Thermal Storage in Ammonium Alum/Ammonium Nitrate Eutectic for Solar Space Heating Applications

Ammonium alum and ammonium nitrate in the weight ratio of 1:1 form a eutectic that melts at 53°C and solidifies at 48°C. The thermophysical properties of this eutectic were measured in detail and the eutectic was found to have properties desirable for energy storage for solar space heating applications. The eutectic was encapsulated in 0.0254-m diameter high-density polyethylene (HDPE) balls and packed into a cylindrical bed in a scale model for testing its heat transfer characteristics when exposed to an air flow. Test results indicate that the thermal extraction efficiency of the model was 89 percent with an uncertainty of ±8.0 percent. The packed bed had a Stanton number value in close agreement with that predicted with an empirical equation for sensible heat extraction from the eutectic in the solid phase. This Stanton number was increased by about 74 percent for sensible heat extraction from the eutectic in the liquid phase, a phenomenon not previously reported in the literature.