Numerical Investigation of Effect of Fin Geometry on Melting Process of Phase Change Material in an Evacuated Tube Solar Collector

This paper investigates the melting behavior of phase-change material (PCM) in an evacuated tube solar collector. The outer tube was made of borosilicate glass with a diameter of ۶۰ mm, and the inner tube was made of copper with a diameter of ۱۰ mm and length of ۱۵۰۰ mm. The heat transfer problem in heat pipe was investigated in four cases: finless, full fin, half fin, and third fin. The fins were cut from a ۳۵ mm diameter copper tube and installed concentrically with the outer tube. The inner space between the absorber tube and the heat pipe was filled with stearic acid as the PCM. The numerical simulation was conducted using the Ansys Fluent ۲۰۲۲ for the laminar incompressible Newtonian fluid flow in the transient state via the enthalpy-porosity model. The initial temperature of PCM was ۲۷°C, and liquid fraction was zero at the beginning of the simulation. After validating the numerical results with experimental ones, the collector performance was evaluated by considering the four temperatures of ۶۸, ۷۲, ۷۶, and ۸۰°C for the fin and heat pipe at three different times t = ۲۲, ۵۵, and ۱۱۰ s. The results showed that by increasing the fin area in three cases of third fin, half fin, and full fin, the melting and storage time of PCM were reduced by ۶%, ۴۴%, and ۸۷%, respectively. Also, as the Estefan number increased from ۰.۰۰۷ to ۰.۰۵, ۰.۰۹, and ۰.۱۳, the process of PCM melting decreased by ۷۵%, ۸۵%, and ۹۲%, respectively.

Keywords:

PCM , Fin , Thermal Conduction , Natural Convection , Enthalpy-Porosity