Study on thermophysical properties of C₇∼C₉ binary alkane PCM and preparation of anti-volatile emulsion template for cryogenic thermal energy storage

In view of the present scarcity in the study of very low temperature (<−100 °C) phase change materials (PCMs) and the typical high volatility issue of these low temperature PCMs, the present work aims to develop the potential PCMs and select an appropriate anti-volatile method for cryogenic applications. In this work, cryogenic C₇∼C₉ n-alkanes were selected to prepare C₇-C₈ and C₇-C₉ binary systems, and their phase equilibrium behavior and thermophysical properties were investigated. For volatility problem, anti-volatility emulsion templates were successfully synthesized by high-energy emulsification method. The volatilization rate of the emulsion templates was characterized by combining DSC and mass transfer model, and the preparation parameters of the emulsion template with the finest anti-volatility were obtained. The results show that the eutectic compositions of C₇-C₈ and C₇-C₉ binary systems are 12 wt%C₈ and 10 wt%C₉, respectively. Both eutectic systems have eutectic temperatures suitable (−99.4 °C for C₇-C₈, −103.1 °C for C₇-C₉), satisfactory melting enthalpy (127.6 J/g for C₇-C₈, 129.7J/g for C₇-C₉), and good phase transformation reversibility for cryogenic energy storage. Under the optimized preparation parameters (WOR=2:1, EOR=18%, HLB=11.44), the volatilization coefficient of emulsion template is reduced from the maximum of 0.01408/min to 0.00236/min, which implies that the anti-volatility of emulsion is enhanced by nearly 6 times.