Abstract
To promote the development of thermal energy storage (TES), the sodium acetate trihydrate (SAT) presents interesting thermal properties. However, this material may suffer from aging throughout thermal cycles. Various solutions were explored in the literature to limit this aging, mainly based on the use of additives such as water. In this study, two samples were prepared. The first one consisted of raw SAT material whereas 3 wt.% of supplementary water has been added to the second one. They were then poured into 350 cm3 bricks, which were placed in an experimental test bench. After 35 cycles between 20 and 70 °C, a drop of about 10% of the latent heat was observed for the first sample. This behavior was like the literature data. For the second sample, the decrease of latent heat was more rapid (about 30%). Contrary to our expectations, the water addition seems not beneficial for the improvement of thermal stability. Interestingly, we noticed that the drop of the latent heat was fully reversible after sample stirring. This degradation might not be related to a thermal destructive mechanism but rather to a global segregation phenomenon. This segregation may be due to the breaking of hydrogen bonding between anhydrous sodium acetate and water, resulting in the separation of the two species.
Highlights
Phase change materials (PCMs) appear as an attractive solution for thermal energy storage and for the development of renewable energies
Many thermal cycles may be applied to the material that may suffer from aging, resulting in a decrease of the latent heat
One of the most interesting materials issued from this class of PCMs is sodium acetate trihydrate (SAT, CH3COONa·3H2O)
Summary
Phase change materials (PCMs) appear as an attractive solution for thermal energy storage and for the development of renewable energies. The separation of species will increase with cycles, as the mobility is limited both in liquid (no agitation) and in solid state as the remaining SAT in the middle-height will crystallize and hinder the contact between the two species This would decrease the latent heat released by the material, leading to a reduction of its storage capacity. Dannemand et al [14,15] have shown that a sample of SAT with 48.7 wt.% of water (9 wt.% of extra water) can suffer from aging during thermal cycling It was observed a decrease of 8% of its latent heat, from 194 to 179 kJ/kg−1 after 14 cycles. As solidification could be triggered, it was possible to compare the degradation of the latent heat in both samples
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