Enhancement of heat and mass transfer of potassium carbonate-based thermochemical materials for thermal energy storage

Abstract

Salt hydrates are ideal for long-term thermochemical heat storage in a built environment, where K2CO3 is considered a promising thermochemical heat storage material. This class of materials continues to encounter certain technical bottlenecks in practical applications, and the enhancement of heat and mass transfer is a key challenge. Composite materials are a promising method to address this challenge because heat and mass transfer are coupled and material-dependent. In this study, a novel K2CO3-based composite material was synthesized from expanded graphite (EG), K2CO3, and octylphenol polyoxyethylene(10) ether (OP-10), and its structural information, reaction kinetic properties, thermodynamic properties, and cycling stability were determined. The results showed that the use of EG with OP-10 significantly enhanced mass and heat transfer. Compared to pure K2CO3, the thermal conductivities of the composites were increased by 9–15 times and their half-conversion time was shortened by approximately 3/4–4/5, indicating that their mass and heat transfer capacities were effectively improved. The mass and volume energy storage densities (ESDs) of K2CO3-based composites reached 429–563 kJ⋅kg−1 and 138–216 kWh⋅m−3, respectively, and these values depended on the content of K2CO3. In addition, the cycling stability results indicated that these K2CO3-based composites performed well and were suitable for medium-to-low-temperature thermochemical thermal storage applications.