Time-Controlling the Latent Heat Release of Fatty Acids using Static Electric Field

Abstract

Latent heat released during freezing of phase change material (PCM), which occurs at a constant temperature, can be modified using an electric field, through a process called electrofreezing. To date, the effects of the electric field on the freezing of salt solutions or salt hydrates of inorganic PCM, such as reduction of the supercooling degree, increase of nucleation rate, and reduction of the induction time due to changes in the Gibbs free energy, have been the focus. In this paper, we describe the electrofreezing of stearic acid and lauric acid of fatty acid PCM. Because common organic PCM has relatively small or even zero supercooling, the effect of the DC electric field on the time of latent heat release at a constant temperature and crystallization time was more pronounced. A comparison was also done with inorganic CaCl2⋅6H2O PCM using previously published data. We propose that the two time parameters are closely related to the electrical and thermal conductivities. Different nucleation mechanisms for fatty acids and CaCl2⋅6H2O with interactions between the crystalline sample and electric field, as well as dissimilar Joule heating effects, have been proposed. Changes in the chemical structure and thermal stability due to electric field treatment are evaluated using the Fourier-transform infrared spectra, the decomposition and melting temperatures, and the calculation of the latent heat of fusion. We also discuss the potential applications of lauric and stearic acids as phase change composites in thermoresponsive devices for high electrical to thermal energy conversion efficiencies.