Heat transfer analysis of hollow channel in phase change materials spherical capsule

Abstract

• A PCM spherical capsule with simple and low-cost hollow channel is presented. • The conduction and natural convection in the center of capsule are enhanced. • The effect of angle and diameter are investigated experimentally and numerically. • The heat storage time reduced by 28% with a dimensionless diameter of 0.25. The packed bed thermal energy storage device (PBTESD) filled with spherical phase change capsules can overcome the mismatch between the energy supply and the heat demand, which has broad application prospects. In this paper, a spherical phase change material capsule with a hollow channel with a simple, low-cost heat transfer enhanced structure has been proposed and studied. Experiments were carried out to measure the temperature of the typical capsule and capsule with hollow channel during the melting process to study the feasibility of the structure. Moreover, a three-dimensional numerical model based on the enthalpy method is established and verified by experiments. In order to optimize the structure and study the effect of random placement on the performance of hollow channels, the effects of the angle and diameter of the hollow channel on the thermal performance are analyzed by numerical simulation. A 24% increase in melting rate is found through experimental temperature profiles preliminarily. Besides, it is found that the performance decreased by 26.7% when the angle of the hollow channel decreasedfrom 30° to 0°, and the performance is similar when the angle is between 30° and 90°. In addition, the energy storage time decreases linearly with the increase of the diameter when the dimensionless diameter d/D is bigger than 0.05. Increasing the dimensionless diameter can improve the performance of the hollow channel, but it also reduces the phase change material filling rate. The melting time is shortened by about 28% when d/D=0.25. This paper indicated the transient thermal properties of the spherical capsule with hollow channel during constraint melting, which laid a foundation for further structural optimization and practical application.