Abstract
Neopentylglycol (NPG) and tris(hydroxymethyl)aminomethane (TRIS) are promising phase change materials (PCMs) for thermal energy storage (TES) applications. These molecules undergo reversible solid-solid phase transitions that are characterized by high enthalpy changes. This work investigates the NPG-TRIS binary system as a way to extend the use of both compounds in TES, looking for mixtures that cover transition temperatures different from those of pure compounds. The phase diagram of NPG-TRIS system has been established by thermal analysis. It reveals the existence of two eutectoids and one peritectic invariants, whose main properties as PCMs (transition temperature, enthalpy of phase transition, specific heat and density) have been determined. Of all transitions, only the eutectoid at 392 K shows sufficiently high enthalpy of solid-solid phase transition (150–227 J/g) and transition temperature significantly different from that of the solid-state transitions of pure compounds (NPG: 313 K; TRIS: 407 K). Special attention has also been paid to the analysis of metastability issues that could limit the usability of NPG, TRIS and their mixtures as PCMs. It is proven that the addition of small amounts of expanded graphite microparticles contributes to reduce the subcooling phenomena that characterizes NPG and TRIS and solve the reversibility problems observed in NPG/TRIS mixtures.
Highlights
Thermal energy storage (TES) is a key element in the energy transformation that our society must undergo in order to alleviate the effects of climate change and the scarcity of fossil resources.Traditionally, thermal energy storage (TES) has been used to improve thermal management and energy efficiency in the sector of heating and cooling in buildings, as well as in industrial heat processes
The samples of NPG and TRIS are submitted to three consecutive heating and cooling cycles at a heating/cooling rate of 5 K/min to check the repeatability of the results (Figure 1a)
NPG-TRIS binary system has been investigated in this study looking for mixtures that cover transition temperatures different from those of pure compounds, extending their potential use in TES applications
Summary
Thermal energy storage (TES) is a key element in the energy transformation that our society must undergo in order to alleviate the effects of climate change and the scarcity of fossil resources. TES has been used to improve thermal management and energy efficiency in the sector of heating and cooling in buildings, as well as in industrial heat processes. Thermal energy storage might become an essential tool for increasing the use of renewable energies, characterized by their temporal variability. It has experimented a important development coupled to low-medium temperature solar thermal collectors, as well as in concentrating solar thermal power plants.
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