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Browsing Ciências e Tecnologia / Sciences and Technology by Field of Science and Technology (FOS) "Engenharia e Tecnologia::Engenharia Química"
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- Capillary viscometry for routine measurements of newtonian liquidsPublication . Sequeira, Maria Carolina; Caetano, Fernando J. P.; Fareleira, João M. N. A.Viscosity is a thermophysical property of paramount importance, being essential for many scientific and industrial applications. The most common instruments for its measurement are glass capillary viscometers. Therefore, the use of capillary viscometers is widespread both in industry and in research. The range of viscosities of interest range from lower than that of water to several orders of magnitude higher values, the measurement of which requires different capillary viscometers. Most of the practical applications concern routine instruments, mainly for quality control. One main issue for the utilization of capillary viscometers relates to the need for their calibration, assuring its traceability to the water primary viscosity standard, to certify its worldwide validity. The present paper focuses on capillary instruments dedicated to perform viscosity measurements on Newtonian organic liquids at atmospheric pressure, as it is assumed that is the most widespread type of application for these viscometers. Capillary viscometry has a completely well-defined working equation, namely, the Hagen–Poiseuille equation. However, the practical performance of the measuring instruments deviates from that working equation. Most of those deviations are currently considered by many users. However, some of those deviations have not reached that status yet, like those concerning the effects due to the surface tension of the sample on the measurements. All these aspects are summarized and analyzed in the present article, together with a brief general description of the most common types of capillary viscometers, namely, the Ostwald and the constant-level or Ubbelohde instruments.
- Correction: Di-Alkyl Adipates as new phase change material for low temperature energy storagePublication . Nogueira, Bernardo A.; Diogo, Hermínio P.; Fausto, Rui; Caetano, Fernando J. P.; Fareleira, João; Sequeira, Maria CarolinaThe following is a correction to the supplementary information of the paper titled “Di-Alkyl Adipates as new phase change material for low temperature energy storage” by Maria C.M. Sequeira, Bernardo A. Nogueira, Fernando J.P. Caetano, Hermínio P. Diogo, João M.N.A. Fareleira, Rui Fausto that appeared in International Journal of Thermophysics 44:165 (2023). https://doi.org/10.1007/s10765-023-03274-3
- O equilíbrio químico é um processo dinâmicoPublication . Fernandes, Tiago
- IsomerismoPublication . Fernandes, Tiago
- 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.
- 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 of the n-Nonane + n-Undecane system for low-temperature thermal energy storagePublication . Nikitin, Timur; Sequeira, Maria Carolina; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Fausto , Rui; Diogo, HerminioThe current article presents an exploration of the solid–liquid phase diagram for a binary system comprising n-alkanes with an odd number of carbon atoms, specifically n-nonane (n-C9) and n-undecane (n-C11). This binary system exhibits promising characteristics for application as a phase change material (PCM) in low-temperature thermal energy storage (TES), due to the fusion temperatures of the individual components, thereby motivating an in-depth investigation of the solid–liquid phase diagram of their mixtures. The n-nonane (n-C9) + n-undecane (n-C11) solid–liquid phase equilibrium study herein reported includes the construction of the phase diagram using Differential Scanning Calorimetry (DSC) data, complemented with Hot–Stage Microscopy (HSM) and low-temperature Raman Spectroscopy results. From the DSC analysis, both the temperature and the enthalpy of solid–solid and solid–liquid transitions were obtained. The binary system n-C9 + n-C11 has evidenced a congruent melting solid solution at low temperatures. In particular, the blend with a molar composition xundecane = 0.10 shows to be a congruent melting solid solution with a melting point at 215.84 K and an enthalpy of fusion of 13.6 kJ·mol–1. For this reason, this system has confirmed the initial signs to be a candidate with good potential to be applied as a PCM in low-temperature TES applications. This work aims not only to contribute to gather information on the solid–liquid phase equilibrium on the system n-C9 + n-C11, which presently are not available in the literature, but especially to obtain essential and practical information on the possibility to use this system as PCM at low temperatures. The solid–liquid phase diagram of the system n-C9 + n-C11 is being published for the first time, as far as the authors are aware.
- Solid–liquid phase equilibrium: alkane systems for low-temperature energy storagePublication . Diogo, Hermínio P.; Fausto , Rui; Sequeira, Maria Carolina; Fernando J. P. Caetano; Fareleira, João M. N. A.; Nogueira, Bernardo A.The thermal characterization of two binary systems of n-alkanes that can be used as Phase Change Materials (PCMs) for thermal energy storage at low temperatures is reported in this work. The construction of the solid–liquid binary phase diagrams was achieved using differential scanning calorimetry (DSC) and Raman spectroscopy. The solidus and liquidus equilibrium temperatures were determined using DSC for thirty-nine different samples, three for the pure n-alkanes and the remaining for binary mixtures at selected molar compositions and used to acquire the corresponding solid–liquid phase diagrams. The two binary systems of n-octane/n-decane (C8/C10) and n-decane/n-dodecane (C10/C12) are characterized by a eutectic behavior at low temperatures. The eutectic temperature for the system C8/C10 was found at 211.95 K and the eutectic composition appeared at the molar fraction xoctane = 0.87. For the system C10/C12, the eutectic temperature was found at 237.85 K, and the eutectic composition appeared for the molar fraction xdecane = 0.78. This work aims to fulfill the lack of available data in the existing literature, considering the potential application of these systems for low-temperature thermal energy storage. Raman spectroscopy was used to complement the DSC data for the construction of the solid–liquid phase equilibrium diagrams, enabling the identification of the solid and liquid phases of the system. Additionally, the liquidus curve of the phase diagram was successfully described using a modified freezing point depression curve as fitting equation, the absolute root mean square deviation for the data correlation of the C8/C10 and C10/C12 systems being 2.56 K and 1.22 K, respectively. Ultimately, the fitting procedure also enabled a good prediction of the eutectic point for both studied systems.
- 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.