Ciências e Tecnologia | Comunicações em congressos, conferências, seminários/Communications in congresses, conferences, seminars
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Browsing Ciências e Tecnologia | Comunicações em congressos, conferências, seminários/Communications in congresses, conferences, seminars by Sustainable Development Goals (SDG) "07:Energias Renováveis e Acessíveis"
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- Adipates as new phase change material: seeking for a low temperature energy storage systemPublication . Sequeira, Maria Carolina; Nogueira, Bernardo A.; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João M. N. A.; Fausto, RuiThe recent and endless increasing need for energy is requiring imperative and efficient solutions. Renewable energies are an effective solution, but they are also intermittent, which often leads to a gap between the availability of energy and its demand. Therefore, energy storage becomes crucial for improving the efficiency by reducing the mismatch between demand and supply thus offering better management capabilities. The use of phase change materials (PCMs) became an attractive technology, especially for active cooling systems. In particular, eutectic systems can be designed for each application, allowing significant energy savings, which is very relevant in what concerns economic and environmental sustainability [1]. Equilibrium studies and their phase diagrams are crucial to characterize the behavior of these systems, particularly for new PCMs [2]. This work aims the characterization of a selected type of binary system composed by di-n-alkyl adipates that can be used for energy storage at low temperatures, starting by the construction of solid-liquid phase diagram based on Differential Scanning Calorimetry (DSC) and Raman Spectroscopy results. The studied system is a binary mixture of diethyl and dibutyl adipates and reveals to behave as a eutectic system at low temperatures, possessing also polymorphism, therefore presenting a relatively complex phase diagram. The eutectic point was found around -33ºC and the polymorphism transition, being characteristic of the dibutyl adipate, occurs at around -36ºC for the overall phase diagram. Raman spectroscopy was fundamental concerning the construction of the phase diagram, enabling to identify the different solid and liquid phases of the system. This work provides new phase equilibrium data, which, to the knowledge of the authors, are the first in the literature, concerning these compounds. The studied binary system has promising characteristics for low temperature energy storage. It is also demonstrated how solid-liquid-phase equilibrium studies are the key to select the most appropriate phase change material for a specific thermal energy storage (TES) application.
- Low temperature energy storage PCM systems: phase equilibrium studiesPublication . Sequeira, Maria Carolina; Nogueira, Bernardo A.; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João M. N. A.; Fausto, Rui
- Low temperature thermal energy storage: insights into odd-even n-alkane systemPublication . Sequeira, Maria Carolina; Nogueira, Bernardo; Nikitin, Timur; Caetano, Fernando J. P.; Diogo, Herminio; Fausto, Rui; Fareleira, João M. N. A.
- On capillary viscosity measurements: how far do surface tension effects go?Publication . Sequeira, Maria Carolina; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João M. N. A.; Santos, Fernando J. V.; Serro, A. P.Viscosity is a fundamental thermophysical property of liquids making it very important particularly in the industry. Capillary viscometers have been widely used for viscosity measurements in different applications, the most relevant being the definition of viscosity standards, traceable to the primary water viscosity standard, by metrological institutions and industrial applications, mostly for quality control. Practical viscometry is based on the internationally accepted primary standard value for the kinematic viscosity of water at 20ºC and atmospheric pressure, which has been measured using capillary viscometers [1]. However, due to the water surface tension, viscosity measurements which have been related to water as a primary standard, can be significantly affected. It is difficult to rigorously assess the surface tension effects on capillary viscometers, and the practical way to avoid this problem is to use long capillaries, which are not appropriate for routine measurements [1-3]. After several experimental studies, using different types of viscometers, the usual procedure to correct surface tension effects in capillary viscosity measurements adopted by different authors, is to employ an empirical expression [1-4]. Additionally, other types of problems exist as the need to perform a kinetic energy correction which must also be taken into consideration [1]. The main goal of this work was to perform the calibration of a suspended-level, or Ubbelohde, capillary viscometer, which is not a long capillary viscometer, as well as the study of corrections to be used for the measurements performed with it. The experimental work covers the calibration of that Ubbelohde capillary viscometer, the evaluation of the uncertainty of the corresponding viscometer constant and the overall uncertainty of the measurements performed with it. This study includes the evaluation of the necessary corrections for kinetic energy and surface tension effects and, finally, the analysis of the case of a set of measurements performed with n-tetradecane. The ultimate purpose of this work is to obtain the lowest uncertainty for the Ubbelohde capillary viscometer 541 01/Ia, and to understand the need for the corrections that must be considered when using capillary viscometers and how they should be applied.
- Revisiting odd-even effects in n-alkane systemsPublication . Fausto, Rui; Sequeira, Maria Carolina; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João M. N. A.; Nikitin, Timur; Fausto, Ruin-Alkanes have been widely studied for different applications. Recently, they became still more popular due to their exceptional characteristics as phase change materials (PCMs) for thermal energy storage (TES) applications [1]. In our research group, during the last three years, we have been studying the phase equilibrium behaviour of some binary systems with potential application as PCMs, including n-alkanes [2,3]. In this study, the n-alkanes family has shown some intriguing effects, related to the odd or even number of carbon atoms of the molecules on the characteristics of their solid-liquid phase equilibria. Several studies regarding the solid phase properties have been carried out to understand this type of phenomena in n-alkanes and compounds whose molecules contain alkyl groups. It has been established that n-alkanes exhibit different crystal packing arrangements according to their odd or even number of carbon atoms in their chains [4]. As a result, several properties are seen to be affected by the number of carbon atoms, revealing remarkable odd-even effects, which can eventually be used as an advantage for some specific applications [5]. This is particularly important to interpret and predict the solid-liquid phase equilibrium types of the diagrams, which is a key issue to select PCMs for TES applications. Most of the studies involving the properties of n-alkanes are devoted to the liquid phase. Therefore, along the years, a wide range of properties have been measured, predicted, correlated, and interpreted, including viscosity, density, heat capacity, vapour pressure, flash point, boiling point, and thermal conductivity. It is generally known that linear alkanes are an interesting homologous series, because they show a considerable regularity in their fluid phase properties, which allows to establish, for example, simple correlations based on the number of carbon atoms in the molecular chain [4]. Because of the raising importance of energy storage, namely TES, and the application of alkanes as PCMs, interest in their solid-liquid phase equilibria has increased. Consequently, it is interesting to picture an overall image on the thermophysical properties of n-alkanes, and, in particular to study the predictability of the main characteristics of their solid-liquid phase equilibria. Thus, this work aims to be a comprehensive view on the thermophysical properties and phase equilibrium behaviour of n-alkanes and their relation to the odd or even carbon atoms present in the alkyl chain.
- Seeking new low temperature energy storage systems: n-alkanes as phase change materialsPublication . Sequeira, Maria Carolina; Nogueira, Bernardo A.; Nikitin, Timur; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Fausto , Rui; Diogo, HerminioOver the last decades, the increasing need for energy has been a tremendous challenge. Until now, fossil fuels have been the dominant energy source, however, due to their environmental consequences, renewable energies are the promising solution for the future.1 Nevertheless, the intermittent nature of most renewable energy sources often leads to a discrepancy between the energy produced and its consumption, which highlights the crucial role of energy storage technologies in enhancing clean energy utilization.2 From all energy storage solutions, thermal energy storage (TES) is one of the most promising options, showing substantial energy storage capacity at an acceptable cost.3 For these applications, phase change materials (PCMs) are particularly important, especially for low temperature energy storage systems. Linear alkanes (n-alkanes) have been studied as good candidates for TES applications mainly due to their singular phase transition performance, among others.4 In the present work, it has also been studied the differences due to the odd-even carbon chain number on the solid-liquid equilibrium properties that these materials can present, which is a key aspect crucial to characterize the systems for an upcoming use as PCMs. 4,5 to be used as new PCMs For TES applications, solid-liquid phase equilibrium is determinant to characterize the phase transitions which are more important for the application of these systems, as new PCMs. As an example, in the logistics associated to the transport of perishable consumables, like vaccines and other pharmaceutical products, TES plays an important role. In the present context, this work aims at the characterization of some selected n-alkane binary systems that can be used for energy storage applications at low temperatures, including the construction of the solid-liquid binary phase diagrams at sub-zero temperatures using differential scanning calorimetry (DSC), hot stage microscopy (HSM) and Raman spectroscopy. The studied systems composed by odd and even n-alkanes, have showed different solid-liquid equilibrium behaviour. The HSM and Raman spectroscopy were fundamental to obtain the binary phase diagrams, but also to visualize the changes taking place in real time as a function of temperature and often the identification of the different solid and liquid phases exhibited by these systems. This work presents some preliminary phase equilibrium data, which, to the knowledge of the authors, are not available in the literature, and are presently being prepared for publication in an international scientific journal. The presentation will also include comparisons with spread literature data, when available. All these studied systems have promising characteristics for low temperature energy storage. With this work, it is also demonstrated how solid-liquid phase equilibrium studies are a central key to select the most adequate phase change material for a specific TES application.
- Solid-liquid phase equilibrium: alkane systems for low temperature energy storagePublication . Sequeira, Maria Carolina; Nogueira, Bernardo A.; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João M. N. A.; Fausto, RuiThe incessant and increasing need for energy requires urgent and effective solutions. The supply of renewable energies is mainly intermittent, which often leads to a gap between the availability of energy and its consumption. Therefore, energy storage becomes imperative for increasing the efficiency in the use of the produced energy. Concerning this, the use of phase change materials (PCMs) has taken a very important role, especially for active cooling systems. In particular, eutectic systems can be designed with characteristics that make them suitable for each application, allowing significant energy savings, which is very relevant in what concerns economic and environmental sustainability [1]. This work aims to the characterization of selected systems that can be used for energy storage at low temperatures, starting by the construction of solid-liquid phase diagrams using differential scanning calorimetry (DSC) and Raman Spectroscopy results. Phase diagrams are crucial to characterize the behaviour of these systems and reveals the robustness of the PCM, and for new PCMs, equilibrium studies are essential to achieve the desired melting temperature [2]. This work is focused on binary systems composed by normal alkanes, in particular, the binary mixtures C8-C10 and C10-C12. These systems revealed to behave as eutectic systems at low temperatures, showing a promising applicability for thermal energy storage for low temperature applications. The eutectic points are around -61ºC and -35ºC, respectively. Additionally, a fitting equation for the experimental liquidus lines of the phase equilibrium diagrams is proposed for each system.
- Thermophysical properties of n-alkane system for low temperature thermal energy storagePublication . Nogueira, Bernardo A.; Nikitin, Timur; Diogo, Hermínio P.; Fausto, Rui; Fareleira, João; Caetano, Fernando J. P.; Sequeira, Maria CarolinaOver the past few decades, the escalating need for energy has posed a significant and pressing challenge. For centuries, fossil fuels stood as the dominant energy source; however, due to their dwindling availability and environmental complications, renewable energies have emerged as the promising solution for the future [1]. The intermittent nature of renewable energy sources often results in a disconnect between energy production and consumption, underscoring the vital role of energy storage technologies in enhancing clean energy utilization [2]. Among various energy storage solutions, thermal energy storage (TES) shines as one of the most promising options, offering substantial energy storage capacity at a relatively low cost [3]. In this context, phase change materials (PCMs) are particularly crucial, namelyfor active cooling systems. N-alkanes have been widely investigated for TES applications due to their singular characteristics including their phase transition performance, among others [4]. The objective of this work is to characterize selected n-alkane systems, involving the construction of the solid-liquid binary phase diagrams, using differential scanning calorimetry (DSC) and Raman Spectroscopy. Additionally, the present research efforts seek to obtain the thermal conductivity of these systems. The ongoing investigations play a critical role towards understanding the properties of these systems, enabling to predict their thermal characteristics and performance as PCMs for TES applications. Particularly, for new PCMs phase equilibrium studies are essential to select the appropriate systems with the desired properties for each application. This work is focused on binary systems composed by odd and even alkanes, in particular the binary mixtures C8–C10, C9–C10, C9–C11 and C10–C12. These systems revealed different solid-liquid phase equilibrium behaviour at low temperatures, although three of these four systems exhibited promising capabilities to be used for TES applications at low temperatures. Detailed results on these binary systems will be presented and discussed.