Melting and solidification processes of phase change material in evacuated tube solar collector with U-shaped spirally corrugated tube

Abstract

Most important challenge in evacuated tube solar collector is lower performance in off-pick hours of sunlight which leads to utilizing thermal energy storage. In present study, thermal performance of evacuated tube solar collectors (because of its enormous application range) integrated with phase change material is evaluated, numerically. The corrugated tube is used instead of smooth tube. The proposed system which is an evacuated tube solar collector equipped with corrugated U-shaped tube and phase change material to store the additional thermal energy in pick hours of sunlight, is the innovation of present work. Numerical simulations were performed for both melting and solidification processes of phase change material. The influences of number of lobe, pitch and depth corrugated on thermal processes of proposed collector are analyzed. The results showed that although the collector outlet temperature in some cases were slight different, however, a significant enhancement in daily thermal efficiency is observed due to the longtime discharging process at night. The corrugated tube increases the collector efficiency by 21.55% compared to smooth tube. Furthermore, four-lobe corrugated tube retains the collector’s operation temperature up to 40 °C. Also, between investigated geometrical parameters, number of lobe has most impact on thermal performance.