Heat Release Behavior during Hydration Reaction of β-Lanthanum Sulfate/Thermally Expanded Graphite Composite for Use as Chemical Heat Storage Material

Abstract

The present work investigates the hydration reaction of a composite made up of β-lanthanum sulfate and thermally expanded graphite for possible use as a chemical heat storage technique for exhaust heat below 250°C. The e ects that water concentration and hydration temperature exert on hydration behavior were mainly studied via the use of a disklike pelletized sample with a β-lanthanum sulfate content of 98 wt%. These e ects were experimentally investigated using a thermal-gravimetric apparatus. The maximum hydration rate increased as the water vapor concentration increased under a hydration temperature of 110°C. Moreover, the maximum heat power density was 2.1 MW/m 3 at a water vapor concentration of 17.5 mol/m 3 . Furthermore, the near-nal values of the hydration numbers that were found at 30 min decreased as the hydration temperature increased to a range of from 110 to 180°C. In the initial stage, however, hydration rates were not dependent on temperature under the present experimental conditions. The temperatures inside the pelletized samples during hydration were also measured. These temperatures drastically increased immediately after the start of hydration regardless of the beginning temperature. For instance, a maximum value of 195°C was obtained at a hydration temperature of 130°C with a water concentration of approximately 17.1 mol/m 3 .