Numerical recipes for successfully modeling the phase transitions in thermal energy storage adsorption systems

Abstract

Strong convergence problems may arise during the dynamic simulation of the phase transitions of adsorption systems subjected to larger and/or random fluctuations of the boundary conditions, which do not follow the conventional cycle sequence (e.g., adsorptive thermal storage systems). This sequence could even be reversed at some instants and its stages not completed. Such convergence problems preclude solving those phase transitions, and thus the successful dynamic simulation of the adsorption systems. A set of numerical procedures for solving those problems is proposed, consisting of a small group of new conditions to be added to the conventional numerical algorithms. Its successful use is demonstrated in the dynamic simulation of a thermal energy storage system provided with an adsorption module, modeled in two distinct but coupled platforms (TRNSYS and MATLAB), for which the convergence difficulties are identified and described. Results indicate successful convergence by applying the proposed methodology, in contrast with the original algorithm, attesting for its capability to overcome the convergence problems that occur during the system's dynamic simulation. This set of numerical recipes can be adapted for other systems' algorithms, or to serve as a basis for its successful dynamic simulation, thus showing a promising and enlarged range of use.