Optimization of sorption thermal battery via breakthrough curve modeling and experimental validation

This study provides guidelines for the optimal design and operating conditions of the sorption thermal battery (STB) reactor. While significant progress has been made in material-level optimization through the development of novel composite adsorbents, research on system-scale optimization remains limited. Consequently, understanding the effects of operating conditions on STB performance still largely relies on case-by-case experimental approaches, hindering the practical application of STB. To address this, a breakthrough curve model is used to predict STB performance—specifically, energy storage density (ESD) and operating time—under varying conditions and to identify optimal conditions. The model is validated through proof-of-concept STB reactor experiments. Comprehensive material characterization is also performed to identify the optimal working pair, enabling optimization from the material level to the reactor scale. The results confirm that 15 wt% LiOH-impregnated zeolite 13X is the optimal adsorbent, achieving an ESD of 2175 kJ kg_ads⁻¹, surpassing other LiOH-based composite adsorbents reported in the literature. Operating conditions including vapor concentration, flow rate, and reactor length are integrated using the nondimensional adsorption distance coordinate ξ, enabling a generalized analysis of operating conditions. The optimal operating range is determined to be ξ = 0.105-0.118, achieving a maximum system-level ESD of 188.4 kWh m⁻³— representing a 38 % improvement compared to 136.3 kWh m⁻³ at ξ = 0.038. Furthermore, experimental validation confirms that reactors operating at identical ξ values exhibit consistent breakthrough profiles and ESD, regardless of individual input parameters. These results have the potential to guide the optimal design of STB for low-grade heat utilization.