Numerical analysis of the effects of using different heat and moisture carrier gases in a sorption thermal energy storage unit

Among the various thermal energy storage (TES) methods, sorption/thermochemical energy storage (TChES) remains the least mature. Several laboratory-scale TES prototypes utilizing this technology, developed through numerical modeling, have been reported in the literature. Accordingly, further advancements in this technology require the development of more sophisticated models. Reliable numerical models can contribute to the development of more efficient TChES units that can be integrated into modern energy systems. This paper presents an innovative numerical model that brings a new quality to the modeling of sorption TES. The key element of the proposed model is that it rigorously treats the fundamental physical processes occurring within the TES system. In particular, it takes into account the local thermal and hygric non-equilibria in the reaction bed. The proposed model was tested and applied to analyze the effects of using different heat and moisture carrier gases in a small-scale sorption TES unit. The carrier gases studied included air, carbon dioxide, argon, and nitrogen. The analysis evaluated the influence of these gases on both the charging and discharging processes. Three methods of feeding the TES were investigated: constant fluid volumetric flow rate, constant mass flow rate, and constant enthalpy supply. The results show that argon was the most effective carrier gas for the charging process, achieving an instantaneous effectiveness of over 20% in all cases. Additionally, argon had the highest heating potential during the discharging process, with the outlet temperature from the unit peaking above 40°C. In comparison, the instantaneous effectivenesses and outlet temperatures for air/nitrogen and carbon dioxide were significantly lower.