Porosity and density measurements of sodium acetate trihydrate for thermal energy storage

Abstract

Sodium acetate trihydrate (SAT) can be used as phase change material in latent heat storage with or without utilizing supercooling. The change of density between liquid to solid state leads to formation of cavities inside the bulk SAT during solidification. Samples of SAT which had solidified from supercooled state at ambient temperature and samples which had solidified with a minimal degree supercooled were investigated. The temperature dependent densities of liquid and the two types of solid SAT were measured with a density meter and a thermomechanical analyzer. The cavities formed inside samples of solid SAT, which had solidified after a high or minimal degree of supercooling, were investigated by X-ray scanning and computer tomography. The apparent density of solid SAT depended on whether it solidified from a supercooled state or not. A sample which solidified from a supercooled liquid contained 15% cavities and had a density of 1.26 g/cm 3 at 25 °C. SAT which had solidified with minimal supercooling contained 9% cavities and had a density of 1.34 g/cm 3 at 25 °C. The apparent densities of the solid SAT samples were significant lower than the value of solid SAT reported in literature of 1.45 g/cm 3. The density of liquid and supercooled SAT with extra water was also determined at different temperatures.

Demonstration of a solar combi-system utilizing stable supercooling of sodium acetate trihydrate for heat storage

“…Its melting point of 58 °C, the low price for industrial use (typically below 0.5 Euros per kilogram in large quantities) and its non-toxic properties are appropriate for heat supply in buildings. Its density has been determined to be 1.27 kg/L at 90 °C in liquid state and 1.33 to 1.34 kg/L in an open sample after solidification from supercooled state [35].…”

“…The density (ρ) of SAT in liquid phase is lower than in solid phase and must be therefore used. A minimum density of 1.27 kg/L at 90 °C [35] was considered. In discharge tests, a minimum SAT temperature of 50 °C was found to be necessary for heat supply.…”

Sustainable enhancement of district heating and cooling configurations by combining thermal energy storage and life cycle assessment

“…Regarding LTES2, the issue of phase separation was taken into account, and therefore, SAT with carboxymethyl cellulose (CMC) as a thickening agent was considered (mass fraction 1%) (Kong et al 2019). SAT has a melting point of 58 ºC, relatively high melting enthalpy at 264 kJ/kg (Dannemand et al 2015), and within its operation temperature, density is between 1.25 kg/m 3 and 1.45 kg/m 3 (Dannemand et al 2018). Also, SAT presents stable supercooling, and therefore, generally reliable mechanisms are required for the controlled initialization of crystallization (Englmair et al 2018a).…”

Crystallization by local cooling of supercooled sodium acetate trihydrate composites for long-term heat storage

“…It has been identified as a potential heat storage material due to its relatively high heat of fusion (264 kJ kg −1 [2]; 237-243 kJ kg −1 [3]; ) and its relatively high specific heat capacities in both liquid and solid phases [4]. The density of solid SAT in a closed sample that has solidified from supercooled state has been determined to be 1.24-1.28 kg L −1 [5]. SAT is attractive for domestic heat storage applications because of its high volumetric heat storage capacity (~500 kJ L −1 from 20 °C in solid state to 80 °C in liquid state), the low price and its non-toxic properties.…”