Charging and discharging performances investigation for a vertical triplex-tube heat exchanger with a tapered configuration and reverse layout

Given the inherent low thermal conductivity of phase change materials, the majority of previous research has focused on heat transfer intensification for the double-tube heat exchanger. However, a triplex-tube heat exchanger (TTHX) delivers a larger heat transfer area. To further elevate the heat transfer properties, a TTHX with a tapered configuration is proposed. How the tapered structure boosts heat transfer and the impact of cone angles on the charging and discharging performances of TTHX are investigated. Results demonstrate that employing the tapered structure significantly elevates the charging rate, and the charging time exhibits a trend of first declining and subsequently rising as θ increases from 3° to 8°, where the optimal cone angle (θ = 6°) shortens the charging time by 40.41% compared to θ = 0°. However, the heat transfer during solidifying is inhibited, and the inhibition becomes more pronounced as θ increases. This negative effect can be remarkably improved by imposing a reverse layout, which reduces the discharging time by a maximum of 32.54% compared to devices without reverse layout. This study offers a new perspective for the optimization research of the charging and discharging performances of TTHX and can provide guidelines for the optimization design of TTHX.