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Título : | Assessing the Long-Term Stability of Fatty Acids for Latent Heat |
Autor : | Bayón, Rocío Bonanos, Aristides Rojas, Esther |
Palabras clave : | PCM, lauric acid, TG measurements, kinetic analysis, multi-step processes |
Fecha de publicación : | 2020 |
Editorial : | International Solar Energy Society |
Citación : | doi:10.18086/eurosun.2020.07.10 Available at http://proceedings.ises.org |
Resumen : | The thermal degradation kinetics of lauric acid has been studied with the aim of assessing its long-term stability
and performance as a latent heat storage medium for low temperature applications. For this purpose, dynamic
thermogravimetric (TG) measurements were carried out under different gas atmospheres (N2 and air) and at
various heating rates. The kinetic analysis of TG curves assuming a zero-order evaporation process led to
activation energy values very close to the evaporation enthalpy although the simulated dα/dT curves could not
reproduce the ones experimentally obtained. On the other hand, the analysis of TG measurements with a modelfree
isoconversional method has shown that the activation energy significantly varies with the degree of
conversion. All these results indicate that thermal degradation of lauric acid is a multi-step process whose
single-step mechanisms have to be identified. A deconvolution analysis of dα/dT curves was performed by using
Fraser-Suzuki functions so that two single-step reaction mechanisms were proposed: the first associated with the
evaporation with an activation energy value of 83±8 kJ/mol, while the other may be related to the emission of
volatile compounds. The activation energy value of the second mechanism is lower when lauric acid is heated
up in air, which may indicate that O2 is involved in the reaction. The calculated TG curves, assuming the
occurrence of these two mechanisms, fit very well to the corresponding experimental curves. Isothermal
degradation curves have been calculated by considering both mechanisms and, according to them, lauric acid
should totally disappear after 30 days if it is kept under N2 at 5 ºC above its melting temperature. However
preliminary isothermal test in an oven with small samples (in the range of few grams) disagree with those
predictions. Hence further isothermal experiments under conditions closer to the real service ones are required
in order obtain reliable isothermal degradation curves and assess long-term stability of lauric acid. |
URI : | http://documenta.ciemat.es/handle/123456789/1377 |
Aparece en las colecciones: | Artículos de Energía
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