Numerical study on the heat and mass transfer in charging and discharging processes of a triangular honeycomb thermochemical energy storage reactor

Adsorption heat storage based on porous adsorbents attracts considerable attention for the high energy storage density and long storage duration compared to sensible and latent heat storage methods. However, one of the critical challenges is the poor heat and mass transfer performance of thermochemical reactors. This study presents a triangular honeycomb reactor using zeolite 13X-H₂O working pair and investigates the heat and mass transfer performance. To do this, a three-dimensional transient heat and mass transfer model has been built in COMSOL to simulate the adsorption and desorption processes of the new reactor. A detailed numerical model and the corresponding modelling methods are critical to the investigation while most of the recent studies are based on one-dimensional and two-dimensional models. The model has been experimentally validated thoroughly to a close agreement in both adsorption and desorption processes (mean sum of percent errors of 0.6% to 8.91% for air temperature and relative humidity). The reactor thermal efficiency from the simulation and experiment are 19.57% and 21.93%, respectively, which are achieved by the fast and controllable charging and discharging performance along with the reduced air pressure drop benefited from the reactor design. To add value of the charging and discharging details, this study also presents the contour diagrams with detail discussions for the air velocity, temperature, water concentration, and heat and mass flux variations of the triangular honeycomb channel during desorption and adsorption processes. The results show that the side of triangle channel has larger and stronger moisture desorption in a charging process and stronger moisture adsorption in a discharging process than that of the triangle corner areas.