/PPC/0

Evaluation of graphite and TiO2 as susceptors for microwave dewaxing in ceramic shell casting processes of artworks

The main problems of the traditional foundry dewaxing processes in fine arts workshops are the emission of gases, the loss of 80% of the wax, the high electrical consumption, and the high risks for the operators. The introduction of the microwave technology for dewaxing of ceramic shell molds allows to minimize some of these problems, although the use of electromagnetic susceptors that capture the radiated energy and transform it into heat is required. This article describes different microwave dewaxing tests using TiO2 and graphite as susceptors. The results obtained show that this technique is viable, allowing the casting process to be carried out with a low percentage of breakage problems in the mold and significantly reducing the emitted gases and electricity consumption. The technique allows to recover in the same operation around 90% of the wax used in small and medium format objects. The tests show that the selection of the material used as a susceptor, the area of application and the power regimes, are fundamental to enable a controlled, soft and non-aggressive dewaxing, both for the art molds and for the environment, as opposed to the traditional Flash Dewaxing technique. In this way, it is possible to change the foundry of ceramic shells for artworks to achieve high levels of performance and safety, and to save energy, time and materials.This work is funded by the State Program for the Promotion of Scientific and Technical Research of Excellence around two projects in this line "Alternatives to dewaxing in the smelting of ceramic husks (ceramic shell casting): microwave technique", HAR2010-17570 (01/01/2011 - 30/04/2014) and "Alternatives to dewaxing in ceramic husks (ceramic shell casting): Microwave technique (II)", reference. HAR2016-77203-P (30/12/2016 - 29/12/2019)

Microondas: líneas de transmisión, guías de onda y cavidades resonantes

Como su título indica, este libro pretende servir de apoyo al estudio de la parte de la asignatura de Microondas relacionada con la teoría de líneas de transmisión y guías de onda, así como de otros dispositivos creados a partir de éstas, como las cavidades resonantes. Aunque existen en el mercado excelentes publicaciones sobre esta materia, con esta obra se ha intentado ajustar los contenidos con el fin de que éstos puedan ser impartidos de un modo claro y sosegado en un total de ocho semanas con tres horas semanales de clase magistral y de resolución de problemas. Se pretende seguir una estructura clara y progresiva que facilite el aprendizaje por parte del alumno o lector, incorporando contenidos teóricos y prácticos para cada uno de los temas planteados. Se han incluido en el texto de un modo detallado todas las demostraciones de importantes expresiones matemáticas con el fin de que el propio alumno sea capaz de seguirlas sin necesidad de que el profesor las desarrolle en clase. A lo largo de cada capítulo se desarrollan ejemplos y se plantean ejercicios a realizar por el lector. Asimismo, al final de cada capítulo se han añadido cuestiones de repaso y problemas. El capítulo de introducción define el concepto de microondas, repasa los principales hitos históricos en esta rama de la ingeniería y presenta un breve resumen de las aplicaciones fundamentales de las microondas. El estudio de líneas de transmisión se desarrolla a lo largo de los capítulos 2, 3 y 4. En el segundo se presenta la línea de transmisión ideal, estudiando su comportamiento tanto en el dominio del tiempo (análisis de transitorios) como en el dominio de la frecuencia, donde el análisis se centra en el uso del diagrama de Smith para adaptación de cargas. En el tercer capítulo se aborda el estudio de líneas de transmisión reales, presentando los conceptos de atenuación y dispersión y analizando las principales líneas con dos conductores. Para finalizar el estudio de líneas de transmisión, el capítulo 4 aborda el análisis de guías de onda, así como de modos superiores del cable coaxial, cuya resolución electromagnética presenta una dificultad superior. Aquí se presentan los modos transversal eléctrico y transversal magnético y se analizan sus características de propagación y de potencia. Este capítulo finaliza con el análisis de cavidades resonantes rectangulares y cilíndricas a partir del estudio previamente realizado sobre guías de onda

Improved control on the microwave devulcanizing of ground tire rubber by means of sulphur gas sensors

The success of a Ground Tire Rubber (GTR) devulcanization process relies on the elimination of the Sulphur atoms that are crosslinking the rubber polymer. From the Chemical point of view, this requires providing enough energy to break the Sulphur bonds while preserving the Carbon bonds, to ensure a high quality devulcanized GTR for being of interest to the rubber manufacturing industry. GTR is very responsive to microwaves due to the presence of Carbon Black (CB) in its composition, so the radiant energy is absorbed quickly in the form of thermal energy. When its temperature reaches 140°C, the breakage of Sulphur bonds may happen under an exothermic reaction, but also some new links might be built under that condition. Therefore, from the Physical point of view, the released Sulphur in the gaseous form of SO2, H2S, and/or CS2 must be promoted to abandon the reactor to avoid its recombination. In this work, microwave devulcanization is monitored by detecting the concentration of Sulphurous gases at the exhaust of the reactor. These sensors are very effective especially when pyrometer readings are degraded because of the gaseous layer on the GTR during the process.This research project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement number 870000. More information at https://valuerubber.eu/. The authors acknowledge CETEC and Synthelast for the GTR powder. Authors would like to extend the gratitude to Mr. Juan Antonio Albaladejo-López for his help with the mechanical development of the set u