Reactivity enhancement of chemical materials used in packed bed reactor of chemical heat pump

In this study, a mixture of expanded graphite (EG) and magnesium hydroxide (Mg(OH)(2)) was used to enhance the thermal conductivity and reactivity of a magnesium oxide/water (MgO/H(2)O) chemical heat pump, because EG is chemically stable and has high thermal conductivity and high moldability to form the heat exchange structure. Calcium chloride (CaCl(2)) was also introduced into the mixture of EG and Mg(OH)(2) to ensure smooth diffusion of vapor in materials and enhance the fittability between EG and Mg(OH)(2). The reaction kinetics of pure Mg(OH)(2), a mixed material containing Mg(OH)(2) and CaCl(2) (termed MC), and a mixed material containing EG, Mg(OH)(2), and CaCl(2) (termed EMC) were examined under the same reaction conditions by performing thermobalance measurements. EMC exhibited a higher dehydration rate than the other materials. It also exhibited hydration reactivity at temperatures of up to 200 degrees C; at this temperature, pure Mg(OH)(2) exhibited low reactivity. The addition of CaCl(2) also enhanced the hydration reactivity of MgO because of the high water adsorption ability of CaCl(2) in EMC. A reaction rate equation for the hydration of EMC was proposed on the basis of an assumed reaction model. The thermal performance of a MgO/H(2)O chemical heat pump manufactured using EMC was evaluated from this equation. EMC was concluded to have good potential for use as a packed bed material in the MgO/water chemical heat pump owing to its low cost, high hydration reactivity, high thermal conductivity, and high moldability to form the heat exchange structure. (C) 2011 Elsevier Ltd. All rights reserved.