A mathematical model of charging and discharging processes in a thermochemical energy storage reactor using the hydrated potassium carbonate as a thermochemical material
Natalia Mikos-Nuszkiewicz, Piotr Furmański, Piotr Łapka
Abstract
The paper presents a new mathematical model of the processes of charging and discharging a thermochemical energy storage (TChES) reactor with a high potential for effective application in a residential building. The model is an intermediate approach between lumped-element models and 2D/3D spatially resolved models. The paper also contains the results of the numerical implementation of the developed model. The efficiency of the storage process is one of the key parameters describing the operation of the system, and the study of the impact of individual factors on its value is one of the main goals of the work carried out. A system for heat accumulation using solar collectors and a fixed bed thermochemical reactor was proposed for the analysis. The K2CO3 hydration/dehydration reaction was selected for analysis purposes, but the model is also valid for other reversible reactions. The following parameters describe the considered reactor operations: specific humidity and temperature of the moist air in the reactor, degree of transformation of K2CO3·1.5H2O into K2CO3 and bed temperature across the reactor. Their temporal and spatial variations in the reactor enable finding the amount of energy accumulated in the reactor during the charging process (or the amount of heat rejected to the moist air in the reactor during the discharging process). Therefore, the efficiency of the storage process (or the efficiency of the discharging process) can be determined. The simulation results provide insight into the multi-physical phenomena occurring during heat accumulation and release processes. Therefore, they help identify the factors with the most significant impact on the proposed reactor's operation. It was found that the species conversion process and amount of heat stored are affected by the bed geometry (ratio of the inner and outer radius of the reactor, bed and particles porosity, and diameter of the bed particles) as well as reactor's diffusive properties. The developed model and presented results might facilitate the creation of valuable experimental setups and save the time and resources spent on unsuccessful experimental attempts.