Robust optimization of heat-transfer-enhancing microtextured surfaces based on machine learning surrogate models

Currently, there is a growing industry-wide focus on enhancing the thermohydraulic performances of devices, with the goal of achieving more efficient energy management. However, due to manufacturing constraints, there has been a tendency to focus on simple geometric designs. Recently, the emergence of additive manufacturing techniques and advancements in artificial intelligence have enabled new possibilities in this field. In this work, a pioneering exploration of a novel methodology for optimization of microfins to enhance the heat transfer on flat surfaces is presented. The optimization is performed using data-driven algorithms to accelerate the evaluation of the performance of these surfaces; these algorithms are trained on a database of 15,694 numerical simulations of enhanced surfaces. The performance evaluation criterion (PEC), equal to the ratio between the thermal and hydraulic performance parameters of the geometry, is used as the objective function. To avoid an optimization that focuses solely on the compactness of the fins while ignoring their shape, the optimal geometry is sought, which proves to be a challenge. Hence, an optimization method that classifies the surfaces based on their periodicity is proposed, focusing on improving the performance in terms of the morphology. Results present a PEC augmentation range from +0.08 to +0.28.Universidade de VigoUniversidade de Vigo/CISU

Selection of non-financial sustainability indicators as key elements for multi-criteria analysis of hotel chains

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGNowadays, online information provided by corporate websites has a great impact on the hotel industry performance. According to existing studies, it is very likely that customers' and investors' decisions may change after consulting these portals. The environmental commitment of hotel companies is usually demonstrated to stakeholders by obtaining environmental quality certifications and eco-labels issued by specialised entities in compliance with certain requirements. However, the question of how to use the sustainable indicators that are usually scattered on the web or in company reports is a problemthat requires further research. The main objective of this study is to develop a robust and reliable model to assess the sustainability of hotel chains based on the information gathered from their websites and corporate reports. A literature review is carried out and specialists are consulted to determine the critical factors that affect hotel sustainability. Once the criteria based on nonfinancial indicators have been chosen, they are organised in a hierarchy according to their orientation. To achieve the objective of the study, a hybrid model is proposed that includes two multi-criteria decision-making approaches, namely the Analytic Hierarchy Process (AHP) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS)method. AHP is used to weight the criteria, and the ranking of the alternatives is provided through TOPSIS. Subsequently, a sensitivity analysis is performed to determine the critical indicators. Finally, a numerical example is carried out with a case study of the largest Spanish hotel chains to illustrate the function and applicability of the proposed method. With the results obtained, it has been possible to establish a ranking or selection of hotel chains for the case study, since the hybrid AHP-TOPSIS method provides reliable and robust results for any qualitative or quantitative evaluation criterion, which is of great interest for the different actors involved.Xunta de Galicia | Ref. GRC-202

Geostrategic study of the evolution of energy harvesting systems based on the patent activity of flywheels and regenerative shock absorbers

This paper analyses the technological activity on energy harvesting and storage systems, such as flywheels and regenerative shock absorbers, for support of renewable energy and electric vehicle applications. The activity is analyzed based on the evolution of the patents over the last 20 years, based on databases such as Patbase and Derwnet. The data reveal that less than 50 % of the total flywheels patents and utility models are granted. China is identified as the leading innovator in this area, followed by the United States, Japan, and Germany, which collectively account for 84 % of all patent families. A ranking of related companies and institutes is dominated by Chinese companies such as CANDELA (SHENZHEN) TECHNOLOGY INNOVATION CO., SHENYANG WEIKONG NEW ENERGY TECH CO., followed by German and American companies such as LUK LAMELLEN, VYCON, Siemens, and Caterpillar Inc. The leading regions on regenerative shock absorbers technologies are Germany, China, USA, and the European Patent Office (EPO). The study shows a leadership of Germany accounting for 39 % of the priority patents. The study also identified the top 20 applicants with the highest number of patent families, which included European companies such as SCHAEFFLER AG, HYDAC, VOLKSWAGEN AG, and Continental Automotive GmbHUniversidade de Vigo/CISUGAgencia Estatal de Investigación | Ref. PID2021-126569OB-I0

On the Physical Vapour Deposition (PVD): evolution of magnetron sputtering processes for industrial applications

Advanced coatings play an important role in a wide range of industrial applications. These coatings are commonly used in machining tools due to their high hardness and wear resistance, but also can be applied in jewellery and decorative purposes. Deposition techniques have seen a strong evolution as result of the directly related devices, control evolution and software. Several variants have been developed around the main techniques: arc evaporation and sputtering. The coatings produced present significant differences in their characteristics, namely in terms of structure, mechanical properties and surface morphology. Depending on the substrate material and application, the deposition process needs to be properly selected, providing the particular characteristics requested. This paper intends to do a critical review of the evolution of the advanced coatings deposition process, mainly focused on the Physical Vapour Deposition (PVD) process, particularly in the Magnetron Sputtering technique, which is able to produce smooth surfaces, using lower temperatures, presenting excellent mechanical and tribological properties and having very good adhesion to the main materials used as substrate.Fundação para a Ciência e a Tecnologia | Ref. UID/EMS/0615/2016LAETA/CETRIB/INEGI Research Center-FLAD – Fundação Luso-Americana para o Desenvolvimento | Ref. 116/201

Development of a transient model of a Stirling-based CHP system

Although the Stirling engine was invented in 1816, this heat engine still continues to be investigated due to the variety of energy sources that can be used to power it (e.g., solar energy, fossil fuels, biomass, and geothermal energy). To study the performance of these machines, it is necessary to develop and simulate models under different operating conditions. In this paper, we present a one-dimensional dynamic model based on components from Trnsys: principally, a lumped mass and a heat exchanger. The resulting model is calibrated using GenOpt. Furthermore, the obtained model can be used to simulate the machine both under steady-state operation and during a transient response. The results provided by the simulations are compared with data measured in a Stirling engine that has been subjected to different operating conditions. This comparison shows good agreement, indicating that the model is an appropriate method for transient thermal simulations. This new proposed model requires few configuration parameters and is therefore easily adaptable to a wide range of commercial models of Stirling engines. A detailed analysis of the system results reveals that the power is directly related to the difference of temperatures between the hot and cold sources during the transient and steady-state processes

A critical review on the numerical simulation related to Physical Vapour Deposition

Physical Vapour Deposition (PVD) is a process usually used for the production of advanced coatings regarding its application in several industrial and current products, such as optical lens, moulds and dies, decorative parts or tools. This process has several variants due to its strong evolution along the last decades. The process is commonly assisted by plasma, creating a particular low pressure and medium temperature atmosphere, which is responsible for the transition of atomic particles between the target and the parts to be coated into a vacuum reactor. Several parameters are directly affecting the deposition, namely the substrate temperature, pressure inside the reactor, assisting gases used, type of current, power supply, bias, substrate and target materials, samples holder and corresponding rotation, deposition time, among others. Many mathematical models have been developed in order to allow the generation of numerical simulation applications, trying to combine parameters and expect the corresponding results. Numerical simulation applications were created around the mathematical models previously developed, which can play an important role in the prediction of the coating properties and structure. This paper intends to describe the numerical simulation evolution in the last years, namely the use of Finite Elements Method (FEM) and Computational Fluid Dynamics (CFD).LAETA/CETRIB/INEGI Research Center- FLAD – Fundação Luso-Americana para o Desenvolvimento | Ref. 116/2018Fundação para a Ciência e a Tecnologia | Ref. UID/EMS/0615/201

Contribución al estudio de la combustión de biomasa en lecho fijo: análisis de la fase limitada por oxígeno

Diversos trabajos se llevan a cabo en la actualidad en quemadores experimentales de biomasa de lecho fijo. Su geometría simplificada, la obtención precisa de datos intra-lecho y su elevada operatividad han contribuido al desarrollo de estos sistemas [1-3]. A pesar de la gran cantidad de estudios desarrollados, todavía existe cierta discrepancia o falta de información acerca de la estructura interna del lecho. Con esto en mente, el presente trabajo pretende establecer algunas ideas generales a cerca del proceso de combustión en el lecho o zona de entrada de aire primario (gasificación), enfocada en la fase de combustión heterogénea de char bajo condiciones limitadas por la ausencia de oxígeno. Para ello, se analizan datos experimentales de un quemador de alimentación inferior con aire zonificado en términos de régimen de combustión y relación estequiométrica. Los resultados muestran una clara relación entre la tasa de combustión y el reparto de aire 1º/2º. Además, cuanto mayor es el suministro de aire, mayor es el consumo de combustible. En esencia, el incremento de material gasificado (volatilizado) en la zona de combustión primaria reacciona adecuadamente con el aire secundario, liberando mayor calor y evitando que se alcance la situación de enfriamiento por convección. Como consecuencia, el rango de aire de trabajo útil obtenido es muy amplio, pero el exceso con el que se produce (λ) se mantienen aproximadamente constante. Dicho de otro modo, existe un incremento proporcional entre el caudal de aire suministrado y el combustible quemado. Profundizando en el análisis de la fase de combustión heterogénea, se encontró que la tasa de consumo es proporcional al suministro de aire primario, independientemente del reparto aplicado. Esto indica que la tasa de reacción depende exclusivamente de la tasa de suministro de oxígeno al lecho o frente de reacción. De hecho, el exceso de aire referido a la combustión completa de char para obtener CO2 (λC) se mantiene constante y cercano al estequiométrico. Los resultados mencionados parecen respaldar la idea de que la tasa de reacción de char (oxidación y reducción) en un quemador de alimentación inferior y con reparto de aire está limitada por la presencia de oxígeno en un amplio rango de trabajo. En estas condiciones, la tasa de reacción viene determinada totalmente por el suministro de aire primario, de manera casi independiente a otras variables operativas.Los autores agradecen el apoyo financiero del Ministerio de Economía y Competitividad a través del proyecto ENE2012-36405

Evaluación del mercado europeo de calderas de pellet de baja potencia

Este trabajo analiza las características tecnológicas del uso de pellets para el mercado de baja potencia dentro del mercado europeo. Se pretende valorar el estado del arte de calderas y su adaptación a los recientes cambios normativos derivados de la revisión de la norma EN-303-5-2012. Para ello se ha realizado un amplio estudio de mercado creando una base de datos que incluye más de 150 empresas y más de 600 tipos de calderas, lo que permite estudiar la situación actual del mercado en la mayoría de países de Europa. En este estudio se entiende como unidades de baja potencia, aquellas con una potencia inferior a los 200 kW. Las peculiaridades tecnologías de estas unidades son descritas y comparadas en términos de eficiencia y de emisiones de gases contaminantes, y también dentro del marco de la nueva normativa europea. El gran número de relativamente nuevas compañías muestra el creciente interés no solo del uso de pellets, sino del desarrollo de la tecnología para su uso en la producción de calor. No obstante este estudio muestra que este mercado sigue dominado por las empresas austriacas y alemanas, tanto en el número de empresas como por la variedad de productos ofertados. La tecnología imperante es la caldera pirotubular vertical, con un intercambiador posicionado por encima de un lecho de pellet fijo. El control de la caldera a través de una sonda lambda sigue siendo un característica mayoritaria solo del rango de potencias más altas (>24kW). También se constata que la revisión de la norma europea era necesaria, pues la versión de 1999 no permitía segmentar el mercado, ya que prácticamente la mayoría de las calderas conseguían anteriormente la máxima calificación, lo que en la práctica dejaba sin efecto la escala de calificación, y no permite al consumidor distinguir entre las calderas mejores y peores.CaLos autores agradecen el apoyo financiero del Ministerio de Economía y Competitividad a través del proyecto ENE2012-3640

Novel test bench for the active reduction of biomass particulate matter emissions

This paper introduces an experimental plant specifically designed to challenge the main operating issues related to modern biomass combustion systems (mainly NOx, particulate matter, and deposition phenomena). The prototype is an 11–18 kW overfed fixed-bed burner with a modular configuration, and the design considers the implementation of certain strategies for improving combustion: (1) a complete refrigeration system that also includes the fuel bed; and (2) an air injection control through flue gas recirculation. First, the stability and repeatability of the facility were successfully tested, establishing the duration of transient periods in the phase of experiment design. The results revealed similar effects in temperature and particulate emissions when comparing the use of the cooling bed and recirculation techniques. Reductions of 15% and up to 70% were achieved for the exhaust temperature and particulate matter concentration, respectively. Otherwise, the refrigeration considerably reduced the bed temperature, especially in its core, which enhanced the condensation of volatile salts and therefore the fouling phenomena. Although the viability of using both techniques as temperature control methods is demonstrated, further studies are needed to clarify the specific effects of each technology and to clarify the possible significance of a hybrid solution that combines both strategies.Ministerio de Ciencia, Innovación y Universidades | Ref. RTI-2018-100765-B100Ministerio de Educación, Cultura y Deportes | Ref. FPU-15/0243

Study on the influence of the ball material on abrasive particles’ dynamics in ball-cratering thin coatings wear tests

Micro-abrasion remains a test configuration hugely used, mainly for thin coatings. Several studies have been carried out investigating the parameters around this configuration. Recently, a new study was launched studying the behavior of different ball materials in abrasive particles’ dynamics in the contact area. This study intends to extend that study, investigating new ball materials never used so far in this test configuration. Thus, commercial balls of American Iron and Steel Institute (AISI) 52100 steel, Stainless Steel (SS) (AISI) 304 steel and Polytetrafluoroethylene (PTFE) were used under different test conditions and abrasive particles, using always the same coating for reference. Craters generated on the coated samples’ surface and tracks on the balls’ surface were carefully observed by Scanning Electron Microscopy (SEM) and 3D microscopy in order to understand the abrasive particles’ dynamics. As a softer material, more abrasive particles were entrapped on the PTFE ball’s surface, generating grooving wear on the samples. SS AISI 304 balls, being softer than the abrasive particles (diamond), also allowed particle entrapment, originating from grooving wear. AISI 52100 steel balls presented particle dynamics that are already known. Thus, this study extends the knowledge already existing, allowing to better select the ball material to be used in ball-cratering tests