Browsing by Author "Nikitin, Timur"
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- Enhancing low-temperature thermal energy storage with next-generation PCMsPublication . Sequeira, Maria Carolina; Nogueira, Bernardo; Nikitin, Timur; Diogo, Herminio; Caetano, Fernando J. P.; Fareleira, João; Fausto, RuiThe communication reports the potential use of PCM, n-alkanes and n-alkyl adipates, at low temperatures (between -80 ºC and -20 ºC) for different applications in the cold chain logistics such as the transport of medicines. For the phase equilibrium studies, of the different mixtures, techniques as differential Scanning Calorimetry (DSC), Hot-stage Polarized Microscopy and Raman Spectroscopy were used.
- 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.
- Phase equilibrium of n-Nonane + n-Decane for low-temperature thermal energy storage: insights into odd–even effectsPublication . Sequeira, Maria Carolina; Nikitin, Timur; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João; Fausto, RuiThe present article presents the solid–liquid phase diagram of a binary system composed of an n-alkane with an odd number of carbon atoms, namely, n-nonane (n-C9), with an even-numbered one, namely n-decane (n-C10). This work is part of a series of phase equilibrium studies on n-alkanes for low-temperature thermal energy storage (TES) applications. The ultimate purpose of this work is to investigate the adequacy of this binary system to be used as a Phase Change Material (PCM) at low temperatures. Additionally, along the equilibrium studies on linear alkanes, an interesting feature has emerged: the solid–liquid phase diagrams of binary n-alkane systems apparently show a striking dependence on the odd or even number of carbon atoms in their chains. The phase diagram for the system n-C9 + n-C10 has primarily been obtained using Differential Scanning Calorimetry (DSC), whose results have been complemented by Hot-Stage Microscopy (HSM) and low-temperature Raman Spectroscopy results. The DSC analysis provided both the temperature and enthalpy values for the observed solid–liquid and solid–solid phase transitions. The n-C9 + n-C10 binary system seems to display a peritectic solid–liquid phase diagram at low temperatures. The peritectic temperature found was 222.41 K, with a peritectic composition around xnonane = 0.60. Those results confirmed the initial suggestions that this would be a peritectic system, based on previously observed odd–even effects on phase equilibrium behavior of alkane mixtures. The goal of this work is to extend new insights into the solid–liquid phase equilibrium behavior of the binary system n-C9 + n-C10, a topic not yet covered in the literature. This information, consequently, provides practical and essential information on the potential use of this system as PCM for low-temperature TES applications. Additionally, it contributes to support the important discussion on the effect of odd–even number of carbons of the individual n-alkanes in the solid–liquid phase equilibrium behavior of their binary mixtures. The solid–liquid diagram of this system is being published for the first time, as far as the authors are aware.
- 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.; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Fausto , Rui; Diogo, Herminio; Nikitin, TimurOver 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 diagram of the dimethyl + dipropyl adipates system: application to low-temperature thermal energy storagePublication . Sequeira, Maria Carolina; Nikitin, Timur; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João; Fausto, RuiThe present study is the continuation of our research work on di-n-alkyl adipates and their potential as phase change materials (PCM) for low-temperature thermal energy storage (TES). The solid–liquid phase diagram for the binary system composed of dimethyl adipate (DMA) and dipropyl adipate (DPA) is presented and analysed. In a previous study, we explored a particular binary system of n-alkyl adipates, namely diethyl and dibutyl adipates, and demonstrated that these compounds possess underappreciated potential as PCMs at sub-zero temperatures. The goal of the current work is to expand on this research by contributing new phase equilibrium data and deepening our understanding of the fundamental thermodynamics governing low-temperature phase behaviour in di-n-alkyl-adipates. The phase diagram for the DMA + DPA binary system was obtained using three complementary techniques: differential scanning calorimetry (DSC), hot-stage microscopy (HSM), and Raman spectroscopy. DSC analysis of sixteen compositions, including the two pure compounds, provided both the temperature and enthalpy values for the solid–liquid and solid–solid phase transitions. The binary system displays eutectic behaviour at low temperatures, with the eutectic point found at 252.83 K and a composition of approximately xDPA = 0.77. Raman spectroscopy confirmed that the system is characterized by a non-isomorphic eutectic phase diagram, indicating differences in the crystal structures of the solid phases. The liquidus line of the binary phase diagram was successfully described using a suitable fitting equation, yielding a root mean square deviation of 0.65 K, indicating excellent agreement between the experimental data and the theoretical model. This fitting also allowed an accurate prediction of the eutectic composition and temperature. A Tammann diagram is also presented, further confirming the eutectic composition and associated enthalpy. This work addresses a gap in the literature by presenting, for the first time, the solid–liquid phase equilibrium behaviour of the DMA + DPA binary system (including the detailed solid–liquid phase diagram of the system). The findings provide valuable insight into the potential use of this system as PCM for sub-zero TES applications, supporting their consideration in future thermal energy storage technologies.
- 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.
- A thermodynamic journey: unlocking cold thermal energy storage with phase equilibrium studiesPublication . Sequeira, Maria Carolina; Nikitin, Timur; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João; Fausto, RuiAs the urgent demand for sustainable energy solutions increase, thermal energy storage (TES) systems have become crucial in improving energy efficiency and ensuring supply-demand balance. For low-temperature areas such as refrigeration, cold-chain logistics, and specific medical applications, phase change materials (PCM) are particularly valuable due to their high latent heat capacity and reversible phase transitions. However, finding PCM that are not only efficient and reliable, but also environmentally safe, remains a challenge. In this work we present the work done with several adipates and alkanes towards their use as PCM for low-temperature thermal energy storage.
- 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.
- Tuning thermal performance: the role of molecular asymmetry in di-n-alkyl adipates for efficient low-temperature thermal energy storagePublication . Sequeira, Maria Carolina; Nikitin, Timur; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João; Fausto, RuiThe development of efficient and sustainable thermal energy storage (TES) systems is crucial for improving energy efficiency in various applications, especially at low temperatures, such as cryogenic cooling, cold storage, logistics and transportation. Phase change materials (PCM) play a key role in TES, as they allow the storage and release of significant amounts of latent heat during phase transitions. In this context, our research group has been working on new materials, particularly binary systems, with potential application as PCM for efficient low-temperature TES1. As a result, di-n-alkyl adipates have recently emerged as promising candidates due to their favorable thermal properties, chemical stability, and phase change behavior2. Our previous work2 focused on the binary system of diethyl and dibutyl adipates, highlighted the potential of adipates as low-temperature PCM, motivating further research into their solid-liquid phase change behavior and structure-property relationships. Building upon this initial study, we have expanded our research into a broader range of di-n-alkyl adipates. One of the key aspects of our current research is the identification of eutectic compositions within adipate-based binary systems. Eutectic mixtures are particularly attractive as PCM enabling tunable phase transition temperatures to match specific TES requirements. Through the careful combination of results obtained from Differential Scanning Calorimetry (DSC), Hot-Stage Microscopy (HSM), and Raman Spectroscopy, a detailed phase diagram was methodically crafted to highlight the intricate eutectic behavior of these systems, identifying compositions that optimize thermal performance. In this study, the interplay between alkyl chain length and thermal behavior, particularly the influence of odd–even effects in binary systems is also approached. By selecting mixtures that combine odd-odd, even-odd or even-even substituent arrangements, we have explored how molecular asymmetry impacts solid-liquid phase change behavior. Our results reveal distinct trends, demonstrating how subtle structural variations can be leveraged to fine-tune the thermophysical properties of these materials. Our findings contribute to the growing field of organic PCM, demonstrating that di-n-alkyl adipates are viable candidates for low-temperature TES applications. By elucidating their phase change behavior, we provide a foundation for the innovative development of next-generation thermal storage materials, paving the way for more advanced and efficient solutions.