Model experiment and numerical study on the heat storage law of phase change material in different heat transfer structures

Abstract

Phase change thermal storage is currently the hottest research topic in the energy field. This article adopts the rectangular box, which can be changed with 3 kinds of piping structures (bare copper tube, bare copper tube plus sparse, and plus dense aluminum fins). The heat storage process of paraffin wax (PW) and PW + 4 % expanded graphite (EG) was analyzed by experimental tests and numerical simulations. It was verified that the PW heat storage process occurs through thermal conductivity and natural convection, and the addition of fins weakens natural convection. The thermal conductivities of PW with 4 %, 8 %, and 12 % EG were determined to be 5.31, 12.10, and 18.06 times higher than that of PW, respectively. Research finds bare copper tubes plus aluminum fins enhance the heat storage rate of PW significantly more than PW + EG composites; the impact of excessive aluminum fin additions was insignificant. The heat storage process of PW + 8 % EG and PW + 12 % EG was further investigated by numerical simulation. Deep investigation indicates that an increase in the EG fraction enhances thermal storage power but reduces thermal storage capacity. In all the cases studied, PW + 8 % EG composite with bare copper tube and sparse aluminum fin structure compared with PW material with bare copper tube structure, the thermal storage capacity is only reduced by 18.35 %, but the thermal storage power is increased by 473.9 %. This design case has the choice advantage and provides a valuable reference for practical application.