Numerical Analysis of a Small-Scale, Low-Temperature Sorption Storage Unit Using a Novel Non-Equilibrium Multiphysics CFD Model

This study presents a novel multiphysics numerical model for sorption-based thermal energy storage (TES) systems incorporating local thermal and hygric non-equilibrium in the reaction bed. The model fully accounts for coupled heat, mass, and momentum transfer along with sorption/desorption kinetics within a porous reaction bed. The model was tested and used to perform a parametric analysis of a small-scale silica gel-air system to evaluate the effects of various operating parameters of the unit and parameters of the reaction bed. The analysis revealed that the diameter of the silica gel granules had the greatest impact on the maximum charging effectiveness, for example, for 7 mm granules it was 12.5%, while for 1 mm granules it increased to 19.4% due to improved mass transfer and surface area. The discharging outlet temperature was more strongly affected by the inlet air temperature and relative humidity than by the air inlet velocity. At higher inlet temperatures, the increase in outlet temperature during the discharging process was greater, for example, at 15°C, the air was heated to 27.6°C, whereas at 20°C, it was heated to 36.2°C. In turn, the inlet velocity greatly affected the sorption reaction power. During discharging, the maximum power was 20 W at an inlet velocity of 1 m/s and increased to 66.6 W at 4 m/s. During charging, the maximum power was 44.7 W at 1 m/s and increased to 150.7 W at 4 m/s. Moreover, the model provides insights into transport limitations and enables design optimization of sorption TES systems.