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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
- 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.