Modeling of heat transfer and fluid flow in epsom salt (MgSO_4•H_2O) dissociation for thermochemical energy storage

摘要

For describing the thermochemical energy storage in salt hydrates, a model for dissociation of a salt hydrate is presented in this work. The model comprehensively integrates the attendant transport phenomena of the dissociation process, reaction kinetics and convection of the generated vapor. Local salt hydrate particle size and permeability variation in the system resulting from the dissociation reaction, heat transfer and flow of vapor in the evolving porous medium are accounted. The coupled governing equations of chemical reaction rate, mass, momentum and energy are solved by a finite volume-based numerical method. The model is validated with the benchmark numerical result available in literature. Using the model the thermochemical dissociation of epsom salt in a thermal storage system is simulated. The transient evolution of temperature, concentration and flow fields during the dissociation reaction is described. System's performance is quantified with the help of performance indicators such as sensible, chemical, total energy and effectiveness. For the first time, the role of vapor flow on the physical behavior of the thermochemical energy storage system is delineated. It is observed that the flow of water vapor significantly influences system's temperature distribution which in turn influences all other physical aspects, such as local and global heat transfer, reaction progression, concentration field and storage performance of the system.