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Thermodynamic Calculations of Ternary Polyalcohol and Amine Phase Diagrams for Thermal Energy Storage Materials
Chemical and Materials Engineering
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Organic polyalcohol and amine globular molecular crystal materials as phase change materials (PCMs) such as Pentaglycerine (PG-(CH3)C(CH2OH)3), Tris(hydroxymethyl)aminomethane (TRIS-(NH2)C(CH2OH)3), 2-amino-2methyl-1,3- propanediol (AMPL-(NH2)(CH3)C(CH2OH)2), and neopentylglycol (NPG- (CH3)2C(CH2OH)2) can be considered to be potential candidates for thermal energy storage (TES) applications such as waste heat recovery, solar energy utilization, energy saving in buildings, and electronic device management during heating or cooling process in which the latent heat and sensible heat can be reversibly stored or released through solid state phase transitions over a range of temperatures. In order to understand the polymorphism of phase transition of these organic materials and provide more choice of materials design for TES, binary systems have been studied to lower the temperature of solid-state phase transition for the specific application. To our best knowledge, the study of ternary systems in these organic materials is limited. Based on this motivation, four ternary systems of PG-TRIS-AMPL, PG-TRIS-NPG, PG-AMPL-NPG, and TRIS- AMPL-NPG are proposed in this dissertation. Firstly, thermodynamic assessment with CALPHAD method is used to construct the Gibbs energy functions into thermodynamic database for these four materials based on available experimental results from X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The phase stability and thermodynamic characteristics of these four materials calculated from present thermodynamic database with CALPHAD method can match well the present experimental results from XRD and DSC. Secondly, related six binary phase diagrams of PG-TRIS, PG-AMPL, PG-NPG, TRIS-AMPL, TRIS-NPG, and AMPL-NPG are optimized with CALPHAD method in Thermo-Calc software based on available experimental results, in which the substitutional model is used and excess Gibbs energy is expressed with Redlich-Kister formalism. The thermodynamic database incorporating the optimized binary interactive parameters can produce the six binary phase diagrams matching the available experimental results very well and results in the correct interpretation of various phase transitions in these six binary phase diagrams. Finally, the related four ternary systems of PG-TRIS-AMPL, PG-TRIS-NPG, PG-AMPL-NPG, and TRIS-AMPL-NPG are proposed based on present thermodynamic database by means of CALPHAD method. Also, thermal characteristics, isothermal sections at several temperatures, isopleth section with various constant composition, and liquidus projections are calculated and presented in this dissertation.