Degradation of Fatty Acid Phase-Change Materials (PCM): New Approach for Its Characterization.

The use of adequate thermal energy storage (TES) systems is an efficient way to achieve thermal comfort in buildings reducing the cooling and heating demand. Besides, deploy phase change materials (PCM) to meet and enhance the TES needs is highly effective and widely studied. In this paper, a study of the degradation of two fatty acids is presented, capric and myristic acids, in order to evaluate whether their thermo-physical properties are affected throughout time during service. This was carried out by means of two different types of thermal treatments: degradation at constant temperature (thermal stability test), 60 °C during 100 h and 500 h, and degradation with heating and cooling cycling (thermal cycling stability), between a temperature range from 15 °C to 70 °C with 0.5 °C/min ramp during 500 and 1000 cycles. Despite no significant changes were measured for myristic acid, experimental results revealed a decrease of melting enthalpy of 6.6% in capric acid thermally treated for 500 h. Evidences of chemical degradation were found that might explain the decrease in thermophysical properties during use.

Own-Synthetize Nanoparticles to Develop Nano-Enhanced Phase Change Materials (NEPCM) to Improve the Energy Efficiency in Buildings.

The use of adequate thermal energy storage (TES) systems is an opportunity to increase energy efficiency in the building sector, and so decrease both commercial and residential energy consumptions. Nano-enhanced phase change materials (NEPCM) have attracted attention to address one of the crucial barriers (i.e. low thermal conductivity) to the adoption of phase change materials (PCM) in this sector. In the present study two PCM based on fatty acids, capric and palmitic acid, were nano-enhanced with low contents (1.0 wt.%, 1.5 wt.% and 3.0 wt.%) of copper (II) oxide (CuO) nanoparticles. Copper (II) oxide (CuO) was synthesized via coprecipitation method obtaining 60⁻120 nm diameter sized nanoparticles. Thermal stability and high thermal conductivity were observed for the nano-enhanced phase change materials (NEPCM) obtained. Experimental results revealed remarkable increments in NEPCM thermal conductivity, for instance palmitic acid thermal conductivity was increased up to 60% with the addition of 3 wt.% CuO nanoparticles. Moreover, CuO nanoparticles sedimentation velocity decreases when increasing its content.