Cycling Stability of Calcium-Impregnated Vermiculite in Open Reactor Used as a Thermochemical Storage Material

Abstract

Recent research into thermochemical storage (TCS) materials has highlighted their promising potential for seasonal building heating, through energy capture and release during dehydration and hydration cycling. A common TCS material used throughout this investigation was calcium chloride (CaCl2)-impregnated vermiculite-based salt in matrix (SIM). This material was assessed for its robustness during charging and discharging cycles to assess its behavior and in terms of energy stability and chemical stability; the results of which showed consistent volumetric energy density and maximum temperature changes over seven cycles. The calcium SIM did, however, show a decline in leachable Ca content, which was presumed to be a result of stabilization within the vermiculite, and chloride concentration showed little change over the course of the study. Real-time visualization using a high-resolution microscope of calcium SIM particles showed a salt phase change and migration of liquid salt into the valleys of the lamella. A novel cobalt chloride (CoCl2) SIM was used to visualize the hydration path across the particle, through distinct color changes depending on hydration state. The results indicated that the topography of the vermiculite played a significant role in the passive hydration modeling.

Keywords

• thermochemical storage
• calcium chloride
• vermiculite
• stability
• charge and discharge cycling