Numerical analyses and optimization of tubular thermochemical heat storage reactors using axisymmetric thermal lattice Boltzmann model

Abstract

Axisymmetric lattice Boltzmann (LB) model has gained great development in the field of fluid flow and heat transfer in recent decades. Compared with the standard LB method, the axisymmetric LB method can solve 3D axisymmetric problems with minimal meshes. This numerical method will be helpful in research on thermochemical heat storage, especially considering the profound understanding and optimization of reactor performance. In this study, we extended a previous axisymmetric LB model to simulate the charging/discharging processes of a MgO/Mg(OH)2 thermochemical reactor. We derived a new evolution function by including an unstable heat source term out of a chemical reaction. New isothermal and heat flux boundary treatment approaches were proposed to maintain the precision of this axisymmetric LB model in the presence of the heat source term. In addition, a local method for transient conjugate heat transfer simulation without the utilization of temperature gradient information at the fluid-solid interface was developed to predict heat transfer between the reactor bed and heat transfer fluid. With the proposed axisymmetric thermal LB model, the charging/discharging processes of a tubular MgO/Mg(OH)2 thermochemical reactor unit with a heat exchanger were simulated. Results showed that the average power output was maximized with a bed thickness of 1.0 cm. The length of the reactor unit should be considered by balancing power output and cost.