Proof of concept for unsteady dynamic model of sorption thermal battery with H2O/LiBr and universal methodology to optimize energy storage density

This study presents an unsteady dynamic model developed specifically to address limitations in conventional modeling of sorption thermal battery. The model introduces the concept of effective specific heat capacity to represent sensible and latent heat transfer under a single framework, and explicitly considers the transient evolution of vapor mass, pressure, and energy by treating the vapor domain as thermodynamically active unlike conventional quasi-steady models, which assume instantaneous vapor-liquid equilibrium and negligible vapor dynamics. Sorption thermal battery poses unique modeling challenges due to sharp transitions between subcooled and saturated solution regions. The presented model establishes a vapor-liquid equilibrium time scale as a function of chamber volume and hot water velocity, providing a boundary for the applicability of quasi-steady models. Experimental validation using a 1 kW prototype shows strong agreement with simulation results, achieving an energy storage density of 188 kWh/m3. This work not only resolves critical gaps in transient modeling but also proposes a universal methodology for optimizing energy storage density based on dimensionless time constants and vapor-liquid equilibrium dynamics. This provides a foundation for the accurate design and control of sorption thermal battery.