Thermoanalytical Evaluation of Eutectic Mixtures of LiOH, NaOH and KOH for Latent Heat Thermal Energy Storage

Eutectic mixtures of Li0H, NaOH and KOH were selected as promising materials for latent iheat thermal energy strage devices because of their large heat of fusion and of low ma terial cost as described in a previous report (ref.10), and the eutectic points of LiOH-NaOH (30-70mol%), Li0H-KOH (29-71mol%) and NaOH-KOH (50-50mol%) were reported to be in an appropriate temperature range for thermal energy storage. Experimental eveluations of thermal properties of th e eutectic mixtures were carried out by thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC), because heats of fusion have not been reported and thermal behaviors, such as supercooling, , have large effects on the performances of the thermal enegy storage equipments. The eutectic mixtures were dried and melted in an electric vacuum oven, and the thermal analyses were made by using a poly(tetrafluoroethylene)-coated aluminum sample container 'under the flow of nitrogen. The hydroxides, especially KOH, are highly hygroscop ic, and the residual water has effects on their thermal properties, such as transition points and heats f transition (Fig.1). Every eutectic mixture shows little supercooling (Fig.4-6), and the eutectic points and heats of fusion for Li0H-NaOH LiOH-KOH and NaOH-KOH were 213.5°C, 330.J/g; 222°C, 184J/g and 165°C, 172J/g, respectively. If any devices are to be developed to overcome their cirawba, cks of hygroscopic and corrosive properties, these eutectic mixtures are very promi sing mat4rials for latent heat thermal enegy storage devices.