Thermal performance analysis and optimization of a spherical PCM capsule with pin-fins for cold storage

Abstract

A spherical phase change material (PCM) capsule with circular pin-fins for latent cold thermal energy storage is proposed and studied in this paper. Experiments were conducted to monitor the PCM temperature variation in each capsule during solidification in order to validate the simulated results calculated based on the enthalpy method. Good agreement was found between the simulated values and experimental data and the deviations were lesser than 6.9%. Thermal performances, including the temperature variation, liquid fraction distribution as well as cold charging rate, of the capsules with various pin-fin configurations were numerically compared. Results demonstrate that the cold charging rate is improved dramatically due to the insertion of fins, and the cold charging time is decreased by more than 50% in the capsule with six fins (approximately 3600 s) compared to that without fins (approximately 7700 s). In addition, the increasing extent is positively related to the pin-fin number, despite the slight reduction of PCM filling ratio. Furthermore, it is indicated that the thermal performance can also be improved by means of optimizing geometric parameters of pin-fins, such as their length L and diameter D. As for the spherical capsule with an inner radius of R = 20 mm, the optimal parameter is regarded to be L/R = 75% and D = 2 mm.