On the optimal heat source location of partially heated energy storage process using the newly developed simplified enthalpy based lattice Boltzmann method

The present study aims to fill the knowledge gap in the partially heated energy storage process by finding the optimal heat source location. A new simplified enthalpy based lattice Boltzmann method is proposed for the present work. The new model follows the predictor-corrector step, while the traditional model follows the collision-streaming step. Compared to the traditional model, this new model has the same accuracy, but it has advantages on virtual memory saving and physical boundary treatment due to its unique structure. Besides, in the partially heated energy storage process, the heat source location can pose significant impact on the charging efficiency and the energy storage rate. The optimal heat source location is where the maximum charging efficiency and energy storage rate are achieved. Results indicate that, a small region with the length of 0.1 l can be deemed as the optimal region for the heat source location, for that the charging time and the energy storage rate at various locations inside that region are almost the same. The optimal region decreases with the increase of Rayleigh and Prandtl numbers. In addition, the optimal regions for some specific heat source lengths and Rayleigh numbers are obtained. Based on these results, a map is provided to indicate the variations of the optimal region. According to this map, the optimal heat source locations for more varied conditions can be estimated through the heat source length and the Rayleigh number, which would be quite useful and significant for the thermal design in various engineering applications.