Heat transfer and storage characteristics of a hexagonal close structured packed-bed thermal storage system with molten salt phase change materials

The phase change material (PCM) spheres using 316SS as the ball shell and solar salt (NaNO3-KNO3, 60-40 wt%) as the PCM were arranged in an orderly pebble-bed arrangement. The charging performance, energy and exergy of PCM spheres in the packed ball thermal energy storage system (PBTES) were investigated using CFD simu-lation in order to solve the problem of heat storage at 300 degrees C-500 degrees C. The results show that the total melting time of PCM spheres slightly decreases from 1455 s to 1319 s with the inlet velocity increasing. The average heat storage efficiency of PCM spheres and PBTES are improved with the inlet temperature increasing. When the inlet flow rate increases from 0.01 m/s to 0.10 m/s, the energy efficiency of PBTES increases approximately 5.06 times, and the exergy efficiency increases from 17.91 % to 99.55 %. However the heat energy storage and exergy efficiency of PCM spheres are not affected by the inlet velocity changing. The energy efficiency of PBTES in-creases about 2.09 times, and the exergy efficiency increases from 30.29 % to 70.93 % with the inlet temperature grows from 300 degrees C to 500 degrees C. It provides an idea for the design of the medium-high temperature and high-efficiency molten salt PCM heat storage system.